Protective diode (suppressor): operating principle, how to test a TVS diode. How to check a diode with a multimeter

Testing an LED with a multimeter is the easiest and most correct way to determine its performance. A digital multimeter (tester) is a multifunctional measuring instrument, the capabilities of which are reflected in the switch positions on the front panel. LEDs are checked for functionality using functions present in any tester. Let's look at the testing methods using the DT9208A digital multimeter as an example. But first, let’s touch a little on the topic of the reasons for the malfunction of new light-emitting diodes and the failure of old ones.

The main causes of malfunction and failure of LEDs

A feature of any emitting diode is its low reverse voltage limit, which is only a few volts higher than the drop across it in the on-state. Any electrostatic discharge or incorrect connection during circuit adjustment can cause the LED (abbreviation for Light-emitting diode) to fail. Ultra-bright, low-current LEDs, used as power indicators for various devices, often burn out as a result of power surges. Their planar counterparts (SMD LEDs) are widely used in 12V and 220V lamps, strips and flashlights. You can also verify their serviceability using a tester.

It is worth noting that a small proportion of defective LEDs (about 2%) are supplied from the manufacturer. Therefore, additional checking of the LED with a tester before mounting it on a printed circuit board will not hurt.

Diagnostic methods

The simplest method, which is most often used by radio amateurs, is to check light-emitting diodes with a multimeter for performance using probes. The method is convenient for all types of light-emitting diodes, regardless of their design and number of pins. Having set the switch to the “continuity check, open circuit” position, touch the leads with the probes and observe the readings. By connecting the red probe to the anode and the black probe to the cathode, the working LED should light up. When changing the polarity of the probes, the number 1 should remain on the tester screen.

The glow of the emitting diode during testing will be small and on some LEDs in bright light it may not be noticeable.

To accurately test multi-color LEDs with multiple leads, you need to know their pinout. Otherwise, you will have to randomly sort through the terminals in search of a common anode or cathode. Don't be afraid to test high-power LEDs with a metal substrate. The multimeter is not capable of disabling them by measuring in dial mode.

Testing an LED with a multimeter can be done without probes, using sockets for testing transistors. Typically, these are eight holes located at the bottom of the device: four on the left for PNP transistors and four on the right for NPN transistors. The PNP transistor is opened by applying a positive potential to the emitter “E”. Therefore, the anode must be inserted into the socket labeled “E”, and the cathode into the socket labeled “C”. A working LED should light up. To test in the holes for NPN transistors, you need to change the polarity: anode - “C”, cathode - “E”. This method is convenient for testing LEDs with long and solder-free contacts. It does not matter in what position the tester switch is located.
Checking an infrared LED occurs in the same way, but has its own nuances due to invisible radiation. At the moment the probes touch the terminals of the working IR LED (anode - plus, cathode - minus), a number of about 1000 units should appear on the device screen. When changing polarity, the screen should display one.

To check the IR diode in the transistor testing sockets, you will additionally have to use a digital camera (smartphone, telephone, etc.). The infrared diode is inserted into the corresponding holes of the multimeter and the camera is pointed at it from above. If it is in good condition, then IR radiation will be displayed on the gadget’s screen in the form of a glowing blurry spot.

Testing high-power SMD LEDs and LED matrices for functionality requires, in addition to a multimeter, a current driver. The multimeter is connected in series to the electrical circuit for several minutes and the change in current in the load is monitored. If the LED is of poor quality (or partially faulty), then the current will gradually increase, increasing the temperature of the crystal. The tester is then connected in parallel with the load and the forward voltage drop is measured. By comparing the measured and passport data from the current-voltage characteristics, we can conclude that the LED is suitable for use.

Diode check.

To make it more clear, let’s check the 1N5819 rectifier diode. This is a Schottky diode. We will soon see this.

We will check with a multitester Victor VC9805+. Also, for convenience, a solderless breadboard is used. Please note that during measurements you cannot hold the leads of the diode and multimeter probes with both hands. This is a big mistake. In this case, we measure not only the parameters of the diode, but also the resistance of our body. This can significantly affect the result of the test. You can only hold the probes and diode leads with one hand! In this case, only the measuring device itself and the diode being tested are included in the measuring circuit. This recommendation is also valid when measuring the resistance of resistors, as well as when checking capacitors. Don't forget this important rule.

So, let's check the diode in direct connection. In this case, the positive probe ( red) connect the multimeter to the anode of the diode. Negative probe ( black) connect to the cathode of the diode. In the photo shown earlier, you can see that the cylindrical body of the diode has a white ring on one edge. It is on this side that the diode has a cathode terminal. This is how the cathode terminal of most imported diodes is marked.

As you can see, the threshold voltage value of the 1N5819 diode appeared on the display of the digital multimeter. Since this is a Schottky diode, its value is small - only 207 millivolts (mV).

Now let's check the diode in reverse connection. We remind you that when switched in reverse, the diode does not allow current to pass through. Looking ahead, we note that even in reverse switching, the diode still passes current. This is the so-called reverse diode current ( I arr.). But it is so small that it is not taken into account.

Let's change the connection of the diode to the multimeter's test leads. Red connect the probe to the cathode, and black to the anode.

The display will show “ 1 " in the most significant digit of the display. This indicates that the diode does not pass current and its resistance is high. So we checked the 1N5819 diode and it turned out to be fine.

Diode faults.

The diode has two main faults. This breakdown p-n junction and break p-n junction.

Breakdown . During a breakdown, the diode turns into an ordinary conductor and freely passes current, either in the forward direction or in the reverse direction. In this case, as a rule, the multimeter buzzer beeps, and the display shows the diode resistance value. This resistance is very small and amounts to several ohms.

Break . When broken, the diode does not pass current either in forward or reverse connection. In any case, the device display shows “ 1 " With such a defect, the diode is an insulator. “Diagnosis” - a break can be accidentally caused to a working diode. This is especially easy to do when the tester probes are worn out and damaged. Make sure that the measuring probes are in good condition; their wires are oh-so-thin and easily break with frequent use.

And now a few words about how the value of the threshold voltage can be used to roughly judge the type of diode and the material from which it is made.

Here is a small selection made up of specific diodes and their corresponding threshold voltage values, which were obtained when testing these diodes with a multimeter. All diodes were previously checked for serviceability.

As we can see, the lowest threshold voltage ( V f) for Schottky diodes 1N5822 and 1N5819. This is a distinctive feature of Schottky diodes. When current flows through them in the forward direction, a very small voltage drops at their p-n junction. To put it simply, the diode offers virtually no resistance to the flowing current and does not waste precious watts. The opposite situation occurs with silicon diodes. Their forward voltage drop, as a rule, is no less than 0.5 volts, or even more. Silicon diodes and Schottky diodes are widely used for AC rectification. For example, as part of a diode bridge.

Germanium diodes have a forward voltage drop of 300 - 400 millivolts. For example, the D9 germanium point diode we tested, which was previously used as a detector in radio receivers, has a threshold voltage of about 400 millivolts.

Schottky diodes have a threshold voltage in the region of 100 – 250 mV;

For germanium diodes, the threshold voltage is usually 300 – 400 mV;

Silicon diodes have the highest threshold voltage of 400 – 1000 mV.

Thus, using the described technique, you can not only determine the serviceability of the diode, but also approximately find out what material and what technology it is made of. This can be determined by the threshold voltage.

A simple way to test an LED without desoldering it from the circuit. Checking the diode with a multimeter on the board

how to check a diode with a multimeter (ring with a tester)

Like most measuring instruments, multimeters (testers) are divided into analog and digital. Their main difference is that information about the measurement results of the first type is transmitted using a certain scale and arrows on it, while in the second case this data is displayed digitally on a liquid crystal screen.

Analog devices appeared earlier; their main advantage is their low price, and their disadvantage is measurement inaccuracy. Therefore, if the mark needs to be as accurate as possible, it is recommended to purchase a digital multimeter.

All tester options have at least two outputs - red and black.

The first is used directly for measurements, also sometimes called potential,
The second one is general. Modern models usually also have a switch, thanks to which it is possible to set the maximum limit values.

How to check a diode with a multimeter?

A diode is an element that conducts electricity in one direction. If you reverse this direction, the diode will be closed. Only if this condition is met, the element is considered operational. Most tester models already have such a function as checking a diode with a tester.

Before starting the test, it is recommended to connect two multimeter probes together to make sure it is working, and then select the “diode test mode”. If the tester is analog, this operation is performed using the ohmmeter mode.

Checking diodes with a multimeter does not require additional skills. To ensure that the element is functioning, it is necessary to perform a direct connection, therefore, connect the anode to the positive value (red probe) and the cathode to the negative value (black). The value of the diode breakdown voltage should appear on the screen or scale of the device; this figure averages from 100 to 800 mV. If you turn it back on (swap the electrodes), the value will not be more than one. From this we can conclude that the resistance of the device is enormous and it does not conduct electricity. If everything happens exactly as described above, the electronic element is operational and functional.

There are situations when, when connecting probes, the diode passes current in both directions, or does not pass it at all (the values for direct and reverse connections are equal to one). In the first case, this means that the diode is broken, and in the second, it is burned out or has an open circuit. Such electronic elements are faulty and can be easily checked with a tester.

How to check the LED?

If we are talking about an LED, the check algorithm is similar, but the task will be further facilitated by the fact that when turned on directly, this type of diode will glow. Of course, this will make it possible to finally make sure that he is okay.

But it happens that it is necessary to check the zener diodes. A zener diode is a type of diode; its main purpose is to maintain a stable output voltage regardless of changes in current level.

Unfortunately, a dedicated function for testing this type of electronic elements has not yet been implemented in multimeters. Nevertheless, you can often ring them using the same principle as with diodes. But many experienced radio amateurs say that checking the zener diode using a digital tester is very problematic. The reason for this is the fact that the voltage of the zener diode must be lower than the voltage at the outputs of the multimeter. This is due to the fact that due to low voltage, it is possible to consider a faulty model to be working, and the accuracy of the readings decreases.

If when checking a diode it is necessary to pay attention to the value of the breakdown voltage, in the case of zener diodes the resistance will be indicative. This figure should be between 300 and 500 ohms. And similar to the algorithm for dealing with diodes:

If current is passed in both directions it is called breakdown,
If the resistance is too high it is a break.

It is also important to remember that the digital value when ringing a zener diode will be higher than the value of conventional diodes. If you need to distinguish one element from another, such a check will help.

How to check zener diode

Zener diodes, the testing of which did not bring the desired results, are often tested by inventors using additional devices, sometimes constructing them themselves. One of the simplest ways is to use a power supply with the ability to switch voltage to test. You must first connect a resistor with a resistance value that is optimal for the zener diode to the anode, and then connect the power supply. Then the voltage on the diode is measured and raised in parallel on the block. Upon reaching the stabilization voltage level, this figure should stop growing. In this case, the zener diode is normal; if there is any difference from the above circuit, it is faulty.

elektro.guru

How to check an LED with a multimeter without desoldering it from the circuit

Testing this semiconductor-class radio component does not present any particular difficulties. The only difference is that some devices in this group need a power supply of 1.5 V (a number of red and green low-power ones) to glow, others a little more - about 3.3 ± 0.3. The difficulty is that to test the LED you will have to unsolder it, and this is not always possible (given the density of the circuit layout) or advisable (for example, due to time constraints). What can you do?

The solution is simple - make special devices, since the standard probes that come with the multimeter are not suitable for these purposes. They will be needed (for example, from an old device), but only after some “modernization”.

Method 1

What to cook:

A small fragment of PCB, literally a piece, but always with double-sided foil. A “spot” of solder must be applied to each so that in the future you can easily fix the wires and leads of the device for testing the LED.

Probes from the multimeter, from which you should cut off (or unsolder, and then restore everything) the plug. The free ends need to be cleaned and tinned, that is, prepared for soldering.

Paper clips – 2 pieces. They are given a shape that is clearly visible in the figure below. These will be the terminals of the device (analogous to plugs) that are connected to the multimeter. Although this is not the only option. Instead of paper clips, you can use flexible steel wire by cutting a couple of pieces of the required length. The main thing is that these leads are slightly cushioned, then it will be much easier to connect them to the multimeter socket.

Soldering acid. Using traditional pine flux is futile. The paper clips are made of steel, so the usual method for securely fixing them on PCB is of little use.

Soldering iron. Power – at least 65 W. Trying to secure a paper clip to the board with a mounting tool (24, 36 W) is a waste of time. You will need to lay the melt in a relatively thick layer, and a low-power (miniature) soldering iron is useless in this case.

Multimeter. These household appliances are available in several modifications. Their main difference is in functionality, that is, the ability to measure certain parameters of the circuit and parts. You will need a multimeter that can test transistors.

In principle, everything you need to make a simple device for checking an LED with a multimeter is always at hand. In the end it should look something like this.

In order not to be confused with the polarity of connecting the probes to the LED, the terminals of the device should be slightly shifted from the center line. Then it’s easy to remember where the conditional “+” and “–” are.

Checking the LED

You need to plug the “contacts” of the device into the plug for testing Tr (the anode terminal is on connector E, the cathode terminal is on C), put the multimeter switch in the “Transistor measurement” (hFE) position and attach the probes to the board at the points where the pins are soldered /p of the device (from the front or back side, as is more convenient). If it is working properly and the polarity is correct (plus to the anode), it will begin to glow.

Method 2

It is much simpler, and if the layout of the circuit allows, and the legs can be reached, then the LED is checked using the probes of any multimeter in the same way as for testing resistance. This is discussed in detail here.

That's all, nothing complicated. This technology has been tested many times, and not a single LED failed during such testing.

electroadvice.ru

How to check a diode? - Diodnik

When starting to check the diode for performance, you need to understand that visually a faulty diode is sometimes virtually impossible to distinguish from a working one. We will tell you in detail how to check the diode in our article.

Also, before checking, you need to know that the main malfunctions of diodes are of three types:

diode breakdown (the most common defect). As a result of such a defect, the diode conducts current in any direction, without actually having its own resistance:
diode breakage (in practice, this occurs less frequently). In this case, such a diode stops completely conducting current, regardless of the direction of current flow.
leakage. In this case, the diode conducts a slight reverse current.

How to check a diode with a multimeter?

Whenever checking diodes, it is best to completely desolder them from the main circuit.

The experimental diode 1n5844 is a 5A Schottky diode. The test is carried out with a Unit 151B multimeter. Any diode has two terminals: a cathode and an anode. The cathode is marked with a silver stripe.

In order for current to flow through the diode, a positive voltage must be supplied to the anode and a negative voltage to the cathode. Having turned on the required measurement mode on the multimeter, you can begin checking the diode.

It must be remembered that a working diode only conducts current in one direction.

Having connected the probes to the anode (red +) and to the cathode (black -), we see the values on the display - this is the threshold voltage of the diode. From this we can conclude that the pn junction is open.

Having connected the probes to the cathode (red -) and to the anode (black +), there are no values on the display except 1.

This completes the diode check procedure - the diode is working.

If, regardless of the polarity of the diode connection, the device shows the value 0 or 001 (and sometimes we hear a characteristic sound signal), this indicates that the diode is broken. Such a diode conducts current in any direction. If, regardless of the polarity of the diode connection, the device displays the value 1, such a diode has an open circuit. It doesn't conduct current at all.

How to check a diode if you don’t have a multimeter with a diode test function at hand? You can use a regular ohmmeter for this purpose. Having set the measurement limit value to 20 kOhm, the diode is checked with such a tester according to the scheme described above.

Sometimes you may encounter dual diodes. Such diodes have three terminals; two diodes are contained in one housing. They have a common anode or cathode. Checking such a dual assembly is absolutely no different from checking a regular diode, you just need to check each diode in the assembly. Read more about how to check a Schottky diode in this article.

Classmates

Comments powered by HyperComments

diodnik.com

types and features, testing instructions, determining the operability of the bridge

It's sad, but you need to start with theory. You will have to study the types of diodes, area and purpose of application. Without delving into the physical foundations of electronics, let's go through the search queries. It is important to understand that all diodes are united by the ability to pass current in one direction, blocking the movement of particles in the opposite direction, forming a kind of valves. Then we will discuss how to test a diode with a multimeter.

Types of diodes

So, diodes pass current in the forward direction and block it in the reverse direction. On electrical diagrams, diodes are indicated by black arrows bounded by a crossbar. The symbol shows the direction of the current in the physical sense - the directional movement of positive particles. To create a forward current, a negative potential is applied to the end of the arrow, and a positive potential is applied to the beginning. Otherwise, the diode will be in a “locked” state.

When electrons move due to the imperfection of the molecular lattice, heat is lost, which entails a voltage drop in the forward direction. Silicon diodes have a higher direct potential, germanium diodes have a lower one. Schottky diodes are characterized by a smaller potential drop due to the replacement of one semiconductor layer with a metal one, i.e. there is no p-n junction. The loss current increases, and the voltage drop across the open switch in the forward direction is record low.

The effect is not typical in all voltage ranges. Schottky diodes are most effective at voltages equal to tens of volts. They are used in output filters of switching power supplies. Remember: the voltage ratings of the system unit are 5, 12, 3 V. The method of constructing circuits using a Schottky diode is typical.

A popular type of diode is a zener diode. Its working area is the breakdown area. Where a conventional diode fails, a zener diode protects the equipment. The process is characterized by an increase in voltage to nominal and a sharp stabilization. Through zener diodes, sensitive and weak microcircuits of switching power supply controllers are powered from high-voltage lines so that they cut the voltage into pulses of large amplitude. Without zener diodes, powering microcircuits is solved using extremely complex methods.

When evaluating a Zener diode using a multimeter, take into account that the working area is the reverse branch. Technically, the breakdown voltage for testing is obtained from batteries connected in series, then the presence of stabilization is checked. Direct connection of a zener diode is used extremely rarely; ringing in the traditional way is a bad idea. Zener diodes also include an avalanche diode, where the impact ionization effect is used to stabilize the current.

Diode designation on diagrams

It happens that the specifics of the device are not clear. The printed circuit boards are marked - each element has a strictly defined designation, and the powerful diodes of the rectifier bridge cannot be confused with a tiny glass zener diode. The worst option is a tangle of conductors with unknown elements: either a diode, or an unusual type of resistor, or an exotic capacitor.

When faced with a similar situation, they carefully take an enlarged photo, then search the Internet using the image. Although the markings of zener diodes are illegible, it is possible to find information on the Internet. This step greatly speeds up the process of identifying and assessing the performance of the device.

An infrared diode is checked with a multimeter in the same way: we remove the forward voltage, then make sure that there is no reverse current flowing. To check the glow, use the viewfinder of a night video camera. It directly registers the infrared radiation of objects. A working IR diode is visible in the viewfinder - like a star. They check the glow with thermal imagers and night vision devices, being careful: the radiation power of light and IR diodes is high, comparable to the power of laser radiation.

The inscription inside the printer about the presence of a laser cannot be considered a joke. And neglect her. Keep your retina away from the infrared diode.

Diode test circuit

How to check a diode using a tester

To test diodes, multimeters are equipped with a special scale marked with the corresponding icon - a schematic designation of a diode. When the mode is turned on, low resistances turn on the buzzer, high ones are characterized by the nominal value or the voltage dropping across it. Based on the readings, they judge the characteristics of the diode, for example, the resistance of direct connection.

To correctly interpret the readings, it is important to take into account the characteristics of the tester: constant voltage and low nominal voltage used for evaluation. Example: when measuring resistance, the tester passes current through it, applying a certain voltage to the probes. Any multimeter model is characterized by unique parameters. The voltage is recognized by the charge of the capacitor: turn on the multimeter in the ringing or diode testing mode, after a short time a potential difference will form on the capacitor plates. Measured using the standard scale of the tester. The value ranges from hundreds of millivolts (fractions of a volt) to units of volts.

Knowing the voltage applied to the diode, the accuracy of the reading is verified using its current-voltage characteristic. Enter a search query on Yandex and get acquainted with the full technical documentation for the element being studied. Then they place an abscissa ruler at the right place on the scale to find the output current. Using Ohm's formula, the open state resistance is calculated: R = U/I, where U is the auxiliary voltage generated by the tester. Compare the value found from the graph with that indicated on the display.

This is one of many techniques. It is important to know how to find the right paths, analyze and compare data. The first step is to search for generalized information: what diodes are, their characteristics (primarily current-voltage), the intricacies of the operation of a particular device. Knowing the theoretical foundations, it is easy to operate with information and draw correct conclusions from research results.

Let's move on to a real-life example: let's examine a diode bridge from a car generator!

How to determine the performance of a diode bridge

A car needs electricity - for air conditioning systems (along with engine energy), wipers, exterior and interior lighting. Constantly loading the battery, which is done while parked, is not economical. The problem is solved by connecting a synchronous alternating current generator to the motor shaft. Previously we used a collector circuit. But the brushes do not tolerate shaking, and there was a need for frequent maintenance.

Three-phase generators are now being installed. Because the revolutions constantly fluctuate, the constancy of the output characteristics is maintained by changing the rotor feeding current. As a result, the strength of the alternating magnetic field of the stator monitors every change in the operation of the motor. The price to pay is instability of the output voltage. It is rectified and filtered using a Larionov diode bridge circuit.

Deep technical details are redundant, we will limit ourselves to light knowledge:

For any method of connecting the generator windings, there are three output points. Each is connected to ground through a diode in the negative half-cycle, and to consumers of the car network - in the positive half-cycle.
In total, there are six diodes.
The bridge consists of two crescent-shaped planes isolated from each other, made of durable alloy. There are three diodes on each, electrical connections are made according to the diagram (see figure).

Connection diagram for a three-phase diode bridge

From the diagram you can see:

Three diodes are connected in pairs with zero resistance between the cathode (negative polarity) and the anode (positive polarity). The generator terminals go here.
Two triplets of diodes (lying in the same crescent-shaped plane) call each other as cathodes or anodes. Depending on which electrode produces a short circuit, the branch is determined - load or going to ground.

Having created the correct electrical connection layout, they begin checking each diode individually. The branch going to ground is tested from the generator side, the other from the load side. The direction is known from Larionov's scheme. We check the diode bridge with a multimeter, touching the base of the black arrow (see figure) of each element with a red probe, and the tip of the same element with a black probe. At the same time, check the insulation of contacts with crescent-shaped planes, incl. neighboring. Based on the data obtained, the need to continue troubleshooting is assessed.

Conclusion: the diode, without desoldering, is checked with a multimeter on a rough structure like a car generator bridge. Ringing an electronic board is more difficult. Any check is carried out with specially shaped probes. For rough designs, use crocodile grips, and check the motherboard with thin needle-shaped probes. In the latter case, there is a chance to test the diode with a multimeter on the board under voltage with the risk of burning the tester.

We hope that the reader now understands how to test a diode with a multimeter.

vashtehnik.ru

Checking the zener diode on the board with a multimeter

Every radio amateur knows how sometimes it is important to know whether a particular radio component is working or not. Last but not least, this applies to zener diodes. A multimeter is used as a tester to check electrical components for the presence of stabilization voltage.

The suitability of electrical components is determined by a multimeter

Zener diode and its properties

For electronic circuits to operate, stabilized voltage readings are needed at the output. They are obtained by including semiconductor zener diodes in the circuit, which give the same output voltage, independent of the amount of electric current passed. Without these elements, many low-current systems do not work. For example, almost every radio amateur has soldered the l7805cv voltage stabilizer or its analogues at least once in his life.

Zener diode helps stabilize voltage

Zener diodes have nonlinear current-voltage characteristics; in properties, as well as in appearance (in glass or metal), they resemble a conventional diode, however, their tasks are somewhat different. Zener diodes are connected to the circuit in parallel with the consumer and, if the voltage rises sharply, the current flows through the zener diode, and the voltage in the network is equalized. If a strong current is applied for a long time, thermal breakdown occurs.

Check procedure

In order to determine whether a given zener diode is suitable or has failed, the multimeter must be switched to the mode that tests diodes (or to the ohmmeter mode) - checking zener diodes using the ringing method is carried out in the same way.

The multimeter probes are connected to the zener diode terminals and the indicator readings are observed. The check should be carried out in two directions:

the positive probe of the device touches the cathode of the part - the indicator shows infinite resistance;
the multimeter is connected to the anode of the zener diode - the resistance in units or tens of ohms (voltage drop) will be displayed on the screen.

Such indicators appear because a working zener diode (like a regular diode) is capable of conducting only unidirectional electric current, and the test should not cause a short circuit in the network.

Checking a working zener diode with a multimeter

If, when ringing in both directions, the multimeter shows infinite resistance, the zener diode is defective, since the electron-hole junction is broken and no current passes through the electrical component.

Picture when checking a non-working zener diode

Pay attention! It sometimes happens that when measuring a zener diode with a multimeter, a resistance of several tens or hundreds of ohms is produced in both directions. In the case of conventional diodes, this position indicates that the part is broken. However, this is not true for a zener diode, because it has a breakdown voltage: when the multimeter probe comes into contact with the ends of the zener diode, the internal power supply voltage of the measuring device is affected. If its voltage is greater than the breakdown voltage, then multi-ohm resistance indicators will appear on the indicator.

So, when the multimeter battery voltage is 9 volts, zener diodes with a voltage below this value will indicate a breakdown. Therefore, experts do not recommend testing zener diodes with low stabilization voltage using digital multimeters. For these purposes, a good old analogue tester is better suited.

An old-style analog tester will help you check low-voltage zener diodes, avoiding breakdown

How to check the zener diode on the board

If the zener diode is soldered into the board, then the procedure for checking it does not differ from that used for a free electronic device of this type.

Important! When measuring and repairing the board, be sure to follow safety precautions to protect against electrical shock. When ringing a soldered zener diode, all other elements, except the one being tested, can produce greatly changed indicators; this must also be taken into account.

If, when checking on the board, questionable results are obtained regarding the suitability of the zener diode, then it is worth unsoldering it and checking only this element with a multimeter, isolating it from the influence of other parts of the circuit. You can also sometimes use an attachment for a multimeter, which you can solder with your own hands from available parts.

It is advisable for every radio amateur to know how to test a zener diode with a multimeter - this will help assemble working circuits and save radio components by identifying non-working ones. However, with such a check it is impossible to obtain a 100% reliable result. The suitability of a zener diode can only be guaranteed by its inclusion in the electrical circuit: if the device works, then the stabilizing element is functioning.

Video

elquanta.ru

How to test a diode with a multimeter - detailed instructions

Diodes are popular and widely used electronic elements with varying levels of conductivity.

Before you check the diode with a multimeter (test the diode and zener diode with a tester), you need to know the features of such a testing device and the most important rules for its use.

Classification

Diodes are electrical converting and semiconductor devices that have one electrical junction and two p-n junction outputs.

The currently generally accepted classification of such devices is as follows:

in accordance with their purpose, diodes are most often rectifier, high-frequency and ultra-high-frequency, pulse, tunnel, reverse, reference type devices, as well as varicaps;
in accordance with the design and technological characteristics, diodes can be represented by planar and point elements;
in accordance with the source material, diodes can be germanium, silicon, gallium arsenide and other types.

In accordance with the classification, the most important parameters and characteristics of diodes are presented:

maximum permissible indicators of reverse DC voltage level;
maximum permissible indicators of the reverse voltage level of the pulse type;
maximum permissible indicators of direct current of direct type;
maximum permissible indicators of direct current of pulse type;
rated direct current direct current;
direct current voltage of a direct type under rated conditions, or the so-called “voltage drop”;
direct current of the reverse type, indicated under the conditions of the maximum permissible reverse voltage;
spread of operating frequencies and capacitance indicators;
breakdown voltage level;
level of thermal housing resistance, depending on the type of installation;
the maximum possible indicators of dissipative power.

Depending on the power level, semiconductor elements can be low-power, high-power or medium-power.

When choosing a diode, you need to remember that the symbol of such elements can be represented not only by standard markings, but also by UGO applied to electrical circuits that are of fundamental importance.

Checking the rectifier diode and zener diode

In terms of independent diode testing with a multimeter, the following is of particular interest:

conventional diodes based on p-n junction;
Schottky diode elements;
Zener diodes that stabilize the potential.

Conventional testing, in this case, can only determine the integrity of the pn junction, and it is for this reason that in such devices the operating point must be shifted.

Diagram of the simplest method for checking zener diode voltage

It is enough to use a simple circuit that includes a conventional power supply and a resistor to limit the current. For non-standard testing, a multimeter is used to measure voltage under conditions of a smooth increase in the supply potential.

If, under conditions of increasing supply voltage, a constant potential difference is observed, as well as a potential difference equal to the declared values, then the diode device is considered to be working and cannot be replaced.

Circuit assembly

The standard scheme, carried out through wall-mounted installation, consists of several main elements, presented:

16-18 V power supply;
1.5-2 kOhm resistor;
digital or pointer voltmeter;
device being tested.

How to test a Schottky diode with a multimeter

A feature of some multimeters is the presence of a “diode test” function. Under such conditions, the instrument displays the actual diode forward voltage at current conduction.

A tester equipped with a special function registers a slightly underestimated level of forward voltage, which is due to the insignificant current value that is involved in the test.

In the store you can find a variety of LED lamps for the home. Not everyone knows how to choose a quality device. If interested, read the detailed information.

Instructions for assembling an LED flashlight with your own hands are presented here.

Many people throw away an LED lamp if it breaks. In fact, most of these devices can be repaired. You can read everything about repairing LED lamps at this link.

Setting up the multimeter

Testing a semiconductor element using a digital multimeter will require switching the device to diode test mode. An alternative option, if there is no switching to the “diode test” position, is testing in resistance mode, with a range of no more than 2.0 kOhm.

In this case, a direct connection is made: the red wire is connected to the anode, and the black wire to the cathode. With this setting of the multimeter, measurements show a resistance equal to several hundred Ohms; in the opposite direction, an open circuit is detected.

Multimeter UNI-T

It should be noted that different types of diode devices can differ significantly in terms of forward voltage.

For example, germanium devices are characterized by a voltage in the range of 0.3-0.7 V, and for silicon elements values of 0.7-1.0 V are acceptable.

As practice shows, some types of testers, when testing diode elements, show lower values of the forward voltage level.

Less common dual diodes are distinguished by the presence of three terminals and a common anode or cathode in one housing, but testing such elements is no different from testing a standard diode device.

Turning on the power supply

If checking the performance of diodes with a multimeter involves switching the tester to the “diode” icon position with connecting the black probe to the “COM” terminal and the red one to the “V ΩmA” terminal, then the presence of a power supply is to identify the following problems:

connecting the unit is accompanied by a “jerking” of the fan power supply, stopping, lack of output voltage and blocking the power source;
connecting the unit is accompanied by voltage ripple at the output and protection is triggered without blocking the power source.

AC current measurement

Quite often, a sign of a leak in Schottky diodes is the spontaneous shutdown of the power supply. It is also very important to consider that incorrect circuit design on power supplies can cause leakage of diode rectifiers and overload of the primary circuit.

Testing consists of setting the measurement limit to a value of 20 K, and measuring the reverse diode resistance. With this method, a working diode shows an infinitely high resistance level on the device.

Connecting a multimeter

The main, most common diode faults can be presented:

breakdown, accompanied by current conduction regardless of direction, as well as the actual absence of resistance;
a break accompanied by a lack of current conduction;
leakage accompanied by the presence of a slight reverse current.

The procedure for setting up the device for verification and sequential testing is very simple.

The connection of the anode and the multimeter probe to “+”, as well as the cathode and p-n junction to “-” must be open. In this case, the device emits a characteristic sound signal. The reverse connection option with a closed p-n junction is indicated by one.

Did you know that LED lamps can have different designs? Design of 220 Volt LED lamps - types of devices and assembly methods.

Instructions for replacing fluorescent lamps with LED lamps are presented here.

As the practice of independent testing shows, the passage of current, regardless of the connection polarity, most often accompanies a short circuit, and the absence of continuity in both directions is observed when there is a break in the circuit.

Video on the topic

proprovoda.ru

How to properly check a diode bridge with a multimeter

There is a diode bridge in almost any equipment, and its failure is a very common reason for the breakdown of an electronic device. Checking and replacing the diode bridge in a workshop is unreasonably expensive. Nevertheless, you can independently identify the malfunction of the rectifier unit and, if necessary, repair or replace the bridge yourself at minimal cost. To do this, you need to know how to check the diode bridge. This is exactly the problem we will try to solve today.

What is a diode bridge and what's inside it?

Before we start checking the diode bridge, we need to know what a diode bridge is and what it consists of. A bridge is a circuit made up of four diodes connected in a certain way and serves to convert alternating voltage to direct voltage. This circuit is used in almost all equipment powered from the network - after all, almost all electronics need constant voltage for their power supply, but in the network it is alternating. But first, let's find out what a diode is and what properties it has.

Diode and its operating principle

A diode is a two-electrode semiconductor device capable of conducting current in only one direction. It is often called that - a semiconductor. If you connect a semiconductor to a DC circuit with the anode to the positive terminal of the power source, current will flow through it. If to negative, there will be no current in the circuit. In the second case, the diode is said to be closed. Now let's connect our semiconductor to an alternating voltage circuit.

AC voltage rectification using semiconductors

The figure clearly shows that the semiconductor passed the positive half-wave and cut off the negative one. If you turn it on in a different polarity, the positive half-wave will be cut off.

Why is a diode bridge better than a diode?

Theoretically, using just one semiconductor, you could convert AC voltage to DC. In practice, you will get a highly pulsating voltage at the output, which is of little use for powering electronic circuits. But if you turn on several diodes in a certain way, then you can not cut off the extra half-wave, but literally turn it over. Now look at the diagram below:

Diode bridge according to the Graetz circuit

With a positive half-wave, diodes numbered 1 and 3 operate: the first passes the plus, the second - the minus. Semiconductors 2 and 4 are locked at this time and do not participate in the process - a reverse voltage is applied to them, and the resistance of their pn junctions is high. With a negative half-wave, diodes 2 and 4 are switched on. The first redirects the negative half-wave to the positive output, the second serves as a minus. At this stage, devices 1 and 3 are locked. As a result, the negative half-wave does not disappear, but simply turns over:

The result of the bridge rectifier

This is how, with the help of three additional semiconductors, we doubled the rectification efficiency. Of course, the output voltage is still pulsating, but a smoothing capacitor of relatively small capacity can easily cope with such pulsation.

Back to contents

How to find a diode bridge on a board

Before ringing the diode bridge, you must first find it on the board. To do this, of course, you need to know what it might look like. Its appearance depends on the type of case. Rectifiers can consist of either four separate semiconductors soldered side by side, or diodes assembled in one housing. Such a prefabricated device is called a rectifier assembly. Here are just a few types of such assemblies:

Appearance of the rectifier diode assembly

Despite the abundance of forms, it is not difficult to recognize an integrated diode bridge. It, as you noticed, is four-pin, and its two pins are marked with “+” and “-” signs. This is the rectifier output. The input terminals are supplied with alternating voltage, so they are designated by the symbol “~”, the letters “AC” (an abbreviation for “alternating current”), or may not be designated at all.

The diode bridge is located next to the AC voltage supply wires: from a transformer or for switching power supplies directly from the outlet (power cord).

Expert opinion

Alexey Bartosh

Ask a question to an expert

As a rule, a smoothing electrolytic capacitor is placed next to the rectifier - such a relatively large barrel.

In the figures below, rectifier diode bridges are indicated by a green arrow:

Examples of the location of rectifier diode assemblies and bridges on discrete elements to contents

How to check a diode bridge

There are two ways to check the diode bridge:

Using a tester (multimeter).
Using a light bulb.

The first method, of course, is preferable: it is very accurate and safe for a diode bridge. But if there are problems with the multimeter, then you can use a lamp from a flashlight and a 5-12 V battery.

Now if the diode bridge is found, first of all you need to conduct an external inspection of the entire device board. Elements must have a natural color and not be charred or destroyed. Inspect the soldering area and the integrity of the tracks: it is important that nothing comes unsoldered or bursts. At the same time, carefully inspect the electrolytic capacitors (those barrels). They should also be in order: not damaged or swollen. If any capacitor swells or explodes, it must be desoldered - it will still require replacement so that it does not interfere with measurements.

If the capacitor explodes, after dismantling it, the entire board must be thoroughly washed with alcohol. The scattered parts of the capacitor are an electrolyte that not only conducts current, but also has the properties of an acid.

Diode bridge continuity test using a tester

Now we move on to checking, or, as they say, testing the diode bridge, which often has to be carried out in two stages:

Pre-call on site.
Accurate check.

The first stage is convenient because you don’t have to solder the diode bridge, but check it directly in the circuit. The second method is more labor-intensive, but if the first option fails, it will help to conduct an accurate check.

To work, we need a tester: pointer or digital. In the first case, the device must be able to measure resistance, in the second, it must have a semiconductor testing mode. This mode is indicated by a diode icon:

You can check the diode bridge only in this switch position

Expert opinion

Alexey Bartosh

Specialist in repair and maintenance of electrical equipment and industrial electronics.

Ask a question to an expert

Never test semiconductor devices with a digital tester in resistance measurement mode. In this mode, almost all such devices carry out alternating current measurements, and semiconductor testing will not show anything.

Testing the diode bridge in place

So, we switch the pointer device to resistance mode with a measurement limit of about 1 kOhm, and turn on the digital one to check the diodes. Now let’s remember the diode bridge circuit:

Electrical circuit of the diode bridge

Your task is to ring each of the diodes by connecting the tester probes to it, first in one and then in the other polarity. As can be seen from the diagram, it is not difficult to get to each diode individually; you just need to select the appropriate legs of the assembly. If the rectifier is assembled on separate semiconductors, there is no problem at all: just ring each one by touching its terminals with the probes of the device.

What do the measurements say after the call? For each of the individual semiconductors, the measurement result should be as follows: in one direction the tester shows a small resistance (value of about 200-700 Ohms), in the other it is impossible to ring at all - the device shows “infinity”.

Expert opinion

Alexey Bartosh

Specialist in repair and maintenance of electrical equipment and industrial electronics.

Ask a question to an expert

In fact, a digital tester in diode testing mode does not show the circuit resistance, but the magnitude of the voltage drop across the open diode. This is of great importance for measuring the parameters of semiconductors, but is not at all significant for continuity. Thus, the algorithm for working with any type of tester is the same, and the drop voltage can be taken either as millivolts or as Ohms.

If it’s difficult for you to independently calculate each of the diodes based on their terminals, then take a look at the picture below, which shows the continuity of the GBU25M diode assembly as an example.

Testing the diode bridge using a multimeter

Please note that the numbers on the screen of the tester shown in the figure are relative. The diode's voltage drop and resistance can fluctuate and depend on the type of semiconductor and its operating voltage.

Accurate check

If the results of your measurements coincide with those that I described, then the diode bridge can be considered serviceable. But if something went wrong and you did not get the desired results, then the diode bridge will have to be unsoldered and checked again. The fact is that most circuit solutions involve “tying” the rectifier with additional elements: capacitors, filters, coils, etc. All this can distort the measurements, and you simply won’t see why and what’s wrong.

Turn on the soldering iron and solder the diode bridge. If it consists of individual diodes, then it is enough to unsolder them only on one side, lifting one leg of each diode above the board. Now take another measurement. The technique is the same as in the first case: ring each of the diodes in both directions, changing the polarity of connecting the device probes.

If even now the readings of the device do not correspond to the norm, we can say with complete confidence that the assembly or a separate diode is faulty. If there are high resistance values in both directions of measurement, the diode junction is burnt out, it is open. It rings in both directions - the diode is broken, short-circuited. If the diode assembly is broken, you will have to replace it entirely. If the diodes are separate, it is enough to replace the faulty device with a similar one.

Expert opinion

Alexey Bartosh

Specialist in repair and maintenance of electrical equipment and industrial electronics.

Ask a question to an expert

The Internet is full of search queries like “how to check a diode bridge with an indicator screwdriver.” An indicator screwdriver, or more precisely, a voltage indicator, is intended for completely different purposes, and checking diodes with it is not only pointless, but also dangerous!

Testing the bridge with an indicator lamp

If you don’t have a multimeter at your disposal, then to check the diode bridge you can get by with improvised means: a light bulb and a battery. You will need a battery or a cassette with several AA batteries with a total voltage of 5-12 V and a low-power incandescent light bulb with approximately the same supply voltage as the battery.

The lamp must be of minimum power so as not to burn the diode with an excessively high current. For example, a light bulb from a low-power flashlight will do. If you use a 12 V battery as a battery, then a light bulb from the dashboard illumination or side headlights (“sidelights”) will also work.

You, of course, remember that a diode conducts current in one direction, so take a look at the two circuits I proposed:

Scheme for checking a diode using an incandescent lamp

In the diagram on the left, the diode is turned on in the forward direction and passes current - the lamp should light up. In the right figure, the diode is turned on in the opposite direction and does not pass current - the lamp is extinguished. Got the idea? Assemble the tester and use probes A1 and A2 to ring the diode bridge, focusing not on the multimeter screen, but on the lamp. On - low resistance, off - high resistance. That's the whole trick.

Back to contents

Checking the car generator diode bridge

If you have a car, then you will probably be interested in this section of the article. The failure of a car generator is a serious problem, the solution to which costs a lot of money. But even here, the cause of the breakdown may be a malfunction of the rectifier bridge diode, which is installed in the generator. This means that you can try to resolve the issue on your own. Let's take a look at a simplified generator circuit:

Car generator diode bridge circuit

In front of you is the same diode bridge, only three-phase, with six rather than four diodes. This means that calling it will not be difficult!

So, disassemble the generator and remove the diode bridge, which looks something like this:

Diode bridge of a car generator

I marked the power diodes with green arrows, but there are also three auxiliary ones, they are marked with red arrows. We will call both of them - everything is in sight and easily accessible.

Rinse the shoe in gasoline to remove all dirt and oil that may be causing the problem. When the bridge is dry, start ringing each diode using the technique described above. For work, you can use both a multimeter and a lamp from the dimensions complete with a car battery.

Expert opinion

Alexey Bartosh

Specialist in repair and maintenance of electrical equipment and industrial electronics.

Ask a question to an expert

Pay attention! Diodes located on different horseshoes are only identical in appearance. In fact, some have an anode at the central terminal, others have a cathode. This is done so that the diodes can be placed on one horseshoe, which simultaneously acts as a radiator, without insulating spacers.

Back to contents

Safety precautions

The vast majority of modern equipment has switching high-voltage power supplies. This means that the diode bridges in them operate at a voltage of up to 300 V. Therefore, before you start measuring, disconnect the device from the network and, most importantly, discharge the smoothing electrolytic capacitors, which can “hold” a life-threatening charge for hours. For clarity, I marked them with red arrows:

PC power supply board with diode bridge and smoothing capacitors

To discharge them, short-circuit the capacitor terminals for a second with a screwdriver, holding it by the insulating handle. Otherwise, you will not only burn the multimeter, but you may also be exposed to lethal voltage.

And the last piece of advice: after repairing the device, do not rush to plug the power plug into the socket. To begin with, plug it into the network through an incandescent lamp with a power of 150-200 W. If done correctly, the lamp will barely glow. The lamp will signal you about a failed repair with a bright light at full intensity, indicating a short circuit.

When making all kinds of network switches, take care of your eyes. If repairs are unsuccessful, many elements of switching power supplies can explode no worse than a fragmentation grenade. And the rupture of an electrolytic capacitor, as I wrote above, threatens a huge scattering of not only fragments of aluminum and scraps of paper, but also splashing acid.

So you learned how to check the serviceability of diode bridges. I hope that in the future this knowledge will be useful and will save not only your money and time, but also your nerves. Carrying out independent troubleshooting of an electronic device and then repairing it is cool. Isn't it? Write your answer in the comments

How to check an LED lamp, strip and other lighting devices for the serviceability of LED elements. Despite their longer service life compared to incandescent lamps, lighting LEDs fail faster than indicator lamps.

LEDs are semiconductor devices that create optical radiation when electric current passes in the forward direction. They are divided into two types - indicator and lighting. The former are characterized by lower power, therefore they are used in the illumination of electronic devices, performing the function of indicators. The latter are used in lighting devices, including lamps, strips, lanterns and spotlights.

Checking LED lamps

Four main characteristics of light-emitting diodes (LEDs) are important - operating current, forward voltage drop, power and luminous flux. The operating current is individual for each product and is indicated on the housing. With voltage drop, everything is much simpler - its value depends on the color and material from which the device is made.

Typically, the dependence of voltage on LED color is as follows:

red - 1.5-2 V;
orange and yellow - 1.8-2.2 V;
green - 1.9-4 V;
blue and white - 3-3.5 V;
white, blue and green - 3-3.6 V.

Important! All parameters are measured with a multimeter. And you don't need to be a qualified electrician to do this!

Another way to test a light emitting diode (LED) is to connect it to a power source consisting of batteries. Among the available tools used in troubleshooting, we highlight chargers for mobile phones (or more powerful ones for flashlights).

Checking with a multimeter

When using a multimeter, follow these steps:

Turn the toggle switch to the LED diode test mode.
Connect the multimeter leads to the LED.
Make sure to maintain the polarity of the LEDs: red ones are powered by the anode, black ones by the cathode.

If connected correctly, the device will light up, otherwise the readings on the multimeter will not change.

Determine faults with minimal lighting to increase the likelihood of detecting the LED glow. If it is absent, rely on the multimeter indicators - on a working element, the value should be different from the default readings.

There is a simpler method - ringing LED diodes. A multimeter is used to test transistors. In the PNP section, connect the cathode to hole C and the anode to E.

Checking with improvised materials

To detect faults in LEDs, an LED tester is used, made from improvised means - several AA batteries connected in parallel, or a powerful “Krona”.

The tester is also assembled from an unnecessary charger for a phone or other electrical device. Cut the connector at the end of the cord and strip the wires. Connect red (plus) to the anode, and black (minus) to the cathode. If there is enough voltage, the LED will light up.

Flashlight chargers are useful if a light bulb or strip with more powerful LEDs is faulty.

Checking LEDs without desoldering

To connect the multimeter probes, connect them by soldering to a small metal object - a paper clip. Install a textolite plate between them, insulating it with adhesive tape. This simple design is a safe guide for securing probes. Connect to the LED without desoldering it from the circuit.

Checking the serviceability of the LEDs in the flashlight

Before troubleshooting, remove the battery from the flashlight, disassemble it and remove the textolite board to which the required LED is attached. Use the tester by connecting probes to it via the PNP connector. It is not necessary to solder the diode - measurements are taken on the board. The device will light up only when turned on directly!

When connecting LEDs in parallel, measure the resistance of the entire circuit. If it is close to zero, then one of the semiconductors is not working correctly. To determine which one, use the method indicated above, studying each SD separately.

Checking the LED spotlight

Visually inspect the LEDs. If you see a large yellow square, then do not try to check the functionality with a tester - the voltage of such an element is over 20 V.

If the spotlight uses several small SMDs, then it makes sense to use a multimeter. Disassemble the device and find the backlight driver, moisture-proof gasket and board with installed LED diodes. The procedure is similar to checking an LED lamp (read above).

Checking the infrared diode

Infrared diodes are used in many electronic devices, and are especially popular in remote controls. Their main function is to transmit a signal to the photoreceiver of a TV, music center or LED lamp. If the batteries are good, then the LED has failed.

It is unrealistic to see the glow of an infrared LED without available tools, but checking it is simple. Point the camera (or the camera of any device) at the LED located in the remote control. If the semiconductor is working, you will see a short glow with a purple tint.

An oscilloscope is also used as a tester for such LEDs. If IR radiation hits its photocell, voltage is created.

Checking the LED strip

LED strip is a light source made from several LED elements. SDs are grouped in groups of three per site. Then the tape can be divided into segments of any length without compromising its performance characteristics.

To make sure it works, apply electric current to the contacts. The whole thing will light up if it is working properly. If only part is lit, the problem is in the conductive cable. It needs to be checked with a multimeter.

If a whole section of three LEDs does not light up, the problem is in these elements. Inspect each of them and measure the resistance of the resistor of the entire group.

The considered methods for checking LED diodes in lighting fixtures are simple - arm yourself with a multimeter or wires with a pair of AA batteries. If you find a faulty element, replace it or take it to a workshop.

Among home craftsmen and craftsmen, there is periodically the need to determine the performance of a thyristor or triac, which are widely used in household appliances to change the speed of electric motor rotors, in power regulators for lighting devices and in other devices.

How a diode and thyristor work

Before describing the testing methods, let us recall the design of a thyristor, which is not for nothing called a controlled diode. This means that both semiconductor elements have almost the same structure and operate in exactly the same way, except that the thyristor has the limitation of being controlled through an additional electrode by passing an electric current through it.

The thyristor and diode pass current in one direction, which in many Soviet diode designs is indicated by the direction of the triangle angle on a mnemonic symbol located directly on the case. In modern diodes in a ceramic case, the cathode is usually marked by applying a ring strip near the cathode.

You can check the performance of the thyristor by passing load current through them. To do this, it is allowed to use an incandescent light bulb from old flashlights, the filament of which glows from a current of about 100 mA or less. When current passes through the semiconductor, the light bulb will light up, but if there is no current, it will not.

Read more about how diodes and thyristors work here:

How to check the health of the diode

Usually, to assess the health of the diode, they use an ohmmeter or other devices that have the function of measuring active resistance. By applying voltage to the diode electrodes in the forward and reverse directions, the resistance value is determined. When the p-n junction is open, the ohmmeter will show a value equal to zero, and when closed, it will show infinity.

If there is no ohmmeter, then the health of the diode can be checked using a battery and a light bulb.

Before testing a diode in this way, its power must be taken into account. Otherwise, the load current may destroy the internal structure of the crystal. To evaluate low-power semiconductors, it is recommended to use an LED instead of a light bulb and reduce the load current to 10-15 mA.

How to check the health of a thyristor

The performance of a thyristor can be assessed using several methods. Let's look at three of the most common and available at home.

Battery and light bulb method

When using this method, one should also evaluate the current load of 100 mA created by the light bulb on the internal circuits of the semiconductor and apply it for a short time, especially for the control electrode circuits.

The figure does not show checking that there is no short circuit between the electrodes. This malfunction practically does not occur, but to be completely sure of its absence, you should try passing current through each pair of all three electrodes of the thyristor in the forward and reverse directions. This will only take a few seconds.

When assembling the circuit according to the first option, the semiconductor junction of the device does not pass current, and the light bulb does not light up. This is its main difference in operation from a conventional diode.

To open the thyristor, it is enough to apply a positive source potential to the control electrode. This option is shown in the second diagram. A working device will open its internal circuit and current will flow through it. This will be indicated by the glow of the light bulb filament.

The third diagram shows turning off power from the control electrode and passing current through the anode and cathode. This occurs due to the excess holding current of the internal junction.

The holding effect is used in power control circuits when a short-term current pulse from a phase-shifting device is applied to the control electrode to open the thyristor that controls the amount of alternating current.

The light coming on in the first case or its absence in the second indicates a malfunction of the thyristor. But the loss of glow when the voltage is removed from the control electrode contact can be caused by a current flowing through the anode-cathode circuit that is less than the holding limit value.

An open circuit through the anode or cathode causes the thyristor to turn off.

Test method using a homemade device

The risk of damage to the internal circuits of semiconductor junctions when testing low-power thyristors can be reduced by selecting the current values through each chain. To do this, it is enough to assemble a simple electrical circuit.

The figure shows a device designed to operate from 9-12 volts. When using other supply voltages, the values of resistances R1-R3 should be recalculated.

Rice. 3. Diagram of a device for testing thyristors

A current of about 10 mA is enough to pass through the HL1 LED. If you frequently use the device to connect the electrodes of the VS thyristor, it is advisable to make contact sockets. The SA button allows you to quickly switch the control electrode circuit.

The LED lighting before pressing the SA button or its absence is a clear sign of damage to the thyristor.

Method using tester, multimeter or ohmmeter

The presence of an ohmmeter simplifies the process of checking the thyristor and resembles the previous circuit. In it, the device’s batteries serve as the current source, and instead of the LED glow, the needle deflection for analog models or digital readings on the display for digital devices are used. When the resistance readings are high, the thyristor is closed, and when the resistance is low, it is open.

Here the same three test steps are evaluated with the SA button disabled, pressed for a short time and disabled again. In the third case, the thyristor will most likely change its behavior due to the small value of the current being tested: it will not be enough to hold it.

Low resistance in the first case and high in the second indicate violations of the semiconductor transition.

The ohmmeter method allows you to check the health of semiconductor junctions without unsoldering the thyristor from most circuit boards.

The design of a triac can be conventionally represented as consisting of two thyristors connected opposite to each other. Its anode and cathode do not have strict polarity like a thyristor. They work with alternating electric current.

The quality of the triac state can be assessed using the verification methods described above.