How to increase the computer's power supply voltage. Converting an ATX computer power supply into an adjustable power supply

Overclocking the power supply.

The author is not responsible for the failure of any components resulting from overclocking. Using these materials for any purpose, end user accepts all responsibility. The site materials are presented "as is"."

Introduction.

I started this experiment with frequency due to the lack of power in the power supply.

When the computer was purchased, its power was quite sufficient for this configuration:

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For example, two diagrams:

Frequency f for this circuit it turned out to be 57 kHz.

And for this frequency f equal to 40 kHz.

Practice.

The frequency can be changed by replacing the capacitor C or/and resistor R to a different denomination.

It would be correct to install a capacitor with a smaller capacitance, and replace the resistor with a series-connected constant resistor and type variable SP5 with flexible leads.

Then, decreasing its resistance, measure the voltage until the voltage reaches 5.0 volts. Then solder a constant resistor in place of the variable one, rounding the value up.

I took a more dangerous path - I sharply changed the frequency by soldering in a capacitor of smaller capacity.

I had:

R 1 =12kOm
C 1 =1.5nF

According to the formula we get

f=61.1 kHz

After replacing the capacitor

R 2 =12kOm
C 2 =1.0nF

f =91.6 kHz

According to the formula:

the frequency increased by 50% and the power increased accordingly.

If we do not change R, then the formula simplifies:

Or if we don’t change C, then the formula is:

Trace the capacitor and resistor connected to pins 5 and 6 of the microcircuit. and replace the capacitor with a capacitor with a smaller capacity.

Result

After overclocking the power supply, the voltage became exactly 5.00 (the multimeter can sometimes show 5.01, which is most likely an error), almost without reacting to the tasks being performed - with a heavy load on the +12 volt bus (simultaneous operation of two CDs and two screws) - the voltage on the + bus 5V may drop briefly to 4.98.

The key transistors began to heat up more. Those. If before the radiator was slightly warm, now it is very warm, but not hot. The radiator with rectifier half-bridges did not heat up any more. The transformer also does not heat up. From 09/18/2004 to this day (01/15/05) there are no questions about the power supply. On at the moment following configuration:

Links

1. PARAMETERS OF THE MOST COMMON POWER TRANSISTORS USED IN PUSH-CYCLE UPS CIRCUITS MANUFACTURED FOREIGN.
2. Capacitors. (Note: C = 0.77 ۰ Nom ۰SQRT(0.001۰f), where Nom is the rated capacitance of the capacitor.)

Rennie's comments: The fact that you increased the frequency, you increased the number of sawtooth pulses over a certain period of time, and as a result, the frequency with which power instabilities are monitored increased, since power instabilities are monitored more often, the pulses for closing and opening of transistors in a half-bridge switch occur at double frequency . Your transistors have characteristics, specifically their speed: By increasing the frequency, you have thereby reduced the size of the dead zone. Since you say that the transistors do not heat up, it means they are in that frequency range, which means everything seems to be fine here. But there is also pitfalls. Do you have an electrical circuit diagram in front of you? I’ll explain it to you now using the diagram. There in the circuit, look where the key transistors are, diodes are connected to the collector and emitter. They serve to dissolve the residual charge in the transistors and transfer the charge to the other arm (to the capacitor). Now, if these comrades have a low switching speed, through currents are possible - this is a direct breakdown of your transistors. Perhaps this will cause them to heat up. Now further, this is not the case, the point is that after the direct current that passed through the diode. It has inertia and when a reverse current appears: for some time the value of its resistance is not restored and therefore they are characterized not by the frequency of operation, but by the recovery time of the parameters. If this time is longer than possible, then you will experience partial through currents, which is why surges in both voltage and current are possible. In the secondary it’s not so scary, but in the power department it’s just fucked up: to put it mildly. So let's continue. In the secondary circuit, these switchings are not desirable, namely: There, Schottky diodes are used for stabilization, so at 12 volts they are supported with a voltage of -5 volts (approx. I have silicon ones at 12 volts), so at 12 volts that If only they (Schottky diodes) could be used with a voltage of -5 volts. (Due to low reverse voltage, it is impossible to simply install Schottky diodes on a 12 volt bus, that’s why they are distorted in this way). But silicon diodes have more losses than Schottky diodes and the reaction is less, unless they are one of the fast-recovery diodes. So, if high frequency, then Schottky diodes have almost the same effect as in the power section + the inertia of the winding at -5 volts relative to +12 volts makes it impossible to use Schottky diodes, so an increase in frequency can eventually lead to failure of the diodes. I'm considering the general case. So let's move on. Next is another joke, finally connected directly with the chain feedback. When you create negative feedback, you have such a thing as the resonant frequency of this feedback loop. If you reach resonance, then your whole scheme will be screwed. Sorry for the rude expression. Because this PWM chip controls everything and requires its operation in mode. And at the end" dark horse" ;) Do you understand what I mean? It’s the transformer, and this piece of shit also has a resonant frequency. So this crap is not a unified part, the transformer and winding product are manufactured individually in each case - for this simple reason you don’t know the characteristics of him. And if you introduce your frequency into resonance? You will burn out your trance and you can safely throw away two absolutely identical transformers. Well, the fact is that by choosing the wrong frequency you could easily burn out the power supply. Under all other conditions. How to increase the power of the power supply? First of all, we need to understand what power is. The voltage in the power part is 310 volts constant. influence. We have only one trans. We can only increase the current. The amount of current is dictated to us by two things - the transistors in the half-bridge and the buffer capacitors are larger, the transistors are more powerful, so we need to increase the capacitance rating and change the transistors to those with such ones. more current in the collector-emitter circuit or just collector current, if you don’t mind, you can plug in 1000 uF there and not bother with calculations. So in this circuit we did everything we could, here, in principle, nothing more can be done, except perhaps taking into account the voltage and current of the base of these new transistors. If the transformer is small, this will not help. You also need to regulate such crap as the voltage and current at which your transistors will open and close. Now it seems like everything is here. Let's go to the secondary circuit. Now we have a lot of current at the output windings....... We need to slightly correct our filtering, stabilization and rectification circuits. For this, we take, depending on the implementation of our power supply, and change the diode assemblies first of all, so that we can ensure the flow of our current. In principle, everything else can be left as is. That's all, it seems, well, at the moment there should be a margin of safety. The point here is that the technique is impulsive - this is its bad side. Here almost everything is built on the frequency response and phase response, on t reaction.: that’s all

How to make a full-fledged power supply yourself with an adjustable voltage range of 2.5-24 volts is very simple; anyone can repeat it without any amateur radio experience.

We'll make it out of old computer unit power supply, TX or ATX, it doesn’t matter, fortunately, over the years of the PC Era, every home has already accumulated quite a lot of old computer hardware and the power supply is probably there too, so the cost of the homemade product will be insignificant, and for some craftsmen it will be zero rubles.

I got this AT block for modification.

Look what is written on the case.

There are many options for modifying a standard computer power supply, but they are all based on a change in the wiring of the IC chip - TL494CN (its analogues DBL494, KA7500, IR3M02, A494, MV3759, M1114EU, MPC494C, etc.).

Let's look at several options execution of computer power supply circuits, perhaps one of them will be yours and dealing with the wiring will become much easier.

Scheme No. 1.

Let's get to work.
First you need to disassemble the power supply housing, unscrew the four bolts, remove the cover and look inside.

In my case, a KA7500 chip was found on the board, which means we can begin to study the wiring and the location of unnecessary parts that need to be removed.

Let's disconnect the power and fan, solder or cut out the output wires so that they don't interfere with our understanding of the circuit, leave only the necessary ones, one yellow (+12v), black (common) and green* (start ON) if there is one.

This is done because our modified unit will produce not +12 volts, but up to +24 volts, and without replacement, the capacitors will simply explode during the first test at 24v, after a few minutes of operation. When selecting a new electrolyte, it is not advisable to reduce the capacity; increasing it is always recommended.

The most important part of the job.
We will remove all unnecessary parts in the IC494 harness and solder other nominal parts so that the result is a harness like this (Fig. No. 1).

We will only need these legs of the microcircuit No. 1, 2, 3, 4, 15 and 16, do not pay attention to the rest.

Explanation of symbols.

Some resistors that are already soldered into the wiring diagram can be suitable without replacing them, for example, we need to put a resistor at R=2.7k connected to the “common”, but there is already R=3k connected to the “common”, this suits us quite well and we leave it there unchanged (example in Fig. No. 2, green resistors do not change).

Thus, we review and redo all the circuits on the six legs of the microcircuit.

This was the most difficult point in the rework.

We make voltage and current regulators.

Voltage and current control.
To control we need a voltmeter (0-30v) and an ammeter (0-6A).

IMPORTANT- inside the device there is a Current resistor (Current sensor), which we need according to the diagram (Fig. No. 1), therefore, if you use an ammeter, then you do not need to install an additional Current resistor; you need to install it without an ammeter. Usually a homemade RC is made, a wire D = 0.5-0.6 mm is wound around a 2-watt MLT resistance, turn to turn for the entire length, solder the ends to the resistance terminals, that's all.

Everyone will make the body of the device for themselves.
You can leave it completely metal by cutting holes for regulators and control devices. I used laminate scraps, they are easier to drill and cut.

Instructions

Regardless of which power supply you want to increase the output voltage, first make sure that the load will not be damaged.

Do not try to increase the output voltage of switching power supplies, especially those with a feedback optocoupler. Impulse ones are calculated with almost no reserve. By forcing such a transformer to produce on the winding increased voltage, you can cause it to break down.

In some power supplies, the ability to adjust is provided initially. It can be smooth or stepped. In the first case, turn the knob clockwise until the desired voltage is achieved, in the second, move the switch to the desired position. If the power supply is unstabilized, to increase the voltage at its output, simply reduce the load current. Beware of breakdown of the filter capacitors if they are not designed for voltage. If necessary, replace them with others rated for voltage.

For a power supply with a stabilizer on the LM317(T) chip, to increase the output voltage, increase the value connected between the common wire and the control terminal and proportionally reduce the value of the resistor connected between and the control terminal.

For a stabilizer on a 78xx chip, connect a zener diode between the common wire and the common terminal (cathode to general conclusion microcircuits). The output voltage will increase by the stabilization voltage of this.

In a parametric stabilizer, to increase the voltage, replace the zener diode with another one with a higher stabilization voltage.

To increase the voltage at the output of an unstabilized power supply, replace the bridge rectifier in it with a voltage doubler.

If the voltage at the output of the power supply needs to be increased without any alteration, place a converter of any suitable design after it.

Has your favorite computer stopped turning on? Identify the causes of the problem by testing your PC. Learn the basics of diagnosing when technology problems become intermittent. You yourself can detect damaged equipment elements.

You will need

• -motherboard;
• -multimeter;
• -accuracy.

Instructions

Before starting repairs, find out if the equipment is not working. The failure may be software or related to the computer hardware. Using measuring instruments, determine the parameters of the equipment. Measure the voltage with a voltmeter, check the elements printed circuit boards oscilloscope, check hard programs disk.

DC voltage used in computers has standard values. For PC nodes, voltage is supplied by a power supply installed in the system unit. Measure the readings given. The obtained values ​​should not deviate from the standard by more than 5%. Disconnect the computer from power. Unscrew the screws and remove the cover system unit. Measure the voltage on the motherboard. To do this, take the switch and set it to constant voltage. The DC voltage icon will look like this: V; or so: DCV. Turn the handle to 20, since the voltage is low.

Next, connect two different colored probes to the tester. The black probe is called common, minus or ground, connect it to the COM connector. Connect the red probe to the connector located just above the first one. In order to measure the voltage of the motherboard, connect the black probe to the black contact on the connector branching from the power supply. Touch the red probe to the motherboard. Knowing the voltage of the corresponding point, you can easily understand the cause of the breakdown. Study the diagram that comes with motherboard. You will learn what voltages should be at each point. Voltage can be measured without reaching motherboard from the body. To do this, use a crocodile clip that clings to the body itself. Make sure there is no paint in this area because it will act as an insulator.

Please note

There are many subtleties in this matter; skill comes with practice.

Useful advice

Do not leave the multimeter turned on in ohmmeter mode - the battery charge will quickly be lost.

Sometimes the load is designed to be supplied with a voltage lower than that produced by the existing source. In addition, some loads, when powered by reduced voltage, operate in a lighter mode and last longer. The method of reducing the voltage on the powered device depends on its type and parameters.

Instructions

Before lowering the load supply voltage, make sure that the reduction will actually benefit it. For example, in a halogen lamp, a decrease in voltage can stop the tungsten exchange cycle between the filament and the gas, and it will burn out even faster; an electric motor with too low voltage can stop, begin to consume increased current and burn out, and a switching power supply or energy saving lamp- start working in an unfavorable mode and fail very quickly.

The simplest, almost universal method on the load - connecting a resistor in series with it. Select a resistor that can withstand the power generated by it. In this case, the efficiency will decrease slightly. If you are absolutely sure that the load is active, use a reactance element - a suitable capacitor or inductor. For safety, bridge the capacitor with a megaohm resistor. If you have two identical active loads, connect them in series.

For downgrading (and upgrading) AC voltage Autotransformers have been used for about a century. Unlike transformers, they do not provide galvanic isolation, but have significantly smaller dimensions for the same power. Laboratory autotransformers (LATRs) are especially convenient, allowing smooth regulation of the output voltage. Select the correct autotransformer for power, and under no circumstances use it on DC.

To reduce low DC voltage while stabilizing it, use a parametric or compensation stabilizer. The second one is more complicated, but more effective. A switching stabilizer has an even higher efficiency, but it can interfere with a load that contains circuits that are sensitive to them.

Convert high voltage low voltage with simultaneous galvanic isolation from the network is possible with power supplies of various designs. Such blocks - internal or external - are widely used as part of modern electronic equipment. Many of them are equipped with built-in stabilizers. Select the right unit depending on the load parameters (voltage, current, sensitivity to interference).

Video on the topic

Please note

Do not work under voltage or allow short circuits, even if galvanic isolation and protection are provided. Having become accustomed to a safe, low-voltage power supply with isolation and protection, the next time the user may forget to follow safety precautions when working with a dangerous power source.

The converter is made on transistor VT1 and transformer T1. Mains voltage across surge protector(SF) is supplied to the network rectifier (SV), where it is rectified, filtered by the filter capacitor Sf and through the winding W1 of transformer T1 is supplied to the collector of transistor VT1. When a transistor is fed into the base circuit rectangular pulse, the transistor opens and an increasing current Ik flows through it. The same current will flow through the winding W1 of transformer T1, which will lead to an increase in the magnetic flux in the transformer core, while a self-induction emf is induced in the secondary winding W2 of the transformer. Ultimately, a positive voltage will appear at the output of the diode VD. Moreover, if we increase the duration of the pulse applied to the base of transistor VT1, the voltage in the secondary circuit will increase, because more energy will be released, and if we decrease the duration, the voltage will decrease accordingly. Thus, by changing the pulse duration in the base circuit of the transistor, we can change the output voltages of the secondary winding T1, and therefore stabilize the output voltages of the power supply.
The only thing that is needed for this is a circuit that will generate trigger pulses and control their duration (latitude). A PWM controller is used as such a circuit. PWM is pulse width modulation. The PWM controller includes a master pulse generator (which determines the operating frequency of the converter), protection, control and logic circuit, which controls the pulse duration.
To stabilize the output voltages of the UPS, the PWM controller circuit “must know” the magnitude of the output voltages. For these purposes, a tracking circuit (or feedback circuit) is used, made on optocoupler U1 and resistor R2. An increase in voltage in the secondary circuit of transformer T1 will lead to an increase in the intensity of the LED radiation, and therefore a decrease in the junction resistance of the phototransistor (part of the optocoupler U1). Which in turn will lead to an increase in the voltage drop across resistor R2, which is connected in series with the phototransistor and a decrease in the voltage at pin 1 of the PWM controller. A decrease in voltage causes the logic circuit included in the PWM controller to increase the pulse duration until the voltage at the 1st pin matches given parameters. When the voltage decreases, the process is reversed.
The UPS uses 2 principles for implementing tracking circuits - “direct” and “indirect”. The method described above is called “direct”, since the feedback voltage is removed directly from the secondary rectifier. With “indirect” tracking, the feedback voltage is removed from the additional winding of the pulse transformer:

A decrease or increase in the voltage on winding W2 will lead to a change in voltage on winding W3, which is also applied through resistor R2 to pin 1 of the PWM controller.
I think we've sorted out the tracking chain, now let's consider the following situation: short circuit(KZ) in UPS load. In this case, all the energy supplied to the secondary circuit of the UPS will be lost and the output voltage will be almost zero. Accordingly, the PWM controller circuit will try to increase the pulse duration in order to raise the level of this voltage to the appropriate value. As a result, transistor VT1 will remain open longer and longer, and the current flowing through it will increase. Ultimately, this will lead to the failure of this transistor. The UPS provides protection for the converter transistor against current overloads in such emergency situations. It is based on a resistor Rprotect, connected in series to the circuit through which the collector current Ik flows. An increase in the current Ik flowing through transistor VT1 will lead to an increase in the voltage drop across this resistor, and, consequently, the voltage supplied to pin 2 of the PWM controller will also decrease. When this voltage drops to a certain level, which corresponds to the maximum permissible current of the transistor, the logic circuit of the PWM controller will stop generating pulses at pin 3 and the power supply will go into protection mode or, in other words, turn off.
In conclusion of the topic, I would like to describe in more detail the advantages of the UPS. As already mentioned, the frequency of the pulse converter is quite high, and therefore, overall dimensions pulse transformer are reduced, which means, as paradoxical as it sounds, the cost of a UPS is less than a traditional power supply, since there is less metal consumption for the magnetic core and copper for the windings, even though the number of parts in the UPS increases. Another advantage of the UPS is the small capacitance of the secondary rectifier filter capacitor compared to a conventional power supply. Reducing the capacitance was made possible by increasing the frequency. And finally, efficiency pulse block nutrition reaches 85%. This is due to the fact that the UPS consumes energy electrical network only when the converter transistor is open, when it is closed, energy is transferred to the load due to the discharge of the secondary circuit filter capacitor.
The disadvantages include the complication of the UPS circuit and the increase in pulse noise emitted by the UPS itself. The increase in interference is due to the fact that the converter transistor operates in switch mode. In this mode, the transistor is a source of impulse noise that occurs at moments transient processes transistor. This is a disadvantage of any transistor operating in switching mode. But if the transistor operates with low voltages (for example, transistor logic with a voltage of 5 volts), this is not a problem; in our case, the voltage applied to the collector of the transistor is approximately 315 volts. To combat this interference, UPSs use more complex circuits network filters than in a conventional power supply.

But there is still a way out. This is an ordinary, standard ATX from any, even the simplest and most ancient computer. Despite the cheapness of such power supplies (second-hand ones can be found from companies and for 5e), they provide very decent current and universal voltages. On the +12V line - 10A, on the -12V line - 1A, on the 5V line - 12A and on the 3.3V line - 15A. Of course, these values ​​are not exact and may vary slightly depending on specific model ATX PSU.

Just recently I did one interesting thing - a music center made from the housing of a small speaker. Everything would be fine, but given the decent power of the bass amplifier, the current consumption of the center in the bass peaks reached 8A. And even an attempt to install a 100-watt transformer with 4-amp secondary power supply did not give a normal result: not only did the voltage drop by 3-4 volts in the bass (which was clearly visible from the attenuation of the backlight lamps on the front panel of the radio), but also There was no way to get rid of the 50Hz background. At least set it to 20,000 microfarads, or at least shield everything you can.

And just as luck would have it, the old system unit burned out at work. But the block ATX power supply still working. So we'll plug it in for the radio. Although according to the passport, car radios and their amplifiers are powered by a voltage of 12V, we know that it will sound much more powerful if 15-17V is applied to it. At least in my entire history, not a single receiver has ever burned out from an extra 5 volts.

Since in the existing ATX power supply the voltage of the 12-volt bus was only a little more than 10V (maybe that’s why the system unit didn’t work? It’s too late), we will raise it by changing the control voltage on the 2nd pin of the TL494. Schematic diagram computer power supply, see here.

Simply put, we’ll change the resistor or even solder it onto tracks of a different value. I set two kilo-ohms and 10.5V turns into 17. Do you need less? - We increase the resistance. The computer power supply starts by shorting the green wire to any black wire.

Since there is not a lot of space in the case of the future music center, we take out the ATX switching power supply board from the original case (the box will be useful for my future project), and thereby reduce the dimensions of the power supply by half. And don’t forget to resolder the filter capacitor in the power supply to a higher voltage, otherwise you never know...

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