Electrical circuit of car charging for lithium batteries. How to properly charge Li-ion batteries: tips

Charger for li ion batteries, the diagram of which is given in this article, was developed based on the experience of designing similar chargers, efforts to eliminate errors and achieve maximum simplicity. The charger has a highly stable output voltage.

Description of charging for lithium-ion batteries

The main design element is (IO1) - the reference voltage source. Its stability is much better than acceptable, and, as is known for lithium-ion batteries, this is very important characteristic when charging.

Element TL431 is used in this circuit as a current stabilizer in the operation of transistors T1 and T2. Charging current flows through R1. If the voltage drop across this resistor exceeds approximately 0.6 volts, the current flowing through transistors T1 and T2 is limited. The value of resistor R1 is equivalent to the charging current.

The output voltage is controlled by the aforementioned TL431 element. The value is determined by the output voltage divider (R5, R7, P1).

Components R4, C1 for noise suppression. It is very convenient to indicate the amount of charging current using LED1. The glow shows how much current flows in the base circuit of transistor T2, which is proportional to the output current. As the lithium-ion battery charges, the brightness of the LED gradually decreases.

Diode D1 is designed to prevent the lithium-ion battery from discharging when there is no voltage at the input charger. The battery charging circuit does not need protection from incorrect connection polarity of the li-ion battery.

All components are placed on a single-sided printed circuit board.

Current sensor - resistor R1 consists of several resistors connected in parallel. Transistor T2 must be placed on the heat sink. Its size depends on the charging current and the voltage difference between the input and output of the charger.

The circuit of the lithium-ion battery charger is so simple that if the radio components are installed correctly, it should work the first time. The only thing that may be required is to set the output voltage. For a lithium-ion battery, this is approximately 4.2 volts. When idling, transistor T2 should not be hot. The input voltage must be at least 2 volts higher than the required output voltage.

The circuit is designed for charging current up to 1 ampere. If you need to increase the charge current of a li-ion battery, then it is necessary to reduce the resistance of resistor R6 and the output transistor T2 must be of increased power.

At the end of the charging process, the LED still glows a little, to eliminate this, you can simply connect a resistor with a resistance of 10...56 kOhm in parallel with the LED. So, when the charging current drops below 10 mA, the LED will stop lighting.

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It's simple charger for lithium-ion batteries, as well as lithium-polymer batteries are built on the well-known LM317.

The charging process is shown in the graph below. At the first moment of the charging process, the charge current is constant; when the target voltage level (Umax) is reached on the battery, the charger switches to a mode where the voltage remains constant and the current asymptotically tends to zero.

The output voltage of lithium-ion and lithium-polymer batteries is typically 4.2V (4.1V for some types). Usually, the output voltage does not match the nominal voltage which is 3.7V (sometimes 3.6V).

It is not recommended to charge this type batteries to the full 4.2V, as this reduces battery life. If you reduce the output voltage to 4.1V, the capacity drops by 10%, but at the same time the service life (number of cycles) will almost double. When using batteries, the rated voltage cannot be lower than 3.4...3.3V.

Description of the charger

As already mentioned, charging is based on the LM317 stabilizer. Li-Ion and Li-Pol are quite demanding on the accuracy of the charging voltage. If you want to charge to full voltage (usually 4.2V), then you need to set this voltage with an accuracy of plus/minus 1%. After charging to 90% capacity (4.1V), the accuracy may be slightly less (about 3%).

The circuit using LM317 provides fairly accurate voltage stabilization. The target voltage is set by R2. Current stabilization is not as critical as voltage stabilization, so it is enough to stabilize it using a shunt resistor Rx and NPN transistor(VT1).

If the voltage drop across resistor Rx reaches approximately 0.95V, then the transistor begins to open. This reduces the voltage at the “Common” contact of the Lm317 stabilizer and thereby stabilizes the current.

The required charging current for a particular lithium-ion (Li-Ion) and lithium-polymer (Li-Pol) battery is selected by changing the Rx resistance. The resistance Rx approximately corresponds to the following ratio: 0.95/Imax. The Rx resistor value indicated on the diagram corresponds to a current of 200 mA.

The charger's input voltage must be between 9 and 24 volts. Excess this level increases power losses in the LM317 circuit, a decrease will disrupt correct work(you need to recalculate the voltage drop across the shunt and the minimum voltage at the “Common” contact). Transistor VT1 can be replaced with BC237, KC507, C945 or domestic

In modern mobile electronic devices, even those designed to minimize power consumption, the use of non-renewable batteries is becoming a thing of the past. And from an economic point of view - already over a short period of time, the total cost of the required number of disposable batteries will quickly exceed the cost of one battery, and from the point of view of user convenience - it is easier to recharge the battery than to look for where to buy a new battery. Accordingly, battery chargers are becoming a commodity with guaranteed demand. It is not surprising that almost all manufacturers integrated circuits For power supply devices, attention is also paid to the “charging” direction.

Just five years ago, discussion of microcircuits for charging batteries (Battery Chargers IC) began with a comparison of the main types of batteries - nickel and lithium. But at present, nickel batteries have practically ceased to be used and most manufacturers of charge chips have either completely stopped producing chips for nickel batteries or produce chips that are invariant to battery technology (the so-called Multi-Chemistry IC). The STMicroelectronics product range currently includes only microcircuits designed to work with lithium batteries.

Let us briefly recall the main features lithium batteries. Advantages:

• High specific electrical capacity. Typical values ​​are 110...160 W*hour*kg, which is 1.5...2.0 times higher than the same parameter for nickel batteries. Accordingly, with equal dimensions, the capacity of a lithium battery is higher.
• Low self-discharge: approximately 10% per month. In nickel batteries this parameter is 20...30%.

There is no “memory effect”, making this battery easy to maintain: there is no need to discharge the battery to a minimum before recharging.

Disadvantages of lithium batteries:

• The need for current and voltage protection. In particular, it is necessary to exclude the possibility short circuit battery terminals, reverse polarity voltage supply, recharging.
• The need for protection from overheating: heating the battery above a certain level negatively affects its capacity and service life.

There are two industrial technologies for manufacturing lithium batteries: lithium-ion (Li-Ion) and lithium polymer (Li-Pol). However, since the charging algorithms for these batteries are the same, the charging chips do not separate lithium-ion and lithium-polymer technologies. For this reason, we will skip the discussion of the advantages and disadvantages of Li-Ion and Li-Pol batteries, referring to the literature.

Let's consider the algorithm for charging lithium batteries, presented in Figure 1.

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The first phase, the so-called pre-charge, is used only in cases where the battery is very discharged. If the battery voltage is below 2.8 V, then it cannot be immediately charged with the maximum possible current: this will have an extremely negative impact on the battery life. It is necessary to first “recharge” the battery with a low current to approximately 3.0 V, and only after that charging with a maximum current becomes permissible.

Second phase: charger as a constant current source. At this stage, the maximum current for the given conditions flows through the battery. At the same time, the battery voltage gradually increases until it reaches a limit value of 4.2 V. Strictly speaking, upon completion of the second stage, the charge can be stopped, but it should be borne in mind that the battery is at at the moment charged to approximately 70% of its capacity. Note that in many chargers the maximum current is not supplied immediately, but gradually increases to the maximum over several minutes - a “Soft Start” mechanism is used.

If it is desirable to charge the battery to capacity values ​​close to 100%, then we move on to the third phase: the charger as a source of constant voltage. At this stage, a constant voltage of 4.2 V is applied to the battery, and the current flowing through the battery decreases from a maximum to some predetermined minimum value during charging. At the moment when the current value decreases to this limit, the battery charge is considered complete and the process ends.

Let us recall that one of key parameters The battery capacity is its capacity (unit of measurement - A * hour). Thus, the typical capacity of a AAA-size lithium-ion battery is 750…1300 mAh. As a derivative of this parameter, the “current 1C” characteristic is used; this is a current value numerically equal to the rated capacity (in the example given - 750...1300 mA). The value of “current 1C” makes sense only as a determination of the maximum current value when charging the battery and the current value at which the charge is considered complete. It is generally accepted that the maximum current value should not exceed 1*1C, and the battery charge can be considered complete when the current decreases to 0.05...0.10*1C. But these are the parameters that can be considered optimal for a particular type of battery. In reality, the same charger can work with batteries from different manufacturers and of different capacities, while the capacity of a particular battery remains unknown to the charger. Consequently, charging a battery of any capacity will generally not occur in the optimal mode for the battery, but in the mode preset for the charger.

Let's move on to consider the line of charging microcircuits from STMicroelectronics.

Chips STBC08 and STC4054

These microcircuits are fairly simple products for charging lithium batteries. The microcircuits are made in miniature packages such as DFN6 and TSOT23-5L, respectively. This allows these components to be used in mobile devices with fairly stringent requirements for weight and size characteristics (for example, cell phones, MP3 players). Connection schemes STBC08 And STC4054 are presented in Figure 2.

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Despite the limitations imposed by the minimum number of external pins in the packages, the microcircuits have fairly broad functionality:

• There is no need for an external MOSFET, blocking diode or current resistor. As follows from Figure 2, the external wiring is limited by a filter capacitor at the input, a programming resistor and two (for STC4054 - one) indicator LEDs.
• The maximum value of the charge current is programmed by the value of the external resistor and can reach a value of 800 mA. The fact of the end of the charge is determined at the moment when, in constant voltage mode, the value of the charging current drops to a value of 0.1*I BAT, that is, it is also set by the value of the external resistor. The maximum charge current is determined from the relationship:

I BAT = (V PROG /R PROG)*1000;

where I BAT is the charge current in Amperes, R PROG is the resistor resistance in Ohms, V PROG is the voltage at the PROG output, equal to 1.0 Volts.

• In constant voltage mode, a stable voltage of 4.2V is generated at the output with an accuracy of no worse than 1%.
• Charging of heavily discharged batteries automatically begins in pre-charge mode. Until the voltage at the battery output reaches 2.9V, the charge is carried out with a weak current of 0.1*I BAT. This method, as already noted, prevents a very likely failure when trying to charge heavily discharged batteries. in the usual way. In addition, the starting value of the charging current is forcibly limited, which also increases the service life of the batteries.
• An automatic trickle charging mode has been implemented - when the battery voltage drops to 4.05V, the charge cycle will be restarted. This allows you to ensure a constant charge of the battery at a level not lower than 80% of its nominal capacity.
• Protection against overvoltage and overheating. If the input voltage exceeds a certain limit (in particular, 7.2V) or if the case temperature exceeds 120°C, the charger turns off, protecting itself and the battery. Of course, low input voltage protection is also implemented - if the input voltage drops below a certain level (U VLO), the charger will also turn off.
• The ability to connect indication LEDs allows the user to have an idea of ​​the current state of the battery charging process.

Battery charge chips L6924D and L6924U

These microcircuits are devices with greater capabilities compared to STBC08 and STC4054. Figure 3 shows standard schemes switching on microcircuits L6924D And L6924U .

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Let's consider those functional features L6924 chips, which relate to setting the parameters of the battery charging process:

1. In both modifications it is possible to set the maximum duration of battery charge starting from the moment of switching to DC stabilization mode (the term “mode” is also used fast charging" - Fast charge phase). When entering this mode, a watchdog timer is started, programmed for a certain duration T PRG by the value of the capacitor connected to the T PRG pin. If before operation of this timer If the battery charge is not stopped according to the standard algorithm (the current flowing through the battery decreases below the I END value), then after the timer is triggered, charging will be interrupted forcibly. Using the same capacitor, the maximum duration of the pre-charging mode is set: it is equal to 1/8 of the duration T PRG. Also, if during this time there is no transition to fast charging mode, the circuit turns off.

2. Pre-charge mode. If for the STBC08 device the current in this mode was set as a value equal to 10% of I BAT, and the switching voltage to DC mode was fixed, then in the L6924U modification this algorithm was preserved unchanged, but in the L6924D chip both of these parameters are set using external resistors connected to inputs I PRE and V PRE.

3. The sign of completion of charging in the third phase (DC voltage stabilization mode) in STBC08 and STC4054 devices was set as a value equal to 10% of I BAT. In L6924 microcircuits, this parameter is programmed by the value of an external resistor connected to the I END pin. In addition, for the L6924D chip, it is possible to reduce the voltage at the V OUT pin from the generally accepted value of 4.2 V to 4.1 V.

4. The value of the maximum charging current I PRG in these microcircuits is set in the traditional way - through the value of an external resistor.

As you can see, in simple “charging” STBC08 and STC4054, only one parameter was set using an external resistor - the charging current. All other parameters were either rigidly fixed or were a function of I BAT. The L6924 chips have the ability to fine-tune several more parameters and, in addition, provide “insurance” for the maximum duration of the battery charging process.

For both modifications of the L6924, two operating modes are provided if the input voltage is generated by the AC/DC network adapter. First - standard mode linear step-down regulator of output voltage. The second is the quasi-pulse regulator mode. In the first case, a current can be supplied to the load, the value of which is slightly less than the value of the input current taken from the adapter. In the DC stabilization mode (second phase - Fast charge phase), the difference between the input voltage and the voltage at the “plus” of the battery is dissipated as thermal energy, as a result of which the dissipated power in this charge phase is maximum. When operating in switching regulator mode, a current whose value is higher than the value of the input current can be supplied to the load. In this case, significantly less energy is lost into heat. This, firstly, reduces the temperature inside the case, and secondly, increases the efficiency of the device. But it should be borne in mind that the accuracy of current stabilization in linear mode equals approximately 1%, and in pulsed mode - about 7%.

The operation of L6924 microcircuits in linear and quasi-pulse modes is illustrated in Figure 4.

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The L6924U chip, in addition, may not work from network adapter, but from the USB port. In this case, the L6924U chip implements some technical solutions, which can further reduce power dissipation by increasing charging time.

The L6924D and L6924U chips have an additional input for forced charge interruption (that is, load shutdown) SHDN.

In simple charging microcircuits, temperature protection consists of stopping the charge when the temperature inside the microcircuit case rises to 120°C. This, of course, is better than no protection at all, but the value of 120°C on the case is more than conditionally related to the temperature of the battery itself. The L6924 products provide the ability to connect a thermistor directly related to the battery temperature (resistor RT1 in Figure 3). In this case, it becomes possible to set the temperature range in which charging the battery will be possible. On the one side, lithium batteries It is not recommended to charge at sub-zero temperatures, and on the other hand, it is also extremely undesirable if the battery heats up to more than 50°C during charging. The use of a thermistor makes it possible to charge the battery only under favorable temperature conditions.

Naturally, additional functionality The L6924D and L6924U microcircuits not only expand the capabilities of the designed device, but also lead to an increase in the area on the board, occupied both by the microcircuit body itself and by external trim elements.

Battery charging chips STBC21 and STw4102

This is a further improvement of the L6924 chip. On the one hand, approximately the same functional package is implemented:

• Linear and quasi-pulse mode.
• Thermistor connected to battery like key element temperature protection.
• Ability to set quantitative parameters for all three phases of the charging process.

Some additional features, missing in L6924:

• Reverse polarity protection.
• Short circuit protection.
• A significant difference from the L6924 is the presence digital interface I 2 C to set parameter values ​​and other settings. As a result, more precise settings of the charging process become possible. Recommended connection diagram STBC21 is shown in Figure 5. It is obvious that in in this case There is no question about saving board area and strict weight and size characteristics. But it is also obvious that the use of this microcircuit in small-sized voice recorders, players and mobile phones simple models not expected. Rather, these are batteries for laptops and similar devices, where replacing the battery is an infrequent procedure, but also not cheap.

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5. Camiolo Jean, Scuderi Giuseppe. Reducing the Total No-Load Power Consumption of Battery Chargers and Adapter Applications Polymer // Material from STMicroelectronics. Online posting:

The charging and discharging processes of any battery occur in the form of a chemical reaction. However, charging lithium-ion batteries is an exception to the rule. Scientific research show the energy of such batteries as the chaotic movement of ions. The statements of pundits deserve attention. If according to science you charge correctly lithium ion batteries, then these devices should last forever.

Scientists see evidence of loss of useful battery capacity, confirmed by practice, in ions blocked by so-called traps.

Therefore, as is the case with other similar systems, lithium-ion devices are not immune to defects during their use in practice.

Chargers for Li-ion designs have some similarities with devices designed for lead-acid systems.

But the main differences between such chargers are seen in the supply of increased voltages to the cells. In addition, there are tighter current tolerances, plus the elimination of intermittent or floating charging when the battery is fully charged.

If there is some flexibility in terms of connecting/disconnecting voltage, manufacturers of lithium-ion systems categorically reject this approach.

Li-ion batteries and the operating rules for these devices do not allow for the possibility of unlimited overcharging.

Therefore, there is no so-called “miracle” charger for lithium-ion batteries that can extend their service life for a long time.

It is impossible to obtain additional Li-ion capacity through pulse charging or other known tricks. Lithium-ion energy is a kind of “clean” system that accepts a strictly limited amount of energy.

Charging cobalt-blended batteries

Classic designs lithium ion batteries equipped with cathodes whose structure is made up of materials:

• cobalt,
• nickel,
• manganese,
• aluminum.

All of them are usually charged at a voltage of up to 4.20V/I. The permissible deviation is no more than +/- 50 mV/I. But there are also certain types of nickel-based lithium-ion batteries that allow a charge voltage of up to 4.10V/I.

There are also developments of lithium-ion batteries, where the percentage of lithium has been increased. For them, the charge voltage can reach 4.30V/I and higher.

Well, increasing the voltage increases the capacity, but if the voltage goes beyond the specification, it can lead to destruction of the battery structure.

Therefore, for the most part, lithium-ion batteries are equipped with protective circuits, the purpose of which is to maintain the established standard.

Full or partial charge

However, practice shows: most powerful lithium-ion batteries can take more high level voltage provided that it is supplied for a short time.

With this option, the charging efficiency is about 99%, and the cell remains cool during the entire charging time. True, some lithium-ion batteries still heat up by 4-5C when fully charged.

This may be due to protection or due to high internal resistance. For such batteries, the charge should be stopped when the temperature rises above 10ºC at a moderate charge rate.

Full charging of cobalt-blended systems occurs at a threshold voltage. In this case, the current drops by up to 3-5% of the nominal value.

The battery will show a full charge even when it reaches a certain capacity level that remains unchanged for a long time. The reason for this may be increased self-discharge of the battery.

Increasing charge current and charge saturation

It should be noted that increasing the charge current does not speed up the achievement of a full charge state. Lithium will reach peak voltage faster, but charging until the capacity is completely saturated takes longer. However, charging the battery at high current quickly increases the battery capacity to approximately 70%.

Lithium-ion batteries do not require a full charge, as is the case with lead-acid devices. Moreover, this charging option is undesirable for Li-ion. In fact, it is better to not fully charge the battery, because high voltage“strains” the battery.

Choice of threshold more low voltage or complete removal of the saturation charge help extend the life of the lithium-ion battery. True, this approach is accompanied by a decrease in the battery energy release time.

It's worth noting here: household chargers typically run on maximum power and do not support charging current (voltage) adjustment.

Manufacturers of consumer lithium-ion battery chargers consider long battery life to be less important than the cost of circuit complexity.

Li-ion battery chargers

Some cheap household chargers often work using a simplified method. Charge a lithium-ion battery in one hour or less, without going to saturation charge.

The ready indicator on such devices lights up when the battery reaches the voltage threshold in the first stage. The state of charge is about 85%, which often satisfies many users.

Professional chargers (expensive) are distinguished by the fact that they set the charging voltage threshold lower, thereby extending the life of the lithium-ion battery.

The table shows the calculated power when charging with such devices at different voltage thresholds, with and without saturation charge:

As soon as the lithium-ion battery begins to charge, there is a rapid increase in voltage. This behavior is comparable to lifting a load with a rubber band when there is a lag effect.

Capacity will eventually be gained when the battery is fully charged. This charge characteristic is typical for all batteries.

The higher the charge current, the brighter the effect rubber band. Low temperature or the presence of a cell with high internal resistance only enhances the effect.

Assessing the state of charge by reading the voltage of a charged battery is impractical. Measuring the open circuit (idle) voltage after the battery has been sitting for several hours is the best evaluation indicator.

As with other batteries, temperature affects idle speed in the same way it affects the active material of a lithium-ion battery. , laptops and other devices is estimated by counting coulombs.

Lithium-ion battery: saturation threshold

A lithium-ion battery cannot absorb excess charge. Therefore, when the battery is completely saturated, the charging current must be removed immediately.

A constant current charge can lead to metallization of lithium elements, which violates the principle of ensuring the safe operation of such batteries.

To minimize the formation of defects, you should disconnect the lithium-ion battery as quickly as possible when it reaches peak charge.

As soon as the charge stops, the voltage of the lithium-ion battery begins to drop. The effect of reducing physical stress appears.

Tension for a while idle speed will be distributed between unevenly charged cells with a voltage of 3.70 V and 3.90 V.

Here, the process also attracts attention when a lithium-ion battery, which has received a fully saturated charge, begins to charge the neighboring one (if one is included in the circuit), which has not received a saturation charge.

When lithium-ion batteries need to be constantly kept on the charger in order to ensure their readiness, you should rely on chargers that have a short-term compensation charge function.

The flash charger turns on when the open circuit voltage drops to 4.05 V/I and turns off when the voltage reaches 4.20 V/I.

Chargers designed for hot-ready or standby operation often allow battery voltages as low as 4.00V/I and will only charge Li-Ion batteries to 4.05V/I rather than reaching the full 4.20V/I level.

This technique reduces physical voltage, which is inherently associated with technical voltage, and helps extend battery life.

Charging cobalt-free batteries

Traditional batteries have a nominal cell voltage of 3.60 volts. However, for devices that do not contain cobalt, the rating is different.

Thus, lithium phosphate batteries have a nominal value of 3.20 volts (charging voltage 3.65V). And new lithium titanate batteries (made in Russia) have a nominal cell voltage of 2.40V (charger voltage 2.85).

Traditional chargers are not suitable for such batteries, as they overload the battery with the risk of explosion. Conversely, a charging system for cobalt-free batteries will not provide sufficient charge to a traditional 3.60V lithium-ion battery.

Exceeded charge of lithium-ion battery

The lithium-ion battery operates safely within specified operating voltages. However, battery performance becomes unstable if it is charged above operating limits.

Long-term charging of a lithium-ion battery with a voltage above 4.30V, designed for an operating rating of 4.20V, is fraught with lithium metalization of the anode.

The cathode material, in turn, acquires the properties of an oxidizing agent, loses its stability, and releases carbon dioxide.

The pressure of the battery cell increases and if charging continues, the internal protection device will operate at a pressure between 1000 kPa and 3180 kPa.

If the pressure rise continues after this, the protective membrane opens at a pressure level of 3.450 kPa. In this state, the lithium-ion battery cell is on the verge of exploding and eventually does just that.

Triggering of the protection inside a lithium-ion battery is associated with an increase in the temperature of the internal contents. Fully charged battery has a higher internal temperature than a partially charged one.

Therefore, lithium-ion batteries appear to be safer when charged at a low level. That is why the authorities of some countries require the use of Li-ion batteries in aircraft that are saturated with energy no more than 30% of their full capacity.

Battery internal temperature threshold at fully loaded is:

• 130-150°C (for lithium-cobalt);
• 170-180°C (for nickel-manganese-cobalt);
• 230-250°C (for lithium manganese).

It should be noted: lithium phosphate batteries have better temperature stability than lithium manganese batteries. Lithium-ion batteries are not the only ones that pose a danger in energy overload conditions.

For example, lead-nickel batteries are also prone to melting with subsequent fire if energy saturation is carried out in violation of the passport regime.

Therefore, using chargers that are perfectly matched to the battery is of paramount importance for all lithium-ion batteries.

Some conclusions from the analysis

Charging lithium-ion batteries has a simplified procedure compared to nickel systems. The charging circuit is straightforward, with voltage and current limits.

This circuit is much simpler than a circuit that analyzes complex voltage signatures that change as the battery is used.

The energy saturation process of lithium-ion batteries allows for interruptions; these batteries do not need to be fully saturated, as is the case with lead-acid batteries.

The properties of lithium-ion batteries promise benefits in the operation of renewable energy sources ( solar panels and wind turbines). As a rule, a wind generator rarely provides a full battery charge.

For lithium-ion, the lack of steady-state charging requirements simplifies the charge controller design. A lithium-ion battery does not require a controller to equalize voltage and current, as is required by lead-acid batteries.

All household and most industrial lithium-ion chargers fully charge the battery. However existing devices Charging lithium-ion batteries generally do not provide voltage regulation at the end of the cycle.

Lithium-ion batteries are very popular these days and are used in various gadgets, for example phones, smart watch, players, flashlights, laptops. For the first time, a battery of this type (Li-ion) was produced by the famous Japanese company Sony. Schematic diagram The simplest battery is shown in the picture below; by assembling it, you will have the opportunity to restore the charge in the batteries yourself.

Homemade lithium battery charging - electrical diagram

The basis for this device are two stabilizer microcircuits 317 and 431 (). In this case, the LM317 integrated stabilizer serves as a current source; we take this part in the TO-220 housing and must install it on the heat sink using thermal paste. The TL431 voltage regulator manufactured by Texas Instruments also exists in SOT-89, TO-92, SOP-8, SOT-23, SOT-25 and other packages.

Light emitting diodes (LED) D1 and D2 of any color you like. I chose the following: LED1 red rectangular 2.5 mm (2.5 milCandelas) and LED2 green diffusion 3 mm (40-80 milCandelas). Convenient to use smd leds if you don't install ready-made board into the body.

The minimum power of resistor R2 (22 Ohm) is 2 Watts, and R5 (11 Ohm) is 1 Watt. All other ones are 0.125-0.25W.

The 22 kiloOhm variable resistor must be of type SP5-2 (imported 3296W). Such variable resistors have very precise resistance adjustment, which can be smoothly adjusted by twisting a worm pair similar to a bronze bolt.

Photo of measuring the voltage of a li-ion battery from cell phone before charging (3.7V) and after (4.2V), capacity 1100 mA*h.

PCB for lithium charger

Printed circuit board (PCB) comes in two formats for different programs- the archive is located. Finished sizes printed circuit board in my case, 5 by 2.5 cm. I left space on the sides for fastenings.

How does charging work?

How does the finished circuit of such a charger work? The battery is charged first direct current, which is determined by the resistance of resistor R5, with a standard rating of 11 Ohms it will be approximately 100 mA. Next, when the rechargeable energy source has a voltage of 4.15-4.2 volts, charging will begin constant voltage. When the charging current drops to low values, LED D1 will stop lighting.

As is known, the standard voltage for Li-ion charging is 4.2V, this figure It is necessary to install the circuit at the output without load, using a voltmeter, so the battery will be fully charged. If you reduce the voltage a little, by about 0.05-0.10 Volts, then your battery will not be fully charged, but this way it will last longer. Author of the article EGOR.

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