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Simple and reliable lithium battery charging scheme (circuit diagram)

by:dcfpower     2021-03-18
u003cpu003eu003c/pu003eu003cpu003eA: The circuit characteristics of Figure 1 are relatively simple, easy to understand, easy to obtain components, complete functions, and ideal characteristics. Vin is DC, and distillation voltage is sufficient, but the minimum input needs to be 2V higher than vout. Figure 2 is an improved version. In terms of function, it can charge 1 to 4 lithium batteries (converted through R2), and the charging current is continuously adjustable from 0.1 to 3A (through R5). The method is high-precision constant current and constant voltage (CC/ CV). In terms of indication, white, red, orange, and green LEDs are used to indicate power, fast charge, slow charge, full charge, short-circuit protection, over-voltage protection, reverse connection protection, and power-off protection. The CC/CV method itself guarantees that the charging will not be overcharged or overcurrent. In the design of the circuit in Figure 2, there are two points that I feel more proud of: 1. LED1 and LED2 are both 'AND gates' Logitech. 2. The full charge indication has nothing to do with the current setting value. It is up to 5% of the maximum charging current. Some people feel uneasy: 1. LED2 must be red, and the voltage drop under 5mA should not exceed 1.8V, otherwise the short-circuit current (designed Small) still large. 2. It is still a bit more complicated (mainly considering the simplification under the premise of ensuring performance and function). u003c/pu003eQ: So, will LM324 be replaced with IM339 soon? Also, how to do that current source? Is it really a constant current circuit? A: Yes, LM324 and LM339 are common. At first I did use OC’s LM339 to solve the 'or' relationship, but then I plugged in the LED and found that LM324 can also be used, and I only have LM324 on hand. If I omit the charge indicator function (Many chargers do not have or are not real, such as Scud), you can use the 8-pin dual comparator LM393, and you can save the other 4 components. The current source can do this: 1. Use the finished current source, I have two in my hand. 2. Use a low-power junction field effect tube to directly connect S and G (ie source and gate) together. 3. Use 1 diode, 2 resistors and a PNP transistor. If you don't need a constant current source, you can make do with it, and change it to a shopkeeper (1KΩ), but the effect is worse. Q: Is the charging current of this circuit also 0.6A? How long will it take to charge a 7.2V, 1360mAh lithium battery pack? A: The current can be adjusted by the owner. When it is adjusted to 700mA, it takes more than two hours to fully charge. Generally, the charging current is 0.5C. If it is too large, it will ignore the service life. If it is too small, the charging time is too long. If you don't mind the long charging time, the current can also be made smaller. For a 1360mAh battery, 0.5C current is 680mA. Q: What is the final discharge voltage of a single-cell lithium battery pack? A: Single-cell lithium battery pack, nominal 3.6 or 3.7V, the century voltage is higher than this in most occasions, fully charged to 4.2V, and will not decrease after being placed, the normal discharge voltage is 4.1~3.6V, which is lower 3.6V, sometimes electrical appliances (such as digital cameras) will show that the battery is low, and when it reaches 3.1-3.2V, it will simply shut down automatically. Although some lithium battery manuals state that the minimum discharge voltage is 2.75V, it generally refers to high current applications. Although the operating voltage of the internal discharge protection circuit of many lithium batteries is 2.5V, that is an extreme situation, and lower than 2.5V will cause great and permanent damage. In fact, if a single voltage is lower than 3.3V, the discharge curve drops very quickly, which has no practical value. Therefore, it is recommended that the discharge end voltage is 3.2V. If high current discharge (about 0.5C), the stop voltage can be lower. u003c/pu003e
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