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How to Protect the Circuit from Battery Overshoot

Sep. 02, 2020

This circuit introduces a rechargeable battery voltage detection circuit made with a low-power operational amplifier LM393, which can monitor the voltage of the rechargeable battery in real-time. When the voltage of the rechargeable battery rises to the set value, the circuit can automatically send out a light alarm prompt and has a shutdown Turn on charging to protect the battery.


1. The working principle of the circuit

LM393 is a commonly used low-power dual op-amp, here only one of them is connected as a positive phase voltage comparator to monitor the voltage of the rechargeable battery. The 2V regulator tube in the picture provides a 2V reference voltage for the non-inverting input pin ③ of the LM393 here. Regulating resistor R is a sampling potentiometer, and the positive phase input terminal ② of LM393 monitors the voltage of the rechargeable battery through LM393.

The rechargeable battery monitored by this circuit is 12.6V. When the voltage of the rechargeable battery is lower than the set voltage of the circuit, the voltage of the LM393's positive input terminal ② is lower than the reference voltage of its ③ pin (2V), at this time the output of the LM393 output terminal ① pin is low and its LED is off, PNP transistor is cut off, the relay is reset, and the battery can be charged.

When the rechargeable battery is charged so that the voltage at both ends rises above the set value, the voltage of pin ② of LM393 is higher than the reference voltage of pin ③. At this time, the output of pin ① of the output terminal of LM393 becomes high level, and the LED lights up. The NPN transistor is saturated and conducted, the relay works, the circuit is disconnected, and the battery stops charging.

Rechargeable Battery

2. The choice of components

The adjustable resistor R on the circuit board is used to set the detection voltage of the circuit.

When making, the adjusting resistor R can be a 50K multi-turn fine-tuning resistor, and the voltage regulator tube is a 1N4615 voltage regulator diode with a voltage of 2V and a power of 0.5W. The LED uses a high-brightness red LED. PNP transistors can be S8550 and other PNP transistors. The relay can be a general 5V single-pole double-throw relay. The dual operational amplifier selects the low-power dual operational amplifier LM393 in a dual in-line 8-pin package. The operational voltage range of this operational amplifier is 2-36V.

3. Circuit debugging

When the input voltage of this circuit is above 12.7V, the LED will light up and the relay will be activated.

This circuit is used to monitor the voltage of a 12V rechargeable battery. When debugging, connect the adjustable power supply to the battery interface, adjust it to be lower than the set voltage, then adjust the variable resistance R until the LED lights up, adjust the adjustable power supply to a few volts lower than the set voltage, and the LED goes out . The adjustable power supply is disconnected and the battery can be connected at this time.

The information is provided by the battery supplier.