3V battery low indicator. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells
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The proposed device allows you to monitor the state of the battery and, when the voltage on it drops below 2 V, signal the need for urgent recharging. In this case, the LED starts flashing with a period of about 2 s. The indicator can also be used in other devices if it is required to control the voltage and signal its decrease below a predetermined level. It is only required to select the threshold.
The battery voltage is supplied to the input of the indicator and through a non-linear voltage divider R1-VD1-VD2-VD3 to the base of the transistor VT1. Divider elements determine the threshold for the indicator. As long as the input voltage exceeds 2 V, the transistor is on and its collector is low. When the input voltage becomes less than 2 V, the transistor VT1 closes, a high level appears on its collector. Transistor VT2 inverts the logic level from the collector VT1, i.e. when VT1 is closed, it is open, and vice versa.
A signal from VT2 starts a multivibrator on transistors VT3 and VT4. The multivibrator starts when the VT2 collector is low (high on the VT1 collector), i.e. at an input voltage less than 2 V.
When the multivibrator is operating, transistors VT3 and VT4 are either closed at the same time or simultaneously open. When the transistors are closed, the capacitor C1 is charged within a few seconds through the transistor VT2 and resistors R3, R4, R6. When VT3 and VT4 are open, capacitor C1 is discharged through the emitter-base junction of transistor VT3, resistor R4 and VT4. The open transistor VT4 turns on the HL1 LED. A current pulse flows through the HL1 LED, the value of which is determined by the type of the LED and the resistance R7 (up to 20 mA). The current is set to the minimum possible value, but so that the glow of HL1 is noticeable.
Literature
- Radiomir 2011 №4
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