Battery discharge indicator (batteries). Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells
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The indicator circuit (see figure) works as follows. When the battery voltage is normal, a current passes through the zener diode VD1, a voltage drop is formed across the resistor R1, sufficient to open the transistor VT1.
The collector voltage VT1 is small, and as a result, the transistor VT2 is closed. The RC generator assembled on the elements VT2, VT3, R4, C1, R5, R6 does not work, and the HL1 LED is constantly on, since the current of the open transistor VT1 passes through it, and in this situation HL1 acts as an indicator of normal supply voltage.
When the supply voltage of the battery (accumulator) decreases to the stabilization voltage of the Zener diode VD1, it practically does not pass current, and the transistor VT1 closes. The voltage on its collector rises almost to the voltage of the power source, through the resistor R4 this voltage is applied to the base VT2, and the RC generator starts to work. The current pulses of the RC generator pass through HL1, and it starts flashing, informing about the voltage drop below the set value. With the parameters R4, C1, R6 indicated in the figure, the blinking frequency is about 2 Hz (obviously, it is the frequencies of 2-4 Hz that act most excitingly on the central nervous system, in this case through the organs of vision, and cause alarming associations that are perceived as emergency signal).
If there is no need for HL1 to glow at normal voltage (so that the circuit consumes less current), you can increase R3 by about 10 times. In addition, it is possible to make the transition of VT2 from closed to generation mode more clear, you need to turn on the diode between the emitter VT2 and HL1, and reduce R5 to zero (shown by a dashed line). In this option, the current consumption can be less than 1 A, since the duty cycle of the generator pulses is about 10.
The circuit is also convenient in that it has only two outputs, as it is connected in series with the power source and HL1. It can be assembled into a small battery-like capsule, especially if surface mount parts are used. Transistors can be any npn and pn-p type, respectively, in terms of parameters, close to those shown in the figure.
Author: V.D. Borodai
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