simple low/high voltage cut off circuit

Simple Low/High Voltage Cut Circuit



  Various safety circuit (low/high voltage cut) using IC is already published in www.electronicsproject.org. Now, here is very simple low/high voltage cut circuit using only two transistors.

  The entire circuit is build using only two transistor and very few other component. The two transistors are used to drive relay. Transistor T1 and T2 cut the supply in high and low voltage respectively. Variable resistor VR1 and VR2 is used to adjust the high and low voltage. As we know that when zener diode is connected to emitter of transistor then it get back bias voltage. The variable resistor VR1 and VR2 is so adjusted that it does not connect the transistor T2 and T1 in high and low voltage respectively. The load is connected through relay RL1.

Parts List

Resistors (all ¼-watt, ± 5% Carbon unless stated otherwise)

R1, R4 = 4.7 KΩ

R2, R3 = 220 Ω

VR1 = 10 KΩ

VR2 = 10 KΩ

Semiconductors

T1, T2 = BC148

ZD1, ZD2 = 5.6V

Miscellaneous

RL1 = 18V/500Ω