Under and Over Voltage Protector (Power Guard)
A few circuits on under/over voltage protection have appeared recently in EFY. But this power guard circuit diagram is simple, very easy to construct and inexpensive. It can be added to existing stabilisers, in which case DC power supply can be taken from the original stabiliser circuit and only a few additional components, including one relay, are required to make the circuit.
| PARTS LIST | |
| R1 | 1KΩ |
| R2 | 820Ω |
| R3 | 10KΩ 1/2W |
| C1 | 1000µF 25V |
| C2 | 250µF 25V |
| VR1 | 4.7KΩ |
| VR2 | 4.7KΩ |
| T1 | HL100, SL100, BC547 or equivalent |
| T2 | HL100, SL100, BC547 or equivalent |
| RL | 12V 450Ω |
| Z1 | Bz148 or 6.8V Zener |
| Z2 | Bz148 or 6.8V Zener |
| D1 | BY126 × 4 or IN4007× 4 |
| T | 12V 500mA |
Above power guard circuit diagram has two preset potentiometers. When supply voltage is within limit, T2 conducting and T1 is in a non-conducting state. At low voltage, zener Z2 will not breakdown and T2 will not conduct, which results in de-energising the relay. This adjustment is done by adjusting VR2.
At high voltage, zener Z1 will breakdown and T1 will go in conducting state and the relay will de-energize. This adjustment is done by adjusting VR1. Normally-open contact of the relay is used in control circuit. Red LED gives high low voltage cut-off indication.
Please send your ideas, those are very important for our success…
Use a good macro mode camera for taking pcb images please. otherwise, good post
You have some nice posts. All the best,
Dear Sir,
May i have the value of the BZ148 as it is not possible to get it from the net.
Thanks,
Ananda
how the capacity in watt to lose operated
Яку напругу видає трансформатор?.
Іван.