Under and Over Voltage Protector
A few circuits on under/over voltage protection have appeared recently in EFY. But this circuit 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 | HL 100 |
| T2 | HL 100 |
| RL | 12V 450Ω |
| Z1 | Bz 148 |
| Z2 | Bz 148 |
| D1 | BY 126 × 4 |
| T | 12V 500mA |
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-energise. 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…
#1 by pasanlaksiri on April 24th, 2011
You have some nice posts. All the best,
#2 by Arup Basak on October 6th, 2010
Use a good macro mode camera for taking pcb images please. otherwise, good post