8V DC Power Supply With Over Voltage Protection

Posted on Feb 7, 2014

This 8V DC power supply was designed for use with an expensive piece of electronic equipment. It features full over-voltage protection as a precaution against regulator failure, either in the supply itself or inside the equipment it is powering. The circuit uses a conventional full-wave rectifier, followed by a 3-terminal voltage regulator (REG1)

8V DC Power Supply With Over Voltage Protection
Click here to download the full size of the above Circuit.

with appropriate filtering. When power is applied and switch S1 is in the "Run" position, REG1s output is fed to the load via a 500mA fuse and Schottky diode D3. This also lights LED2 (yellow) and LED3 (green), which respectively indicate the presence of the unregulated and regulated voltages. D3 is there to protect the circuit against external voltage sources (eg, charged capacitors). A "crowbar" circuit comprising ZD1 and SCR1 provides the over-voltage protection. It works like this: if a fault develops (eg, REG1 short circuit) which causes the output voltage to rise above 9. 1V, ZD1 turns on and applies a voltage to the gate of SCR1. If the voltage then continues to rise, SCR1 turns on (at about 10V) and "blows" the fuse. Zener diode ZD2 provides emergency over-voltage protection in case the "crowbar" circuit develops a fault. Switch S1 is provided so the operator can occasionally test the "crowbar" function. When S1 is switched to the "Test" posi ­tion, the load is disconnected by S1b and the unregulated supply voltage is applied by S1a to the "crowbar" circuit, thus causing it to trigger. When this happenS, LEDs 2 & 3 (green and yellow) extinguish and LED1 (red) lights to indicate that the SCR has triggered. The SCR turns off again when S1 is switched back to the "Run" position.

Leave Comment

characters left:

New Circuits



Popular Circuits

12V White LED Driver
LED Ultraviolet exposure box
TLE5206-2 H-Bridge Circuit Application and Datasheet
remote control using the ne 555 and lm 567
The method of temperature controlling system of producing one-chip computer calorstat is analyzed
decibel meter circuit
ir sensors from scratch line follower
temperature sensor circuit
Simple UPS
Energy Saving Lighting with One-Shot Timer Circuit
Converting an EV PL-76 or 1776 microphone to p48 powering
12V battery production controller