overvoltage protection

An important feature on many power supplies is over voltage protection on the output. This is
particular important for 5 volt supplies which are used to power TTL logic circuits. These TTL
circuits have an absolute maximum supply voltage of 7.0V so that if, due to an internal fault
condition, the power supply output voltage were to rise above this voltage, all of the logic circuits
could be destroyed. This could be an expensive failure in a complex system.
To prevent this, an over voltage crowbar or clamp circuit can be used. A possible crowbar circuit
shown as below, uses a Zener diode, resistor, and a silicon controlled rectifier, or SCR. If the
output voltage for any reason exceeds the 6.2V breakdown of the Zener, a current flows through
the resistor producing enough voltage to trigger the SCR. When the SCR turns on, it places a short
circuit directly across the output, thereby protecting the load circuitry.
This short remains in place until the power supply is turned off and reset.
Sinpro product is designed by Crowbar Circuit.