This universal power supply contains, beside the bridge rectifier, a voltage stabilizer (78xx) and a pnp power transistor. This combination allow a load current up to 5 A. As you know a voltage stabilizer in a TO-220 package can deliver up to 1A. The additional power transistor takes the load current of about 200mA.

This overvoltage protection or crowbar protection circuit is used where we need protection against high voltage surge. The circuit has a few components, it is very easy to build and will protect your electric equipment againg overvoltages. The crowbar circuit must be mounted between power supply and the protected device.