Question

In a transistorized series regulator, how is the overload and short-circuit protection provided?

(a) By the use of a thermistor

(b) By using two additional diodes and a current sensing resistor to protect the series transistor

(c) By using a diode and an additional resistor to protect the transistor

(d) By using a diode along with a capacitor of a small capacitance value in series

This question was addressed to me during an interview.

I'm obligated to ask this question of Voltage Regulators topic in section Regulators of Analog Circuits

Answer 1

Correct choice is (b) By using two additional diodes and a current sensing resistor to protect the series transistor

For explanation: Series transistor can be protected by connecting two additional diodes and a current sensing resistor to the circuit. When the load current is smaller, the diode is off and load current is through the transistor and the new resistor. When the load current increases, the voltage drop across the new resistor increases and soon the diodes start conduction. A limiting current flows through the transistor.