Q-In the IC 7805, what is the minimum input voltage for proper functioning?
a) 5V
b) 6V
c) 7V
d) 8V
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Answer: c
Explanation: For a fixed voltage IC regulator, the input voltage should be at least 2V greater than the output voltage. A minimum voltage of 2V should be allowed to drop in the internal circuit of the IC.
Q-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
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Answer: b
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
Q-What is not related to a transistorized series regulator?
a) The output can be varied by using a variable resistor
b) The output is independent of temperature
c) The overload and short circuit protection is not required
d) The circuit has negative feedback responsible for regulation
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Answer: c
Explanation: In a transistorized series regulator, the Zener diode maintains emitter voltage. An increase in output is canceled by a decrease in the output. The circuit has negative feedback for this regulation. The output may be varied by using a variable resistor and change in output due to temperature due to the Zener diode is canceled by the change in VBE of the transistor. However, when the load is reduced, or an accidental short-circuit occurs, overload and a short circuit occurs, and protection is needed to prevent that.
Q-In a power supply, the output voltage can vary due to multiple reasons. Which of these is not true if it is found that the output voltage is constant?
a) The voltage stability factor is very high
b) The output resistance is zero
c) The temperature coefficient is zero
d) The voltage stability factor is very small
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Answer: a
Explanation: In a power supply, the output voltage can vary due to changes in AC supply, load current and the temperature.
VO = f(VS, IL,T)
ΔVO = SV.ΔVS + ROΔIL + STΔT.
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