Audio Engineering

Power Supply Design 149

approach is to use a combination of avalanche diode and power transistor, as shown in
Figure 5.2(b). The obvious snag is that in order for such a system to work, there must be
a continuous current drain that is rather larger than the maximum likely to be drawn by
the load, which is wasteful. The main advantages of the shunt regulator system are that
it is simple and that it can be used even when the available supply voltage is only a little
greater than the required output voltage. Avalanche and Zener diodes are noisy, electrically

(a)

D1

V in

0V 0V

V out

Zener diode

Figure 5.2 : Simple shunt regulators.

R1

R2

D1

V in V out

0V 0V

Q1

Zener diode

(b)

D1

1N4148

D2

1N4148

D3

1N4148

V in V out

0V 0V

CC1

(c)