Audio Engineering

320 Chapter 10

The basic series Class-G with two rail voltages (i.e., four supply rails, as both voltage
are ) is shown in Figure 10.3. 9,11 Current is drawn from the lower V 1 supply rails
whenever possible; should the signal exceed V 1 , TR6 conducts andD 3 turns off, so the
output current is now drawn entirely from the higher V 2 rails, with power dissipation
shared between TR3 and TR6. The inner stage TR3, TR4 is usually operated in Class-B,
although AB or A is equally feasible if the output stage bias is suitably increased. The
outer devices are effectively in Class-C as they conduct for signifi cantly less than 50%
of the time.

D 1

Inner driver

TR1

Vbias

2

Vbias

2

Vbias3

V 2 

50 V

V 1 

15 V

15 V

V 1 

50 V

V 2 

Outer

power

device

TR6

D 3

Inner

power

TR3 device

Vin

TR2

TR4

R 3

100R

R 1

200R

R 2

100R

TR7

D 2

TR8

D 4

Re

0R1 Rload

8R

Re

0R1

Vbias4

Figure 10.3 : Class-G-series output stage. When the output voltage exceeds the

transition level, D 3 or D 4 turn off and power is drawn from the higher rails through

the outer power devices.