The integrated output amplifier described in this article consists of little more than one integrated circuit. It is intended especially for use in motor vehicles and other battery-operated applications. Although it appears simple and hardly worth looking at, the amplifier can produce an appreciable audio power output. The circuit diagram in Figure 2 emphasizes how few external components are needed to construct a complete output amplifier.
For instance, the new device does not need compensation networks to enhance the stability. Also, because of the absence of switch-on phenomena, there is no need for a switch-on delay network. There is, of course, still a need for supply line decoupling capacitors. Capacitors C5 and C6 are required for Class-H operation, about which more in the box. The value of input capacitors C1 and C2 is relatively low, thanks to the high input impedance of the IC. Switched RC network R4-C4 at the ‘mode select’ input (pin 4) serves to switch the IC to ‘mute’ or ‘standby’.
When the supply voltage is switched on, the IC is first switched automatically to the ‘mute’ mode and to ‘on’ only after a short delay. The time constant R4-C4 is a few tenths of a second and this delay between the two states is sufficient to obviate disturbing (and annoying) switch-on phenomena. Switch S1 enables the amplifier to be switched to ‘standby' when the use of the amplifier is not needed for a period of time. When that time has elapsed, the amplifier is quickly reverted to normal operation. The current drain in the standby mode is virtually negligible at only 200µA. Resistor R3 prevents a short-circuit current ensuing when S1 is being closed at the instant C4 is being discharged.
Measurement results (at Ub=14.4 V)
- 8–18 V
- 760 mV r.m.s.
- 70 kΩ
- 54 W r.m.s. into 4 Ω (f=1 kHz; THD+N=1%)
- at 1 W into 4 Ω: 0.046% (1 kHz)
- 0.29% (20 kHz)
- at 35 W into 4 Ω: 0.12% (1 kHz)
- 0.7% (20 kHz)
- 88 dBA
- 7.5 Hz – 185 kHz (at 25 W into 4 Ω)
- about 135 mA (‘on’)
- R1 = 1MΩ
- R2 = 4kΩ7
- R3 = 1kΩ
- R4 = 100kΩ
- C1,C2 = 470nF
- C3,C4 = 10µF 63V radial
- C5,C6,C8 = 4700µF 25V radial
- (18mm max. dia., raster 7.5 mm)
- C7 = 100nF, raster 5 mm
- D1 = high-efficiency-LED
- IC1 = TDA1562Q (Philips)
- S1 = single-pole on/off switch
- Four spade connectors, PCB mount Heatsink for IC1 (Rth<2.5 K/W)