Service manual

Principles of Operation
The +5 VDC regulator circuit has a built-in oscillator. External components
connected to pins 2 and 3 determine the oscillation frequency. R105 and C34
cause the circuit to oscillate at about 30 KHz. Figure 2-16 shows the oscillator
waveform.
Figure 2-16. Oscillator Waveform
AMP1 in the +5 VDC regulator circuit is an error amplifier that monitors the
output voltage. Figure 2-17 shows the constant voltage control circuit. Pin 1 of
the +5 VDC regulator circuit provides a 5 V reference output (Vref). Vref is
applied to the negative terminal of AMP1. The error amplifier adjusts its output
according to the voltages at its positive and negative input terminals. This keeps
the positive terminal voltage at 5 V.
Figure 2-17.
Constant Voltage Control Circuit
LQ-200/AP3000
2-17