Epson L-1000 Technical Manual page 52

REV.-A
AMP 1 in the IC is an error amplifier used to monitor the output voltage. Figure 2-17 shows the constant-voltage
control circuit. Pin 1 of the IC provides a 5 V reference output (Vref), which is applied to the negative terminal
of AMP 1. The error amplifier adjusts its output according to the voltages applied to the positive and negative
input terminals. This has the effect of maintaining the voltage at the positive terminal at 5 V.
Figure 2-18 shows the output from AMP 1. When the voltage at pin 4 becomes higher than that at pin 5 (over
voltage), AMP 1 outputs current modulated by pulse-width modulation (PWM) to reduce the output voltage of
the circuit. PWM is described below.
Figure 2-17. Constant Voltage
R108 and C35 compensate for phase lag in the error amplifier to prevent abnormal oscillation.
LQ-500/ L-1000
Control (+ 5 VDC)
PRINCIPLES OF OPERATION
Figure 2-18. AMP 1 Output
2-15