Genicom MatrixPrinter LA36 - Manual (Page 127)

5-40
5.3.10 Power Supply
There are two types of power supplies:
100-120 VAC input: 29-33026-01 (PW31AA)
220-240 VAC input: 29-33027-01 (PW31BA)
The power supply output voltage is +5 V for the logic circuits and +34 V for the printer mechanism drivers
(Figure 5.41).
AC input from the power connector via the power-on switch is converted to DC by rectifier and smoothing
circuits. The amount of surge current is limited by the surge current prevention circuit. The DC is converted to
a high-frequency on/off voltage by the main switching circuit. The on/off voltage is reduced to +5 V and +34 V
by the step-down transformers. These voltages are then rectified and smoothed again.
The power supply's power stop control circuit turns off +5 V and +34 V power if an overcurrent or overvoltage
occurs, or the external signal PWSTOP is received from the control board.
(1) Surge current prevention (Figure 5.41 A)
When power is turned on, the charge current flowing into capacitor C3 is limited by the negative temperature
NTC thermistor (power thermistor). The power thermistor resistance is a few ohms at room temperature and
this initial resistance suppresses surge current. After initial transition, the thermistor becomes hot and its
resistance value becomes about 1/10 of the initial value. It does not suppress current in the steady (hot) state.
When the power is turned off and on simultaneously by the user or a instantaneous power drop on the AC line,
this system has a little effect to suppress inrush current because the power thermistor is still in a hot condition.
(2) Rectifying and smoothing (Figure 5.41 B)
The full-wave rectifier charges C03, generating DC between the DC+ and DC– terminals of C03 (Figure 5.40).
AC input
Thermistor
Rectifier circuit
C03
Figure 5.40 Surge current prevention circuit