Regulator Circuit - Epson LQ 1050 - B/W Dot-matrix Printer Technical Manual

2.3.2.4 Chopper-Type Switching Regulator Circuit
A chopper-type switching regulator is employed in the power supply circuit. Operation of the step-down
circuit is as follows:
V I
Figure 2-14 shows the chopper-type, step-down switching regulator circuit. When the transistor is ON,
Vi is applied to coil L and capacitor C, and load current IL flows. At this time, electromagnetic
voltage
energy WL is accumulated in choke coil L. When the transistor turns off, WL is applied to the load via
flywheel diode D so that output voltage Vo becomes the average value:
Therefore, Vo can be held constant by controlling Ton. Figure 2-15
Voltage between the collector
and the emitter of Tr
,
T r
D
Figure 2-14. Step-Down Circuit
where, T = Ton + Toff (T is constant)
T
Current at diode
- — l— ,
(
ILO =
-
Figure 2-15. Step-Down Timings
2-18
t
L
Vo< VL
T
shows the step down timings.
when It is reverse recovered. (-'
D
*'ON
L