REV.-A
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:
–ton—
.U
*Z=ZZZ
,
/
o
i—-~
t
o
Tr
f
L
VI
D
c-:
T
Vo<
VL
o
Figure 2-14. Step-Down Circuit
Figure 2-14 shows the chopper-type, step-down switching regulator circuit. When the transistor is ON,
voltage
Vi is applied to coil L and capacitor C, and load current IL flows. At this time, electromagnetic
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:
V.
=
Vi X Ton
T
where, T = Ton + Toff (T is constant)
Therefore, Vo can be held constant by controlling Ton. Figure 2-15 shows the step down timings.
Voltage between the collector
and the emitter of Tr
V1-ve
o
Lo
- —
l—
,
Current at
diode D when It is reverse recovered.
(-’
‘mitterarrentOf
;omrEILO+
*’ON
“-
cuwentdD
m-”
Current”t’okecoi’
oz2rEs’::F
(
V1-vo)vo
L
ILO =
10
-
2Lt
V 1
Figure 2-15. Step-Down Timings
2-18
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