4. CIRCUIT DESCRIPTION
4-1. POWER FACTOR circuit
Q
The full-wave rectified voltage waveform from D942 and smoothed voltage waveform from C926 are multiplied and
compared to
R
the voltage waveform from current detect resistor R925 of Q934. Q934 is turned off when
R
exceeds
Q
, and is turned on when
R
is 0V. The above repetition is to change input current to substantially
sinusoidal waveform and it corrects harmonic distortion. The switching frequency is not constant as Q934 is turned
on or off by monitoring input voltage and load current. Therefore, this circuit is not synchronized with the MAIN
POWER circuit.
Switching frequency is minimum when input voltage is low and load current is maximum, in other words, the
switching frequency is maximum when input voltage is high and load current is minimum. (Switching frequency is
approx. 20-250kHz)
This circuit is operated by the voltage supplied to IC932 from the SUB POWER circuit so that it is not activated at
power management state.
- 20 -
+400V
D942
IC932
7
Q934
AC
90-132/
198-264V
D943
R925
C926
R926
R927
R928
T932
POWER FACTOR circuit
5
0V
0V
0V
DC
To pin 1
of IC932
