Stabilizing Circuit - Toshiba DP120F Service Manual

7.2 Stabilizing Circuit

07-07-02
Fig. 7-7-3
The stabilizing circuit monitors the 5VPS voltage in the secondary circuit of the transformer
(T1) through the shunt regulator (IC1) and feeds back its status to the primary circuit through
the photo-coupler (PC2) to stabilize the power output.
IC1 compares the voltage produced by dividing the 5VPS power output through R18, R19 and
VR1 with the reference voltage. When the 5VPS voltage rises, the cathode current of IC1
changes to allow current to flow through the LED of PC2. This causes the light detector of PC2
to conduct to turn on Q2 so that Q10 will turn off due to a drop in its gate voltage and cut off the
current in the primary circuit of the transformer. When the current in the primary circuit is cut
off, the emission power of the secondary circuit will drop to decrease the output voltage for
stabilization.
March 2000 © TOSHIBA TEC 7-97 DP120F/DP125F Circuit Description