Samsung KCT52A, Training Manual

Page: 11 / 93

KCT52A Chassis
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11
Power Supply Description Off-Time Control Circuit Description
The INH voltage is used as the input signal to the COMP1
and COMP2 within the control IC.
When INH voltage reaches Vth1, the OSC output is kept low,
so PTR maintains off mode. (Fig. 1)
When INII voltage reaches Vth2, the output of the COMP2
reverses and tile voltage of C2 starts to discharge rapidly. If
the INH voltage does not fall below Vth2, tile C2 voltage will
be kept to almost 0 V, and tile PTR will remain off mode.
(Fig.2)
When the PTR is off, the primary energy is transferred to the
secondaries including DI winding, which voltage is set to
higher volatile than Vth2 in normal operation.
This transferred energy starts charging Cinh through D3 and
Rinh. When INH voltage reaches Vth, C2 will discharge
quickly, and remain low even after the energy transfer is com-
pleted became the INH voltage does not fall instantaneously,
bid rather fall in decay fashion. This falling time duration
depends on Cinh,IC input impedance, mid INH voltage,
which is proportional to output load voltage.
Higher the load voltage (less load current) is, the longer the
falling time is because INH voltage is higher.
Fig. 1
Fig. 1