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4) Quasi-resonant operation
By inputting a voltage signal which is synchronized with the energy discharge time of a secondary winding of a
transformer to the. INH terminal, quasi-resonant operation can be achieved. As shown in Fig. 8 , the voltage of
L1 winding which is synchronized. with the energy discharge time of a secondary winding. S1. shall be input to
the INH terminal through D805 and R807. Since V
shall be set at 2V.
Fig. 9 shows waveforms of V
output from the oscillator when operating in quasi-resonant mode.
when the power transistor turns off and a voltage higher than V
immediately discharges and then starts charging again. Even after the discharge of energy of a secendary
winding is completed, V
is determined by the production of internal impedance of the IC and C
D803
R807
9
VIN
6
INH
2
GND
, Ic and V
of the transistor, voltage across C808 in the oscillator as well as an
CE
INH
0V
INH Terminal
Voltage
0V
Fig 9 Waveforms of V
does not immediately increases. When it gets lower than V
INH
is set at 1.5V typical, a voltage at the INH terminal. V
TH2
D805
S1
L1
C808
Fig 8 Operation Circuit
V
CE
V
THI
tr
and V
at Quasi-resonant Operation
CE
INH
21
+
is applied to the INH terminal, C808
TH2
after the time,tr, which
TH2
, has past, the transistor turns on.
INH
,
INH
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