Sharp LC-32SV40U Service Manual page 82

the gate drive signal , the high-voltage current source is then disabled ,and the Vcc supply current
is provided from the auxiliary winding of the transformer PIN8.
US101 Pin1 is protection PIN.RS105, RS105 are sense circuit, STR-A6069H detects the
MOSFET current, from the S/OCP in.When S/OCP pin over 0.9V, theUS101 will enter
auto-recovery type protection, Presenting a hiccup mode. The gate-out will not resume switching
until OCP falls below 0.9V.
A brownout comparator is implemented to detect the abnormal line condition.When pin1 fall
below 5.15v,the gate output will be kept off even Vcc has already achieved UVLO(on).Unless the
line voltage is large enough to pull pin1 larger than 5.2v,the gate output will not start switching even
when the next UVLO(on)is tripped.
US101 control 5Voutput ,DS106,DS107,CS109,CS110,CS111,CS112,LS101 are used to 5V
rectifier and smooth ,for system standby function circuit .
UL101 (SSS9512S) is a double-ended controller specific for the series-resonant half-bridge
topology.In these converters the switches QL101 and QL102 of the half-bridge leg are alternately
switched on and off for exactly the same time.
UL101 is a current-mode PWM controller with excellent power-saving operation, It features a
high-voltage current source to directly supply the startup current from bulk capacitor and further to
provide lossless startup circuit. Max start-up current for UL101 is 20mA, When current flow from the
bulk capacitor CP111 through RL101 RL102 and RL103 gets to HV pin to start up UL101,
Meanwhile, the VCC supply current is as low as 13uA thus most of the HV current is utilized to
change the VCC capacitor CL102, Whenever the VCC voltage is higher than UVLO (16V),the
GATE pin will output signal to drive the power MOSFET, the high-voltage current source is off and
the supply current is provided from the auxiliary winding of the transformer PIN16(VGH) and
PIN11(VGL).
When UL101 begins to operate Pin16 and Pin11 of UL101 will output square wave to drive
QL101 and QL102, then the main current flow get to GND bypassing through TL102, QL101 and
QL102 . Because of the change of current flow, wires in the other side of TL102 will induct current.
In the same time, the current inducted by wires which connected TS101 Pin 1/Pin2 and Pin 4/Pin5,
with components of QS102,QS101,QL104,and CL102 ,will be supplied to UL101 for normal
operating.
When QL101 & QL102 is turned on, the main current flow will be consumed through DL101,
DL102, RL108 RL109, RL110,RL113,RL111 and RL114, This will prevent QL101 & QL102 from
being damaged under large current impulse and voltage spike.
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