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BD101 is a rectifier in which there are 4 build-in diodes, inverting AC to DC. CP110,CP111
is used to smooth the wave from rectifier. FR801 is a fuse resistor to protect the following circuit
when inrush current is too large.
UM102 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 two half-wave rectifier diodes
further to provide lossless startup circuit. Max start-up current for UM102 is 10mA, When current
flow from two half-wave rectifier diodes through RM107 and RM111 gets to HV pin to start up
UM102, Meanwhile, the VCC supply current is as low as 550uA thus most of the HV current is
utilized to change the VCC capacitor CM123, When Vcc (Pin6) reaches UVLO(on) threshold ,The
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