Xerox WorkCentre Pro 412 Service Manual page 102

Circuit Description
5-7-7-6 THV(THV(+)/THV(-) Output Unit)
Transfer(+) output unit is the transfer output control signal 'PWM-LOW ACTIVE'.
When THV-PWM LOW signal is received, Q203 turns on and the steady voltage will be accepted to the
non-inverting terminal of OP-AMP 324. As the voltage is higher than the inverting reference voltage of OP-
AMP, OP-AMP output turns high.
The 24V power adjusts the electric potential to ZD201 and ZD202, sends IB to TRANS auxiliary wire
through current-restricting resistance R215 via R212 and C204, and eventually Q204 will turn on. When
the current is accepted to Q402, Ic increases to the current proportional to time through the T201 primary
coil, and when it reaches the Hfe limit of Q204, it will not retain the "on" state, but will turn to "off". As Q402
turns 'off', TRANS N1 will have counter-electromotive force, discharge energy to the secondary coil,
sends current to the load and outputs THV voltage through the high voltage output enable, which is com-
prised of Regulation– circuit. The output voltage is determined by the DUTY width. Q203 switches with
PWM DUTY cycle to fluctuate the output by fluctuating the OP-AMP non-inverting end VREF electric
potential, and the
maximum is output at 0% and the minimum, at 100%.Transfer(-) output unit is THV-EA 'L' enable.
When THV-EA is 'L', Q302 turns on and the VCE electric potential of Q302 will be formed and sends IB to
TRANS auxiliary wire through R311, C305 and VR302 via current-restricting resistance R314, and eventu-
ally Q303 will turn on. When the current is accepted to Q303, Q303's Ic increases to the current propor-
tional to time through the T301 primary coil, and when it reaches the Hfe limit of Q303, it will not retain the
"on" state, but will turn to "off". As Q303 turns 'off', TRANS N1 will have counter-electromotive force, dis-
charge energy to the secondary coil, send current to load and output THV(-) voltage through the high volt-
age output enable, which is comprised of Regulation circuit.
5-64 3/03 WorkCentre Pro 412, FaxCentre F12 &
WorkCentre M15/M15i