Main Ps Unit - JRC JRL-2000F Service Manual

The comparator IC5 detects an exccessive output valtage and sends out the
PS ALM signal via CD4 photocoupler. .· ..
R30 is a sensor which detects a MOSFET overheat. When the temperature of the FET
case exceeds 80
oc,
the terminal valtage of R30 increases and the transistor TAB is
turned on.
The circuit composed of IC2, TR6, TR7, T2
~nd
IC4 is a switching regulator which
generates a DC-12 V valtage.
2.3.3 CBG-68 Main PS Unit
The CBG-68 main PS unit is a regulator which generates a regulated output of DC 80
V (30A) based on the CBB-13 power factor corrector output of DC 350 V.
IC201 is a control IC and it sends out pulses for the 150 kHz switching control circuit .
MOSFETs TR205 and TR206 and transformes T202 and T203 compose a MOSFET
drive circuit for a main switching circuit and amplify two phase switching pulses from
IC201.
TR201 to TR204 arepower MOSFETs for a main switching circuit and compose of a
full-bridge switching circuit with an output transformer T201.
The output pulse from the secondary winding of T201 is rectified to DC by diades
CD301 and CD302, and smothed by capacitor C206.
R232 isasensor which detects apower MOSFET overheat of the main switching
circuit.When the temperature of the MOSFET case exceeds 80
oc,
the terminal valt-
age of R232 increases and transistor TR 209 turns on.
TS201 is a thermostat which detects overheat of the heat sink. lt turns on at
45
oc
and drives the cooling fan.
R231 is a resistor which detects a DC output current. The valtage detected by this
resistor is amplified by IC202 amplifier and it moves the pointer of the ammeter (ID) on
the front panel and at the same time detects an excessive current of the comparator
IC203. When the output current exceeds 30A, IC203 is turned on and it triggers the
control IC201 via the time constant circuit made up of TR207 and TR208 to terminate
switching oscillation .
At this time, the output of the transistor TR208 is applied to No.B pin of IC203 which
then issues an over current alarm.
The output valtage is divided by the variable resistor RV201 and resistors R233 to
R235 and the constant-voltage control by IC201 is achieved by the feedback of the
divided valtage to IC201.
The output valtage can be changed between DC 50V to BOV by adjusting RV201.
Resistars R236 to R238 divide the output valtage and the divided valtage moves the
pointer of the voltmeter (VD) on the front panel and activates the excessive valtage
detector circuit after entering No.1 0 pin of IC203.
When the outputvaltage exceeds 90 V, No.13 pin of IC203 becomes Low Ievei and an
alarm signal for an excessive valtage is issued. At the same time, the divided valtage
is also applied to No.6 pin of IC203 which then sends out the VPA ON RESP signal
indicating that the comparator outputvaltage is turned on.
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