ViewSonic E95 - Page 47

E95-1 circuit description
4. CIRCUIT DESCRIPTION
4.1 POWER SUPPLY (switching mode power supply fly-back type)(IC101)
The raw DC B+ voltage is got from AC input voltage after CR101 rectifier. It supplies lower voltage VCC to
PWM controller, IC101 (KA2S1265), through start-up circuit (R104, R120, ZD101, Q102, D113). IC101 is
synchronous by T103/Q105/Q109/C110 switching frequency. In order to meet E2000 power consumption
specification, during power off mode, IC102 is turned off and Q116 is turned on. It can pull low IC101 pin4
feedback signal to forced power supply shut down. High-frequency & High-Voltage square wave-form is across
the primary winding and transfers energy to the secondary. The output DC voltage gets after rectifying and
filtering.
In order to have a stable and regulated output voltage while AC input voltage and output load change. IC203
will produce a current change through IC104 couple a voltage change on IC101 pind. PWM controller circuit
will change duty cycle and maintain stable voltage.
The PWM controller IC101 is started up from the raw B*. The lower voltage VCC is provided by T101's
AUX-Winding (pin1) through R151, D105, C108, SW101 to IC101 pin3.
The 198V in TP201 can be determinate by R211,R212,R223, VR201
(Vo=2.5 * (R211 + R212 / VR201 + R223).
Degauss CKT: When the power is turn on or press manual degauss let IC303 pin13 will high to turn on
Q209 and RL201, degauss will active about 4 second.
_ ViewSonic Corporation