Tatung_TM01_Monitor.pdf | | SECTION
3
ISOLATED SWITCHED-MODE P O W E R SUPPLY
3.1.
CIRCUIT DESCRIPTION _I .
The power supply is a self-oscillating switching type of converter which, under normal conditions, operates at a free-running frequency l of between 20 and 3OkHz. A l control functions are performed within 1801 (TDA4600). The output transistor, Q801, switches the primary winding of the transformer, T801, across the rectified mains voltage developed on the reservoir capacitor, C804. The output voltages, (121V and 18V, are generated at taps on the secondary winding and rectified and smoothed by D812, D811, C822, C826 and C821. The base drive for Q801 is generated in I801, the current at pin 8 controlling the switch-on period and that at pin 7 controlling the turn-off conditions of Q801. R808, R810 and C813 develop a sawtooth voltage at pin 4 which simulates the collector current of Q801. This is used to generate a sawtooth base drive at pin 8 to avoid over-saturation of Q801. 0803 and C314 rectify and sm |