Haier HS-2190, Руководство по обслуживанию

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(7) Power supply circuit
The power supply circuit of Hs-2129 is a typical free-running pulse width switch power
supply. The structure of the main circuit belongs to step-down type. It is a cold mechanism
power supply. The circuit is mainly composed of switch tube V503, exciter tube V502,
switch transformer T501 and rectifying filter circuit. The AC220V power voltage is rectified
by TD2SBA60 and smooth filtered by C507 and voltage about DC 300V is got. The voltage
is added to the collector electrode of switch tube V503. V503 and the primary group 3-7 and
the feedback winding 1-2 of the switch transformer T501 form a free-running blocking
oscillator. About 560VP-P intermittent oscillation pulse is generated at the collector electrode
of V503, the pulse width of which is controlled by capacitance C515. The collector electrode
and emitter of V502 are merged between the base electrode and the emitter of switch tube
V503. The conducting state of V502, i.e., the current through V502 controls the conducting
time of V503. If the current through V502 is high, the conducting time of V503 is short and
the voltage low. If the current through V512 decreases, i.e., the shunting effect decreases, the
conducting time of V503 is long and the voltage high. The working status of V502 is
controlled by the control circuit composed of V506, VD512 and N501. Direct sampling is
adopted for the control circuit and the photocoupler transmits error information. V506is error
comparison amplifier. N501 transmits error information. The error information changes the
current through V506 and the change generates error voltage on resistance R505 to control
the conducting state of V502, thus the conducting time of V503is changed and the purpose of
width is achieved. When the output DC voltage B1-115V increases, the current through V506
increases by the photocoupler, so the current through V502 increases, making the conducting
time of V503shorter, output voltage lower, thus achieving the purpose of regulation, and vice
versa. With VD513 rectification, C531 filtering and V552 control, the pulse voltage supplied
by the secondary pole of the switch transformer becomes 26V, which is supplied to vertical
scanning circuit. With VD515 rectification, C541 filtering, 15V voltage is obtained, which is
then regulated through three-stage adjustment to become the 12V, 9V and 5V voltage
supplying to the main chassis circuit.
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