Switching power supply circuit of Jieke GK-310A DVD player

Switching power supply circuit of Jieke GK-310A DVD player

The switching power supply circuit of Ke GK-310A DVD
player is as shown in the figure.     1. The AC
    220 V voltage of the switching oscillation circuit is rectified and filtered, and the approximately +300 V DC voltage obtained is divided into two paths: one path passes through the ①~③
windings of the switching transformer T and is sent to the ④ and ⑤ pins of Ul, and the other path passes through the starting resistor. R2 and R3 are sent to the ⑦ pin of U1 to charge the capacitor C7.
When the positive terminal voltage of C7 is charged to about 10 V, the internal oscillation circuit of Ul starts to work. The generated oscillation signal drives the field effect
switch to work in the switching state. There is a pulsating high-frequency current in the ①~@ winding of T. flow past. According to the principle of electromagnetic induction, the ④~@ winding of T generates
a high-frequency induced voltage. After the voltage is rectified by D5, current limited by R4, and filtered by C6 and C7, a DC voltage of about +14 V is obtained and sent to
the ⑦ pin of U] to provide the power required for normal operation of the internal circuit of U1, so that the switching power supply circuit can be stable Keep working. At the same time,
other windings on the secondary side of the switching transformer T also induce corresponding high-frequency pulse voltages.
    2. Voltage stabilizing circuit
    The voltage stabilizing circuit uses WIA31 (U3) and PC817 (U2). Its voltage stabilization process: When the output voltage increases for some reason
, the upper 5 V voltage increases accordingly, and the voltage at the voltage dividing point of the sampling resistors R12 and R13 (i.e., U3① pin) will also increase, thus When
the voltage of U3@ pin decreases, the brightness of the internal light-emitting diode of U2 increases, the internal resistance between the ce junctions of its internal phototransistors becomes smaller, and
the voltage of U2④qing decreases, that is, the voltage of U1② pin decreases. After the changing voltage value is processed by the voltage stabilizing control circuit inside the Ul② pin, the oscillation pulse width output by the internal
oscillator be narrowed, thereby shortening the conduction time of the field effect switch tube and the voltage output by the secondary output of the switching transformer. Then it decreases
and acts as a voltage stabilizer.
    3. Protection circuit
    R8, C8 and D6 in this machine form a peak absorption loop, which is mainly used to eliminate the reverse peak voltage generated by the leakage inductance of the switching transformer and
protect the field effect switch tube inside the power integrated circuit Ul from being broken down by the reverse peak voltage. And damaged. ZDI functions as overvoltage protection, and R6 and R7
function as overcurrent detection and overcurrent protection.
    4． The secondary output circuit
    switching transformer outputs a total of four sets of voltages (except for ④~@ windings). Among them, the high-frequency induced voltage generated on the windings ⑥~⑦ is rectified by D7 , filtered by C14, C15 and Ll to obtain a DC voltage of +5 V. This voltage is output in two channels: - channel is sent to the motherboard
through the CON3 and CON4 rows.
And display board: the other channel is stepped down by Dll and D12 and filtered by Cl6 to obtain +3.3 V DC voltage, which is sent to
the motherboard through the CON4 row to provide working power for the decoding circuit. At the same time, the +5 V DC voltage is also used as the sampling voltage of the voltage stabilizing circuit. @～◎
The high-frequency induced voltage generated on the winding is rectified by D8. After filtering by C17, C18 and L2, a DC voltage of +12 V is obtained to supply power to the audio power amplifier circuit.
◎~@The high-frequency induced voltage generated on the winding is rectified by D9. After filtering by C20, C21 and L3, a DC voltage of about -24 V is obtained, which
supplies power to the cathode of the fluorescent display screen. at the same time. This voltage is also stepped down by resistor R16, filtered by C19, and stabilized by ZD3, and then a DC
voltage of i2 V is obtained for use by the audio power amplifier circuit. @~@ After the high-frequency induced voltage generated on the winding
is rectified by Dl0, filtered by C22 and C23, and current limited by R22, a DC voltage of about 3.3 V is obtained at both ends of R18 to power the fluorescent display filament.