Switching regulated power supply circuit of Toshiba SD-K320 DVD player

Switching regulated power supply circuit of Toshiba SD-K320 DVD player

Shown is the switching regulated power supply circuit of Toshiba SD-K320 DVD player . As can be seen from the figure, it is mainly composed of AC input circuit , rectifier filter circuit, switching oscillation circuit, switching transformer T802, secondary rectifier filter and voltage stabilizing circuit.     (1) AC input circuit     The AC input circuit is composed of fuse F801, mutual inductance filter T801, filter capacitors CSOI~C804, etc.     (2) Rectifier and filter circuit     After filtering the 220 V AC voltage, a bridge rectifier circuit composed of diodes D802~D805 and filter capacitor C805 performs rectification and filtering , and then outputs a DC voltage of about 300 V and sends it to the ⑤ pin of the switching transformer T802 .     (3) Switching oscillation circuit     The switching oscillation circuit is mainly composed of JC803 and peripheral circuits. The oscillation circuit, voltage stabilization control circuit and switching field effect transistor are all integrated in IC803 (S-IR-F6535). After starting up, the 300V DC voltage output by the rectifier of the 220V AC voltage is added to the ③ pin of IC803 through the primary winding @~③ of the switching transformer T802, and the ◎ pin is internally connected to the drain of the switching transistor. At the same time as the power is turned on, the AC input voltage forms a starting voltage through R804 and is added to the ④ pin of IC803, causing the oscillation circuit in IC803 to start oscillating, and switching current begins to be generated in the primary winding of switching transformer T802.     The secondary windings ①~② of T802 will induce switching signals. The output of pin ② is formed by the rectifier and filter circuit to form a positive feedback signal and superimposed on pin ④ of IC803, so that pin ④ has enough DC voltage to maintain the oscillation of the oscillation circuit in IC803, so that the switching circuit enters a stable oscillation state.     (4) The secondary rectifier output circuit     T802 has multiple windings, and the output end of each winding is connected to a rectifier filter circuit, which outputs voltages such as lo V, 6.6 V, Sv, 11.8 V, -24V respectively.     The error detection circuit is set in the +10 V output circuit. The voltage dividing points of R826 and R827 are the voltage sampling terminals. The sampling voltage is added to the R input terminal of VT821. The photocoupler vr802 is connected to the C terminal of VT821. When the output voltage changes It will cause the luminous intensity of the light-emitting diode in VT802 to change, which will cause the impedance between the collector and emitter of the photosensitive transistor in VT802 to change. The ③ pin of VT8Q2 is connected to the ① pin of IC803. Pin ① of IC803 is the input terminal of the voltage stabilizing negative feedback signal. This loop regulates the output voltage.     (5) Start/standby control circuit The     start/standby control signal from the microprocessor is added to the ① pin of the photoelectric coupler VT804. The oscillation state of the switching power supply is controlled through VT804 to start and standby. In the standby state, the switching power supply is intermittent. oscillation.