Switching voltage regulator circuit of Lesheng DVD-883E ultra-thin DVD player

Switching voltage regulator circuit of Lesheng DVD-883E ultra-thin DVD player

Shown is the switching regulated power supply circuit of Lexus DVD-883E ultra-thin DVD player . It is mainly composed of AC input and rectifier filter circuit, switching oscillation circuit, secondary output rectifier filter, etc.     1. AC input and rectifier filter circuit     The AC input circuit is composed of power switch sw, fuse FI, mutual inductance filter Tl and other parts. The 220 V AC voltage is filtered and rectified by a bridge rectifier circuit composed of bridge rectifier stack VDI~VD4 and filter capacitor cl, and then outputs a DC voltage of about 300 V and sends it to the primary winding Li of the switching transformer.     2. The 300 V DC voltage of the switching oscillation circuit     is added to the ⑤~@ pins of IC1 through the primary winding Li of the switching transformer T2. The @~@ pins are internally connected to the drain of the switching field effect transistor. At the same time, the 300 V DC voltage forms a starting voltage through Ri, R2, M and other components and is applied to pin ① of IC1, causing the oscillation circuit in IC1 to start oscillating, and switching current begins to be generated in the primary winding of switching transformer 12.     The secondary winding I4 of T2 will induce a switching signal. The output of the L2 winding is rectified, filtered and stabilized to form a positive feedback signal and superimposed to the ① pin of IC1, keeping the ① pin with sufficient DC voltage to maintain the oscillation circuit in IC1. Oscillation brings the switching circuit into a stable oscillation state.     3. The output of the secondary winding (L3, L4) of the secondary rectification output circuit switching     transformer T2 outputs +12 V, -12 V, +5 V and other voltages respectively after being rectified and filtered by the circuit. The error detection circuit is located in the +5 V output circuit . Two voltage dividing resistors Rl4 and Rl{ are connected in series between the +5 V output terminal and the ground. The voltage dividing point is used as the error voltage sampling terminal, and the sampling voltage is added to the IC3 R input terminal. Optocoupler IC2 is connected to the K terminal of IC3. When the output voltage changes, it will cause the luminous intensity of the light-emitting diode in IC2 to change, which will cause the impedance between the collector and emitter of the photosensitive transistor in IC2 to change. The ◎ terminal of IC2 is connected to the @ and ④ pins of Icl. The ② pin of IC1 is the input terminal of the voltage stabilizing negative feedback signal. This loop regulates the output voltage.