Practical circuit of non-isolated switching regulated power supply

As shown in the figure is a practical circuit without isolation of switching power supply. It is used as a switching power supply for Mudan brand TC-483D color TV. It includes a grid filter composed of C80l, C802 and L801; a bridge composed of VD80l and VD802 Type rectifier circuit; filter composed of R802 and C807; peak voltage limiter borne by varistor VD811; pulse oscillator composed of switching tube VT80l, pulse transformer T801, etc.; pulse width modulator composed of VT802, etc. ; Error amplifier composed of VT803, etc. It is easy to see from the figure that after the converted 220V voltage is rectified and filtered, it is directly connected to the output end through the primary winding of the pulse transformer T801 and the switching tube VT801 without isolation. This power supply has three sets of DC voltage outputs: 16V, 50V and 113V. The 113V DC output voltage supplies power to the load when VT80l is turned on, while storing electrical energy in C814 and magnetic energy in T801. When VT801 is cut off, the N1~N3 windings generate left negative and right positive induced voltages, causing VD805 to conduct forward bias. The energy stored in the transformer supplies power to the load and charges C814; C814 and L80l form a filter circuit to make the 113V output voltage continuous. smooth. The 50V voltage transformer, rectifier, and filter circuit is composed of TOl's N5~N6 windings, VD804, R805, C809, etc. C817 is a high-frequency bypass capacitor. The 16V output voltage transformer, rectifier, and filter circuit is composed of N5~N4 windings, VD803, R804, L803, C808, etc. C816 is a high frequency bypass capacitor.