Switching regulated power supply with isolated output and sampling windings

The picture shows a switching regulated power supply with output and sampling windings isolated. In the figure, T is the high-frequency transformer; N2 is the self-oscillation positive feedback winding; N3 is the winding that provides the sampling signal for the error amplifier VT3; N4 and N5 are the DC output windings. Since N3, N4, and N5 are isolated from each other, the DC output terminal and the power grid are also isolated from each other. This power supply has two sets of DC regulated outputs, 6.3V and 100V. The 35V voltage is for the error amplifier. When the output voltage rises, the voltage UD on the sampling resistor rises, and the collector current of error amplification VT3 increases. The voltage drop generated by this current on resistor R8 increases the forward bias voltage provided by rheostat VT2, causing the collector current of VT2 to increase. The voltage drop Ucd2 of its tube decreases, which is equivalent to the reduction of the shunt resistance between the base of the switch tube VTl and the ground, which accelerates the discharge current of Cll, shortens the conduction time of VTl, and narrows the output pulse width, causing the increased voltage to increase again. down, keeping the output voltage stable. In the same way, when the output voltage decreases, the opposite adjustment is performed according to the above process to make the dropped output voltage rise again.