VMOS tube switching regulated power supply application circuit 2

The picture shows another VMOS tube switching regulated power supply circuit. Due to the use of voltage comparator 710, this circuit is simpler than the former. In the figure, the resistors R1, R2, R3 and the voltage regulator tubes VDl and VD2 form a voltage dividing and stabilizing circuit. Three groups of voltages of 5V, 6V and 18V are divided from the 28V input voltage as the power supply of the 710; resistors R12, R13 and capacitors C13, diodes VD6, VD7 and transistor VT3 form a power supply soft start circuit. At the moment when the power is turned on, the driving pulse width of the VMOS tube VTl can be increased exponentially. In this way, when the comparator 710 turns off the driving pulse for the first time, it can prevent the current of the energy storage inductor L1 from being too large. When the switch VTl is turned off, the output voltage of the switching regulated power supply continues to rise, because the current of the energy storage inductor L1 continues to charge the output filter capacitors C6~C12. In other words, the soft-start circuit slows down the rise of the current in the energy storage inductor L1 when the power supply first starts working, preventing the output voltage from large overshoot. When the regulated power supply enters a stable working state, the soft-start circuit will no longer work. The rated DC output voltage of this power supply is 5V, the output current is 10A, and the operating frequency is 200kHz.