One of the VMOS tube switching regulated power supplies

The picture shows a regulated power supply circuit using a VMOS tube as a switching device. In the figure, VT5 is a VMOS power transistor, which is the power switch adjustment device; L1 is an energy storage inductor; VD3 is a freewheeling diode; VT3 is a field effect transistor, which serves as the constant current source of VTl and VT2, providing lmA to their emitters. constant current; Cl is the input filter capacitor; C5, C6, and C7 are the output filter capacitors. Which tube, VTl or VT2, is turned on first depends on the relative voltage of the bases of the two tubes. If the base potential of VT1 is lower than the base potential of VT2, VTl is turned on and VT2 is turned off; if the opposite is true, VTl is turned off and VT2 is turned on. The base potential of VT2 is determined by the resistors R2, R3 and the Zener diode VD1, and is a constant; while the base potential of VT1 is obtained by dividing the output voltage through the voltage dividing resistor R6C R and the potentiometer R8. Adjusting the potentiometer R8 can Change the output voltage. In order to reduce the power consumption of the switching regulator VT5 and increase its flip speed, the circuit uses a bootstrap network composed of R5 and C4. When the network is cut off at VT5, the source potential is 0V, and the input voltage charges C4 through the diode VD2 and the resistor R4, making the voltage on C4 close to the input voltage. After VT5 is turned on, the source potential increases. Since the capacitor C4 is charged with voltage, the diode VD2 is cut off. At this time, the voltage on R5 is close to twice the input voltage, making VT5 turn on faster. At this time, even if the input voltage is relatively low, the circuit can flip reliably. The function of C2 and C3 is to enable VT1 and VT2 to flip quickly to increase the switching speed. When the output voltage U0 increases for some reason, the base potential of VTl rises accordingly, causing VT2 to turn on, and further turning on VT4. The gate potential of VT5 drops and then turns off. At this time, the current in the energy storage inductor L1 decreases, causing the output voltage to decrease. When the output voltage is lower than the rated value, VTl is turned on, VT2 is turned off, and the two tubes flip. Therefore, VT5 is turned on due to the increase in gate potential, the current in L1 increases, the output voltage increases, and the circuit enters the next cycle. In other words, the circuit enters an oscillation state from now on, and its oscillation frequency is 100kHz. The rated output voltage of this power supply is 5V, the output current is 1A, the power efficiency is 80%, and the operating frequency is l00kHz.