Boost output practical circuit

The picture shows a practical circuit with boost output. VT3 is a switching regulator tube; the voltage regulator tube VD2 can perform potential conversion; VT4 is an inverting isolation amplifier; VT4 and its load 33kΩ resistor divide Ui. These two voltages are supplied separately to the pulse generator circuit. The pulse generator circuit consists of transformer T, VTl and VT2. This is an asymmetrical transformer positive feedback self-excited multivibrator. The power supply of VTl is taken from the voltage on the 33kΩ resistor, and the current on the resistor depends on the current of VT4. The power supply voltages of the two tubes VT1 and VT2 are different. The amplitude of each half cycle of the oscillation changes in direct proportion, and the width changes in inverse proportion. Control VT3 turn-on and cut-off time. When the output voltage increases, the current of the differential pair tube VT6 of the error amplifier increases, the current of VT5 decreases, the collector potential increases, the current of VT4 increases, the voltage drop across the 33kΩ resistor increases, and the supply voltage of the VTl tube increases, resulting in The conduction time is shortened, and the conduction time of switch tube VT3 is shortened. According to the boost output voltage expression , it can be seen that the output voltage Uo decreases to achieve voltage stabilization. On the contrary, when the output voltage drops, the above process is adjusted in the opposite direction to make the output voltage rise again and maintain the output voltage stable. The input voltage of this circuit is 12~28V, the output can be stable at 30V, the maximum output power is 60W, the efficiency is 89.4%~94.7%, the instability is ±0.33%, the output voltage pulsation coefficient is O.02%, and the operating frequency is 10kHz.