Boost switching power supply composed of NE555

As shown in the figure, this is a step-up switching power supply circuit composed of 555. In the circuit, transistor BG1 is used as a switch adjustment tube; operational amplifier IC1 constitutes a comparison amplifier; 555 time base circuit is connected as an astable multivibrator. The oscillator generates a sawtooth wave voltage (Vmin=1/3Vz, Vmax=2/3Vz, the frequency is determined by W1 and C1) on C1 and sends it to the non-inverting input of comparator IC1, and the sampling voltage is sent to the inverting input of the comparator. The duty cycle of the rectangular waveform output by IC1 is controlled by the sampling voltage. When the output voltage is a stable value, the sampling voltage is a value between 1/3Vz and 2/3Vz. When the output voltage rises (or falls) for some reason, the sampling voltage rises (or falls) accordingly, so that the duty cycle of the rectangular wave output by IC1 decreases (or increases), the conduction time is shortened (or increased), and the output voltage decreases (or increases), thereby achieving the purpose of stabilizing the output voltage. By adjusting W, the size of the output voltage can be controlled.