The reference source of the power supply is to provide a stable, standard voltage source. Switching power supply now adopts PWM (Pules Width Modulation), that is, pulse width modulation circuit, whose function is to detect the output DC voltage, compare with the reference voltage, amplify, control the pulse width of the oscillator, and then control the push-pull switch circuit to maintain the stability of the output voltage.
The switching circuit is generally completed by TL494 or KA7500 chips, both of which are integrated with a 5V reference circuit with an accuracy of ±1%.
The positive and negative voltage sampling feet of the chip detect the change of the output voltage at any time, compared with the reference voltage inside the chip, the output error voltage and the oscillation pulse of the sawtooth wave generating circuit inside the chip are compared and amplified in the PWM (comparator), so that the output pulse width changes and the output voltage is controlled within the range of the standard value.