The invention discloses a DC-DC switch power soft-start circuit of digital-to-analogue conversion (DAC) control, comprising an oscillator, a counter, a digital-to-analog converter, an error
comparator, a PWM
comparator and an on-off controller. In the invention, a Q output end of the on-off controller is connected with a grid of an outer switch
rectifier tube, a QN output end is connected with a grid of an outer follow current tube, the output end of the PWM
comparator and the output end of the oscillator are connected with the input end of the on-off controller, the input end of the PWM comparator is respectively connected with the output end of the oscillator and the output end of the error comparator, one end of the input end of the error comparator outputs sample
voltage, the other end of the input end of the error comparator inputs the
voltage generated by the digital-to-analog converter, the output end of the error comparator outputs a difference value amplifying
signal of the sample
voltage and the voltage generated by the digital-to-analog converter, one end of the counter is connected with the output end of the oscillator, and the other end of the counter is a zero clearing
signal and outputs an 8-digit parallel
signal. When the power is electrified, the reference voltage of the input end of the error comparator is controlled to enable the reference voltage to rise step by step from small to large, and the voltage of the output end of the error comparator goes up slowly with the reference voltage, thereby avoiding overshoot voltage in the starting procedure and realizing the function of soft-start.