Startup circuit and power supply circuit

A startup circuit comprising:

• an error amplifier that performs amplification of an error between an output voltage and a target voltage for the output voltage;
• a PWM comparator that compares an output signal of the error amplifier with a triangular signal and generates a PWM signal;
• a soft start circuit that charges a capacitor for soft start by a current source and delivers a terminal voltage with a shape of a slope developing across the capacitor as a target voltage in a startup period to the error amplifier;
• a detecting circuit that delivers a first detection signal to the error amplifier until the terminal voltage reaches a predetermined value and delivers a second detection signal to the error amplifier after the terminal voltage exceeds the predetermined value;
• and
• a logical product circuit that blocks output of the PWM signal in response to the first detection signal and allows output of the PWM signal in response to the second detection signal;
• wherein
• the error amplifier disables the amplification of the error between the output voltage and the target voltage for the output voltage in response to the first detection signal and enables the amplification of the error between the output voltage and the target voltage for the output voltage in response to the second detection signal.