Power supply circuit

摘要

A power supply circuit (1) including: rectifying and smoothing circuit (31); transistor (switching element) (37) connected to an output terminal of the rectifying and smoothing circuit (31); transformer (TF1) including primary coil (L36) connected to the transistor (37) and secondary coil (L47) magnetically coupled with the primary coil (L36); current detector circuit (41) detecting current flowing through the transistor (37), and outputting voltage corresponding to the current; voltage output circuit (44) outputting, while the transistor (37) is in a turned-on state, voltage dependent on voltage induced by the secondary coil (L47); and on-off control circuit (57) turning off the transistor (37) when absolute value (Vbe) of a difference between the voltage from the current detector circuit (41) and the voltage from the voltage output circuit (44) is no smaller than threshold voltage (Von), and turning on the transistor (37) when the absolute value (Vbe) is smaller than the threshold voltage (Von).

主权项

1. A power supply circuit comprising:
a DC power supply; a switching element disposed in a current path extending from an output terminal at a high-potential side of the DC power supply to an output terminal at a low-potential side of the DC power supply, via a load; a transformer including a primary coil disposed in the current path and a secondary coil magnetically coupled with the primary coil; a current detector circuit detecting current flowing through the switching element, and outputting voltage corresponding to the current thus detected; a voltage output circuit outputting, when the switching element is turned on, voltage that is dependent on voltage induced by the secondary coil; and an on-off control circuit turning off the switching element when an absolute value of a difference between the voltage output by the current detector circuit and the voltage output by the voltage output circuit is equal to or greater than a threshold voltage, and turning on the switching element when the absolute value of the difference is smaller than the threshold voltage.