Patent ID: 9735694
Date: 2017-08-15
CPC Classifications: H02M,Y02B

Claim:
1. A switching power-supply device that performs switching operation to control an output voltage, comprising: a first switching element; a transformer including a primary winding connected to the first switching element and a secondary winding magnetically coupled to the primary winding; a first control circuit configured to perform on-and-off control of the first switching element; a smoothing capacitor connected between a ground-side output terminal and a non-ground-side output terminal, where the ground-side output terminal is connected to one end of the secondary winding of the transformer and where the non-ground-side output terminal is connected to an other end of the secondary winding, of the switching power-supply device; an N-type transistor for rectification connected between the non-ground-side output terminal and the other end of the secondary winding; and a capacitor connected to a connection point of the N-type transistor and the other end of the secondary winding, an integrated circuit including: a second control circuit, which performs the on-and-off control of the N-type transistor by using a voltage of the capacitor as a power supply voltage; and a charging control circuit configured to control the charging circuit based on the voltage of the capacitor, wherein the charging circuit includes a diode, a second switching element, and a constant current circuit, where a first end of the diode is connected to the connection point or the ground-side output terminal and another end of the diode is connected to a first end of the second switching element, and the constant current circuit is connected between a second end of the second switching element and the capacitor, wherein the charging control circuit turns on the second switching element when the voltage of the capacitor is less than a first predetermined value and turns off the second switching element when the voltage of the capacitor reaches a second predetermined value, and wherein the charging circuit charges the capacitor during an on time period of the first switching element.