Patent ID: 7948780
Filing Date: 2011-05-24
Classification: H02M

Abstract:
1. A semiconductor device for switching power supply control in a switching power supply device which has a DC power supply, a transformer, a switching element connected to the DC power supply to control a current flowing in a primary-side main winding of the transformer, and a capacitor for voltage stabilization connected to an auxiliary winding of the transformer, and which supplies power to a load connected to a secondary-side winding of the transformer, comprising: a high-voltage input terminal for startup, connected to the DC power supply; a power supply terminal, which is connected to the capacitor for voltage stabilization, and which outputs a startup current to charge the capacitor for voltage stabilization after power supply input to the switching power supply device; and a startup circuit, which is connected between the high-voltage input terminal and the power supply terminal, and which charges the capacitor while controlling the startup current at a magnitude corresponding to a voltage value of the power supply terminal, and turns off the startup current after startup of the switching power supply device and supplies a power supply voltage from the transformer auxiliary winding to the power supply terminal wherein the startup circuit has a startup device connected to the high-voltage input terminal, a voltage-current conversion circuit which generates a first variable current signal of magnitude corresponding to a voltage signal at the power supply terminal, and a current amplification circuit, provided between the startup device and the power supply terminal, for generating a second variable current signal serving as the startup current, based on the first variable current signal.