Switching power supply circuit

Abstract

A switching power supply circuit includes a switching element, a converter transformer, a secondary-side rectifying and smoothing circuit, a switching element control unit, a choke coil, a primary-side series resonant circuit, a primary-side parallel resonant circuit, and a series circuit. The switching element implements switching for a direct-current (DC) voltage to convert the voltage into an alternating-current (AC) voltage. The choke coil is supplied with the voltage and is connected to one winding end of the primary winding and one terminal of the switching element. The primary-side series resonant circuit connects a primary-side series resonant capacitor, having a resonant frequency dominated by a leakage inductance. The primary-side parallel resonant circuit connects a primary-side parallel resonant capacitor in parallel to the switching element, having a resonant frequency. The series circuit is formed of a clamp capacitor and an auxiliary switch element which conducts in a non-conducting period of the switching element.

Description

CROSS REFERENCES TO RELATED APPLICATIONS [0001] The present invention contains subject matter related to Japanese Patent Application JP 2005-287759 filed with the Japanese Patent Office on Sep. 30, 2005 and Japanese Patent Application JP 2005-291082 filed with the Japanese Patent Office on Oct. 4, 2005, the entire contents of which being incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a switching power supply circuit. [0004] 2. Description of the Related Art [0005] As types of a so-called soft switching power supply that employs a resonant converter, a current resonant type and a voltage resonant type have been widely known. Currently, half-bridge current resonant converters formed of a two-transistor switching element have been widely employed since they can easily be put into practical use. [0006] However, since characteristics of high-breakdown-voltage switching elements are currently being imp...

AI Technical Summary

Benefits of technology

[0042] Furthermore, power is supplied via the choke coil to one winding end of the primary winding in the converter transformer and one terminal of the switching element. Thus, the current supplied from the choke coil is a ripple current close to a DC current. In addition, by connecting the series resonant capacitor between the other winding end of the primary winding in the converter transformer and the other terminal of the switching element, the series resonant circuit of which resonant frequency is dominated by the leakage inductance arising in the primary winding in the converter transformer and the series resonant capacitor is formed. Moreover, the parallel resonant circuit of which resonant frequency is dominated by the primary-side parallel resonant capacitor connected in parallel to the switching element and the leakage inductance arising in the primary winding is formed. The formation of these resonant circuits can narrow the variable range of the switching frequency of the switching element.

[0045] In addition, a ripple current close to a DC current is obtained as the current flowing into the switching converter from the smoothing capacitor in the rectifying and smoothing circuit that produces the rectified and smoothed voltage (DC input voltage) from an AC power supply. Therefore, a small value can be assigned to the capacitance of the component element as the smoothing capacitor and the choice of a general-purpose product as the smoothing capacitor is allowed, which offers e.g. an advantage of reducing costs and size of the smoothing capacitor.

[0046] Moreover, as described above, reduction of power loss is achieved due to a decrease of the amount of the current flowing in the power supply circuit, and thus the total power conversion efficiency characteristic is greatly improved. Furthermore, a switching element of which breakdown voltage is low can be used.

Problems solved by technology

This waveform indicates abnormal operation in which ZVS is not implemented adequately.

That is, it is known that a voltage resonant converter including a secondary-side series resonant circuit as shown in FIG. 16 involves abnormal operation in which ZVS is not implemented adequately when the load is an intermediate load.

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