Shindengen Electric Manufacturing Company Limited

Matsushita Electric Industrial Co., Ltd.

Sony Corpotation

Haruo Watanabe

Yoshinori Kobayashi

Yutaka Sekine

Takuya Ishii

Kenji Kawasaki

Masanori Hayashi

Kenichi Suzuki

Satoshi Ikeda

Kenichi Kubota

Hiroyuki Haga

Yoshihiko Kikuchi

Yoshio Mizutani

Kenji Horiguchi

Yukihiro Nozaki

Haruhiko Hatakeyama

Takeshi Karii

Yoichi Okada

Masaki Oshima

Kenichi Zenta

A switching power supply; wherein a voltage detector is provided at the output of a power supply circuit and connected to the negative input of an error amplifier to amplify the error between detected voltage and reference voltage, the output of said amplifier is connected to the negative input of a first comparator and to the negative input of a second comparator through split resistors, a filter circuit is connected between a control switch and synchronous switch and the output of said filter circuit is connected to a first comparator and a second comparator, wherein said configuration constitues a control means to control the amplitude of the triangular waveform obtained through said filter circuit to be between an input level of said first comparator and an input of said second comparator, whereby the stability of the switching power supply is ensured without lowering the frequency band of said amplified error signal and stable output ripple characteristics can be materialized.

Switching power supply

A switching power supply has first and second switching elements that are alternately turned on to cause an alternating current to flow through a primary winding of a transformer. The alternating current flowing through the primary winding induces voltages respectively across first and second secondary windings of the transformer. Synchronous rectifying transistors are turned on by the voltages induced across the first and second secondary windings, causing a current to flow alternately through the first and second secondary windings. Either one of the first and second switching elements is turned on while the other is being turned off, except for short off-times in which both the first and second switching elements are prevented from being turned on. As a result, when currents flow through the first and second secondary windings, the synchronous rectifying transistors are turned on. Therefore, no current flows through internal parasitic diodes of the synchronous rectifying transistors, and hence any loss caused thereby is very small.

In a driving pulse output limiting circuit, ideal switching operations are performed in all oscillation permitting frequencies and in all impedance conditions free from excessive surge current stresses due to excessive driving pulse width. While a charging current or a discharging current is being supplied to a capacity 11 which is connected between both ends of a switching element 3 or between windings of a main transformer 7, voltages are generated between both ends of a switching element 2 and between both ends of the switching element 3. A pulse voltage which is generated accordingly between both ends of an impedance element 13 connected in series to the capacity 11 is detected with a charging current detecting circuit 32 or a discharging current detecting circuit 35, and outputs of these circuits are applied to pulse limiting circuits 30 and 31 for blocking driving input signals to the driving circuit of switching elements 2 and 3, thereby limiting driving pulses to the switching elements so that these elements are driven after the pulse voltages applied between both ends thereof are lowered to about 0�V!.

Driving pulse output limiting circuit

An AC-DC converter which allows an input current of an input AC power source to have harmonic currents of reduced levels and which supplies a stabilized output DC voltage to a load is realized by a simple circuit configuration. The converter has: a converter circuit consisting of a choke coil which receives a rectified voltage from a rectifying circuit, a switch element, and a diode; a smoothing capacitor which smooths the output voltage of the converter circuit and supplies the smoothed voltage to a load; and a control circuit consisting of a current detection circuit, a voltage detection circuit, and a pulse-width control circuit. In order to stabilize the output voltage, the switch element is turned on and off so that the peak value of the input current of the converter circuit is limited in a DC-like manner, thereby allowing the input current to have a trapezoidal waveform.

AC-DC converter

Growing community of inventors

Saitama, Japan

Haruo Watanabe