Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Patent
1997-09-29
1999-11-30
Riley, Shawa
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
363 56, 363 97, H02M 3335
Patent
active
059953853
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an RCC-type switching power supply, and more particularly to an RCC-type switching power supply having a snubber circuit which employs third-quadrant operation of a MOSFET device.
BACKGROUND ART
Electronic devices for producing a given DC voltage from a commercial AC power supply are called a stabilized power supply, and roughly classified into a dropper power supply and a switching power supply. The switching power supply is widely used in general as it is inexpensive and highly efficient.
One conventional switching power supply is denoted at 102 in FIG. 9. The switching power supply 102 comprises a flyback RCC(ringing choke converter)-type switching power supply, and has a diode bridge 120, a smoothing capacitor 121 on a primary side, a transformer 130, and a main switching means 106.
The transformer 130 comprises a primary winding 131, a secondary winding 132, and an auxiliary winding 133 which are arranged so as to be magnetically coupled.
The main switching means 106 comprises an NPN transistor having a collector terminal connected to an end of the primary winding 131. The diode bridge 120 and the smoothing capacitor 121 constitute a rectifying and smoothing means on the primary side for rectifying and smoothing an AC voltage having a commercial frequency and applying the rectified and smoothed voltage between the other end of the primary winding 131 and an emitter terminal of the main switching means 106. Therefore, when a current is supplied to a base terminal of the main switching means 106, rendering it conductive, the primary winding 131 is supplied with a current from the rectifying and smoothing means on the primary side.
The auxiliary winding 133 is connected between the base and emitter terminals of the main switching means 106. When a base current is supplied to render the main switching means 106 conductive and a current starts to flow through the primary winding 131, a voltage is induced across the auxiliary winding 133 for increasing the base current. Therefore, the current flowing through the primary winding 131 increases progressively from the time when the main switching means 106 starts being conductive.
The secondary winding 132 is connected to a rectifying and smoothing means on the secondary side which comprises a diode 135 and a smoothing capacitor. Because of the rectifying action of the diode 135, when the main switching means 106 is rendered conductive and a current flows through the primary winding 131, no current flows through the secondary winding 132, and when the main switching means 106 is cut off and the current flowing through the primary winding 131 stops, a current flows through the secondary winding 132.
FIG. 10 shows operating waveforms of the RCC-type switching power supply 102. The waveform indicated by the reference numeral 151 represents the current flowing through the primary winding 131, and the waveform indicated by the reference numeral 152 represents the current flowing through the secondary winding 132.
The waveform indicated by the reference numeral 153 represents the collector voltage of the main switching means 106, with a low level showing a conducted state thereof and a high level showing a cut-off state thereof. When the main switching means 106 changes from the conducted state to the cut-off state, the energy stored in the primary winding 131 is transferred to the secondary winding 132, causing a current to flow through the secondary winding 132.
The transfer of the energy from the primary winding 131 to the secondary winding 132 is carried out by a magnetic coupling between the primary winding 131 and the secondary winding 132. Since the magnetic coupling is actually not 100%, not all the energy of the primary winding 131 is transferred to the secondary winding 132. With the RCC-type switching power supply, in particular, a large gap is present in the core of the transformer 130, thus lowering the magnetic coupling between the primary winding 131 and the secondary winding 132 thereby increase the
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patent: 5383106 (1995-01-01), Yoshida et al.
patent: 5570278 (1996-10-01), Cross
Riley Shawa
Shindengen Electric Manufacturing Co. Ltd.
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