Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Patent
1999-07-21
2000-12-05
Riley, Shawn
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
323300, 323290, G05F 144
Patent
active
061571814
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a step-down DC/DC converter, and more particularly to a step-down DC/DC converter for converting a high DC input voltage into a low DC output voltage.
BACKGROUND ART
Heretofore, there have been widely used step-down DC/DC converters in power supply circuits for electronic devices or the like, for turning on and off semiconductor switching elements to convert a DC input power supply voltage into a DC output voltage which is lower than the DC input power supply voltage.
FIG. 1 is a circuit diagram of the arrangement of a conventional step-down DC/DC converter.
As shown in FIG. 1, the conventional step-down DC/DC converter comprises a DC power supply 101, a main transistor 102 as a main switching element having a collector terminal connected to the positive terminal of the DC power supply 101, a main recirculation diode 103 as a main recirculation rectifying element connected between the emitter terminal of the main transistor 102 and the negative terminal of the DC power supply 101, with the emitter terminal of the main transistor 102 being connected to the cathode of the main recirculation diode 103, a series-connected circuit comprising a smoothing reactor 104 and a smoothing capacitor 105 which are connected parallel to the main recirculation diode 103, a load 106 connected parallel to the smoothing capacitor 105, and a control circuit 107 for outputting an on and off control signal to the base terminal of the main transistor 102.
In the step-down DC/DC converter of the above arrangement, depending on a change in the voltage across the smoothing capacitor 105, which is a low DC output voltage, the duration of the on and off control signal applied to the base terminal of the main transistor 102 varies for thereby controlling the on period of the main transistor 102 to stabilize the voltage across the smoothing capacitor 105, i.e., the voltage supplied to the load 106.
FIG. 2 is a diagram showing an overlap between a switching voltage waveform and a switching current waveform of the step-down DC/DC converter shown in FIG. 1.
As shown in FIG. 2, the step-down DC/DC converter shown in FIG. 1 has a problem in that when the main transistor 102 is turned on or off, a collector-to-emitter voltage waveform V.sub.CE of the main transistor 102 and a collector current waveform Ic of the main transistor 102 overlap each other in areas W, and a large switching loss occurs in the overlapping areas W. Another problem is that spike surge voltage V.sub.SR, surge current I.sub.SR, and noise are produced at positive-going edges of the collector-to-emitter voltage waveform V.sub.CE and the collector current waveform I.sub.C.
Japanese laid-open patent publication No. 7-241071 discloses a step-down DC/DC converter capable of reducing the switching loss, the surge voltage, the surge current, etc. as described above.
FIG. 3 is a circuit diagram showing the arrangement of the step-down DC/DC converter disclosed in Japanese laid-open patent publication No. 7-241071.
As shown in FIG. 3, the step-down DC/DC converter disclosed in Japanese laid-open patent publication No. 7-241071 includes, as parts added to the step-down DC/DC converter shown in FIG. 1, a series-connected circuit of an auxiliary transistor 109 as an auxiliary switching element and a resonant reactor 110 which are connected parallel to the main transistor 102, a series-connected circuit of auxiliary recirculation diodes 111, 112 connected between the junction between the auxiliary transistor 109 and the resonant reactor 110 and the negative terminal of the DC power supply 101, a resonant capacitor 108 connected between the junction between the auxiliary recirculation diodes 111, 112 and the emitter terminal of the main transistor 102, and a circulating current diode 113 connected parallel to the main transistor 102.
Operation of the step-down DC/DC converter of the above arrangement will be described below.
When the main transistor 102 is turned off while a current is flowing to the load 106 and the resonant capacit
REFERENCES:
patent: 5610503 (1997-03-01), Fogg et al.
Kabushiki Kaisha Yaskawa Denki
Riley Shawn
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