Electric power conversion systems – Current conversion – Including automatic or integral protection means
Patent
1995-07-12
1998-04-28
Sterrett, Jeffrey L.
Electric power conversion systems
Current conversion
Including automatic or integral protection means
363 19, 363131, H02H 7122
Patent
active
057453535
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a snubber circuit, a switching power source, and a saturable inductor for use therein.
BACKGROUND ART
Heretofore, bipolar transistors have been mainly used as switching elements for switching power sources. In recent years, the demands for diminishing sizes and weights of switching power sources have been urging an increase in the operating frequency of such switching power sources. As a measure for this increase, the use of field effect transistors (hereinafter referred to as "FET") has been in vogue.
High-speed switching is realized when a FET is used as a switching element as described above. Since an electric current suddenly flows into a gate capacity (hereinafter referred to as "rush current") while the FET is ON, however, there arises the problem of an increased loss due to the emission of noise from the FET or the instantaneous increase of the electric current flowing to the FET. To solve this problem, measures such as parallelly connecting a snubber circuit, such as a CR snubber consisting of a capacitor C and a resistor R, to the FET thereby depriving the voltage of oscillation by absorption and preventing the electric current from producing a sudden change, are adopted.
Not exclusively in the case of using a FET, the practice of parallelly connecting to a switching element a snubber circuit such as a snubber capacitor in the switching power source is prevailing. It serves to prevent the voltage from suddenly rising at the moment that the switching element is turned off and, at the same time, repress the surge voltage which is emitted by the leakage inductance of a transformer. By these measures, the switching element is protected and, at the same time, the external leakage of noise is diminished.
FIG. 7 illustrates one example of the circuit of the conventional flyback type switching power source which is adapted to use the self-oscillation of a blocking oscillator. In the flyback type switching power source shown in this diagram, a primary winding 4 of a transformer 3 and a FET 5 are connected in series between input terminals 1 and 2 and the transformer 3 is provided with a winding 6 for actuating the gate circuit of the FET 5. Between the gate circuit of the FET 5 and the winding 6 for driving the FET, a resistor 8 for optimizing the electric current level and a capacitor 7 for improving the operating characteristics are connected in series. Between the primary winding 4 of the transformer 3 and the input terminal 2, a snubber capacitor 9 and a snubber resistor 10 are connected in parallel to the FET 5 to protect the FET 5.
To a secondary winding 11 of the transformer 3 is connected a rectifying element 12. Outlet terminals 13 and 14 are also connected to the secondary winding 11. A capacitor 15 which is connected in parallel between the output terminals 13 and 14 is adapted to smooth the output in conjunction with the rectifying element 12. A resistor 16 is a load.
Incidentally, in the switching power source constructed as described above, such snubber circuits as the CR snubbers (9, 10) must be given an increased size in order to preclude emission of noise. The increased size inevitably adds to the loss due to the snubber circuits and the loss ironically poses itself a problem. It further entails the problem that when the switching element is turned on, the energy of the CR snubbers flows into the switching elements and functions therein as a surge current to bring about emission of noise and degradation of efficiency.
Particularly, in the flyback type switching power source using self-oscillation, the primary inductance component of the transformer and the capacity such as of the capacitors of the snubber circuits jointly generate resonance during the interval of shift from the ON period to the OFF period. The resonance entails the problem that the switching element is actuated during the resonance, depending on the capacity, and the energy accumulated in the capacity, such as the capacitors of the snubber circuits, flows into the switching ele
REFERENCES:
patent: 4031453 (1977-06-01), Teuling
patent: 4353113 (1982-10-01), Billing
patent: 4510562 (1985-04-01), Maeba
patent: 4888672 (1989-12-01), Hiramatsu et al.
patent: 5499175 (1996-03-01), Noro
patent: 5515256 (1996-05-01), Yokoyama
Kusaka Takao
Momose Kenichiro
Saito Tadao
Sato Morio
Kabushiki Kaisha Toshiba
Sterrett Jeffrey L.
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