Electric power conversion systems – Current conversion – Including automatic or integral protection means
Patent
1999-03-17
2000-08-08
Berhane, Adolf Deneke
Electric power conversion systems
Current conversion
Including automatic or integral protection means
363126, H02M 3335
Patent
active
06101107&
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a snubber circuit, a voltage converter circuit and a method in such a snubber circuit and specifically to a snubber circuit for connection across a coupling, element, a voltage converter circuit comprising such a snubber circuit and a method for reducing transient voltages present across such a coupling element. The invention is mainly meant for use in voltage converter circuits but is not limited to this field.
STATE OF THE ART
A snubber circuit usually comprises a capacitor in series with a resistor connected across a coupling element which can be influenced to conduct and not conduct current in order to reduce transient voltages across the coupling element.
WO-94/23488 discloses a number of snubber circuits in different converter circuits, where each snubber circuit is connected in parallel with a coupling element in the shape of a rectifier diode. These snubber circuits comprise a capacitor in series with a first diode in parallel with the coupling element. The snubber circuits also comprise a coil and a second diode. The object of such a snubber circuit is to ensure that the coupling element does not conduct in the reverse direction when switching occurs. The capacitor in this snubber circuit is mainly meant to handle energy from the coil.
U.S. Pat. No. 4,805,079 discloses a snubber circuit for limiting the voltage across a coupling element in the shape of a field effect transistor. The snubber circuit comprises two capacitors, a first being charged when the coupling element is released and the second simultaneously being discharged. When the coupling element is activated, the charged first capacitor is discharged.
DE-A1-4 421 249 discloses a snubber circuit with two serial circuits, each comprising a capacitor in series with a diode, the serial circuits being connected in parallel with one coupling element each. The serial circuits are also connected via a further serial circuit comprising a diode and a coil. These capacitors are charged and discharged in series, and the circuit is used in order to reduce losses when switching the coupling elements on and off, said coupling elements being connected to the primary side of a transformer, by dealing with the leakage inductance in the primary coil of the transformer.
DESCRIPTION OF THE INVENTION
The present invention addresses a problem of how to reduce transient voltages present across a coupling element, which arise when the coupling element is influenced to conduct.
A preferred embodiment of the invention addresses another problem of how to reduce leakage energy lost in a transformer when switching a voltage converter circuit.
An object of the present invention is thus to provide a method and a device reducing transient voltages present across a coupling element, which arise when the coupling element is influenced to conduct.
A further object of the present invention is to reduce leakage energy lost in a transformer in a voltage converter circuit when switching, so that the efficiency of the converter circuit is increased.
This is accomplished by charging at least two capacitors in series with a voltage applied across the coupling element when the coupling element is influenced not to conduct current, and discharging said capacitors in parallel when the coupling element is influenced to conduct so that the coupling element does not start to conduct until the capacitors are fully discharged.
This is accomplished with a snubber circuit for connection across the coupling element and a voltage converter circuit comprising such a coupling element and such a snubber circuit, the snubber circuit being connected in parallel with the coupling element and comprising a first serial circuit comprising a first capacitor and a first diode, and at least one second serial circuit connected in parallel with the first serial circuit and comprising a second capacitor and at least one second diode. All capacitors form a capacitive serial circuit in parallel with the coupling element, starting with the first capacito
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patent: 5923547 (1999-07-01), Mao
patent: 5982646 (1999-11-01), Lyson et al.
patent: 5986904 (1999-11-01), Jacobs et al.
Berhane Adolf Deneke
Telefonaktiebolaget LM Ericsson
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