Sub-resonant series resonant converter having improved form factor and reduced EMI
First Claim
1. A resonant converter for supplying current to a load circuit from a uni-polar source, including a resonant tank circuit coupled to said load circuit and comprising resonant tank elements defining a dominant resonant frequency of said tank circuit, and a bridge inverter circuit including alternately activated switching devices for supplying current from the source to the tank circuit, the improvement wherein:
- the switching devices of the bridge inverter circuit are activated at a switching frequency below said dominant resonant frequency of said tank circuit so that the current in said tank circuit includes a positive interval during which current is supplied to the tank circuit through an activated switching device followed by a negative interval during which the current in the tank circuit reverses through an anti-parallel diode shunting said activated switching device; and
said resonant tank elements include a tank inductor and tank capacitor connected in series, an additional capacitor connected in series with said tank capacitor and tank inductor, a boost inductor connected in parallel with said additional capacitor, the load also being connected in parallel with said additional capacitor, said additional capacitor operating to reduce the form factor of the current in said tank circuit while shortening said negative interval of such current so that the tank circuit current flowing in an anti-parallel diode shunting a given switching device is terminated, or nearly so, when the other switching device is activated.
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Accused Products
Abstract
An improved sub-resonant converter which retains the advantages generally associated with simple series resonant converters while additionally providing improved form factor and efficiency, and reducing EMI. The overall tank circuit includes at least a first inductor and first capacitor connected in series, a second capacitor connected in parallel with the load circuit, and a second inductor connected in parallel with the second capacitor for providing voltage boost capability. In addition to reducing dv/dt in the load circuit, the second capacitor draws a current that has the effect of reducing the form factor of the supplied current while shortening the negative portion of its cycle so that reverse current through the anti-parallel diode of one switching device is terminated, or nearly so, by the turn on of the next switching device, thereby reducing EMI associated with a rapid initial rise in current at such turn on. In a preferred embodiment, the tank circuit also includes a third inductor connected in parallel with the first capacitor to narrow the switching frequency range, thereby extending the above-described form factor and EMI improvements over the entire load range of the converter. In addition, the tank circuit is preferably coupled to the load circuit via an isolation transformer.
37 Citations
10 Claims
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1. A resonant converter for supplying current to a load circuit from a uni-polar source, including a resonant tank circuit coupled to said load circuit and comprising resonant tank elements defining a dominant resonant frequency of said tank circuit, and a bridge inverter circuit including alternately activated switching devices for supplying current from the source to the tank circuit, the improvement wherein:
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the switching devices of the bridge inverter circuit are activated at a switching frequency below said dominant resonant frequency of said tank circuit so that the current in said tank circuit includes a positive interval during which current is supplied to the tank circuit through an activated switching device followed by a negative interval during which the current in the tank circuit reverses through an anti-parallel diode shunting said activated switching device; and said resonant tank elements include a tank inductor and tank capacitor connected in series, an additional capacitor connected in series with said tank capacitor and tank inductor, a boost inductor connected in parallel with said additional capacitor, the load also being connected in parallel with said additional capacitor, said additional capacitor operating to reduce the form factor of the current in said tank circuit while shortening said negative interval of such current so that the tank circuit current flowing in an anti-parallel diode shunting a given switching device is terminated, or nearly so, when the other switching device is activated. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A resonant converter for supplying current to a load circuit from a uni-polar source, including a resonant tank circuit coupled to said load circuit and comprising resonant tank elements defining a dominant resonant frequency of said tank circuit, and a bridge inverter circuit including alternately activated switching devices for supplying current from the source to the tank circuit, the improvement wherein:
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the switching devices of the bridge inverter circuit are activated at a switching frequency below said dominant resonant frequency of said tank circuit so that the current in said tank circuit includes a positive interval during which current is supplied to the tank circuit through an activated switching device followed by a negative interval during which the current in the tank circuit reverses through an anti-parallel diode shunting said activated switching device; and said resonant tank elements include a tank inductor and tank capacitor connected in series, a second capacitor and second inductor connected in parallel with each other and in series with said tank inductor and tank capacitor, the load being connected in parallel with said second capacitor and second inductor, said second capacitor operating to reduce the form factor of the current in said tank circuit while shortening said negative interval of such current so that the tank circuit current flowing in an anti-parallel diode shunting a given switching device is terminated, or nearly so, when the other switching device is activated. - View Dependent Claims (8, 9, 10)
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Specification