Three-level zeta asymmetrical half-bridge

1 . A three-level zeta asymmetrical half-bridge for converting a direct current (DC) input voltage into a DC output voltage comprising:

an asymmetrical half-bridge comprising a first pair of switching elements and a second pair of switching elements in series with the first pair of switching elements;

a resonant tank in parallel with one switching element from each pair of switching elements, the resonant tank comprising a magnetizing inductance of a primary winding of a transformer, a resonant inductance, and a primary resonant capacitance; and

a zeta converter connected to a secondary winding of the transformer;

wherein the three-level zeta asymmetrical half-bridge is configured to apply a first portion of the DC input voltage in parallel with the first pair of switching elements and to apply a second portion of the DC input voltage in parallel with the second pair of switching elements;

wherein each pair of switching elements is configured to operate in a sequence to selectively connect and disconnect the resonant tank to and from the respective first or second portion of the DC input voltage such that a voltage applied to the resonant tank alternates between a lower voltage and a higher voltage;

wherein the resonant tank is configured to filter out a DC component of the voltage applied to the resonant tank and output a filtered resonant tank voltage to the primary winding of the transformer;

wherein the first pair of switching elements and the second pair of switching elements are configured to operate in different modes so as to:

in a first mode, alternate the voltage applied to the resonant tank between half the DC input voltage and ground; and

in a second mode, alternate the voltage applied to the resonant tank between the DC input voltage and half the DC input voltage; and

wherein the zeta converter is configured to rectify an output of the secondary winding of the transformer to generate the DC output voltage.

2 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein each of the switching elements comprises a switch, a diode, and a capacitance in parallel.

3 . The three-level zeta asymmetrical half-bridge of claim 2 , wherein each of the switching elements is configured to switch on when a voltage across the respective switching element is zero.

4 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein the zeta converter comprises:

a secondary resonant capacitance in series with the secondary winding of the transformer;

a rectifying diode in series with the secondary winding of the transformer;

an output inductor in series with the secondary resonant capacitance and in parallel with the rectifying diode; and

an output capacitor in series with the output inductor; and

wherein the three-level zeta asymmetrical half-bridge is configured to apply the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor.

5 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein the zeta converter comprises:

a rectifying switching element comprising a switch and a diode in parallel, wherein the rectifying switching element is in series with the secondary winding of the transformer;

an output inductor in parallel with the rectifying switching element; and

an output capacitor in series with the output inductor; and

wherein the three-level zeta asymmetrical half-bridge is configured to apply the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor.

6 . The three-level zeta asymmetrical half-bridge of claim 5 , wherein the rectifying switching element is a metal-oxide semiconductor field effect transistor (MOSFET) with an integrated body diode and switch.

7 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein:

the transformer is a tapped transformer;

the zeta converter comprises:

a rectifying diode in series with the secondary winding of the transformer;

an output inductor connected part-way along the secondary winding of the transformer; and

an output capacitor in series with the output inductor;

the three-level zeta asymmetrical half-bridge is configured to apply the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor; and

the zeta converter further comprises a secondary resonant capacitance in series with each of the secondary winding of the transformer, the rectifying diode, and the output inductor.

8 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein:

the transformer is a tapped transformer;

the zeta converter comprises:

a rectifying switching element comprising a switch and a diode in parallel, wherein the rectifying switching element is in series with the secondary winding of the transformer;

an output inductor connected part-way along the secondary winding of the transformer; and

an output capacitor in series with the output inductor;

the three-level zeta asymmetrical half-bridge is configured to apply the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor; and

the zeta converter further comprises a secondary resonant capacitance in series with each of the secondary winding of the transformer, the rectifying switching element, and the output inductor.

9 . The three-level zeta asymmetrical half-bridge of claim 8 , wherein the rectifying switching element is a metal-oxide semiconductor field effect transistor (MOSFET) with an integrated body diode and switch.

10 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein the resonant inductance is a leakage inductance of the primary winding of the transformer.

11 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein the switching elements are configured to alternate the voltage applied to the resonant tank between the lower voltage and the higher voltage at a fixed frequency.

12 . The three-level zeta asymmetrical half-bridge of claim 11 , wherein a proportion of time that the voltage applied to the resonant tank is the higher voltage is varied.

13 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein the switching elements are configured to operate to generate a square wave to the resonant tank such that the voltage applied to the resonant tank is a square wave.

14 . The three-level zeta asymmetrical half-bridge of claim 1 , wherein:

the DC input voltage is split across a first capacitor, across which the first portion of the DC input voltage is applied, and a second capacitor, across which the second portion of the DC input voltage is applied; and

the first capacitor is in series with the second capacitor.

15 . A method of operating a three-level zeta asymmetrical half-bridge to convert a direct current (DC) input voltage into a DC output voltage, wherein the three-level zeta asymmetrical half-bridge comprises:

an asymmetrical half-bridge comprising a first pair of switching elements and a second pair of switching elements in series with the first pair of switching elements;

a resonant tank in parallel with one switching element from each pair of switching elements, the resonant tank comprising a magnetizing inductance of a primary winding of a transformer, a resonant inductance, and a primary resonant capacitance; and

a zeta converter connected to a secondary winding of the transformer;

the method comprising:

applying a first portion of the DC input voltage in parallel with the first pair of switching elements;

applying a second portion of the DC input voltage in parallel with the second pair of switching elements;

operating each pair of switching elements in a sequence to selectively connect and disconnect the resonant tank to and from the respective first or second portion of the DC input voltage such that a voltage applied to the resonant tank alternates between a lower voltage and a higher voltage;

using the resonant tank, filtering out a DC component of the voltage applied to the resonant tank and outputting a filtered resonant tank voltage to the primary winding of the transformer; and

using the zeta converter, rectifying an output of the secondary winding of the transformer to generate the DC output voltage;

wherein the first pair of switching elements and the second pair of switching elements operate in different modes so as to:

in a first mode, alternate the voltage applied to the resonant tank between half the DC input voltage and ground; and

in a second mode, alternate the voltage applied to the resonant tank between the DC input voltage and half the DC input voltage.

16 . The method of claim 15 , wherein the zeta converter comprises:

a secondary resonant capacitance in series with the secondary winding of the transformer;

a rectifying diode in series with the secondary winding of the transformer;

an output inductor in series with the secondary resonant capacitance and in parallel with the rectifying diode; and

an output capacitor in series with the output inductor; and

wherein the three-level zeta asymmetrical half-bridge applies the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor.

17 . The method of claim 15 , wherein the zeta converter comprises:

a rectifying switching element comprising a switch and a diode in parallel, wherein the rectifying switching element is in series with the secondary winding of the transformer;

an output inductor in parallel with the rectifying switching element; and

an output capacitor in series with the output inductor; and

wherein the three-level zeta asymmetrical half-bridge applies the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor.

18 . The method of claim 15 , wherein:

the transformer is a tapped transformer;

the zeta converter comprises:

a rectifying diode in series with the secondary winding of the transformer;

an output inductor connected part-way along the secondary winding of the transformer; and

an output capacitor in series with the output inductor;

the three-level zeta asymmetrical half-bridge applies the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor; and

the zeta converter further comprises a secondary resonant capacitance in series with each of the secondary winding of the transformer, the rectifying diode, and the output inductor.

19 . The method of claim 15 , wherein:

the transformer is a tapped transformer;

the zeta converter comprises:

a rectifying switching element comprising a switch and a diode in parallel, wherein the rectifying switching element is in series with the secondary winding of the transformer;

an output inductor connected part-way along the secondary winding of the transformer; and

an output capacitor in series with the output inductor;

the three-level zeta asymmetrical half-bridge applies the DC output voltage to a load in parallel with the output capacitor and in series with the output inductor; and

the zeta converter further comprises a secondary resonant capacitance in series with each of the secondary winding of the transformer, the rectifying switching element, and the output inductor.

20 . The method of claim 15 , wherein the voltage applied to the resonant tank is a square wave.