Adjustable resonant apparatus for power converters
An apparatus comprises a first series resonant inductor coupled to a switching network and a transformer, a first series resonant capacitor coupled to the switching network and the transformer, a first parallel inductor coupled to the switching network through the first series resonant inductor and the first series resonant capacitor, a resonant frequency adjusting device coupled to the switching network and the transformer and a switch connected in series with the resonant frequency adjusting device.
1. An apparatus comprising:
a first series resonant inductor coupled to a switching network and a transformer;
a first series resonant capacitor coupled to the switching network and the transformer;
a first parallel inductor coupled to the switching network through the first series resonant inductor and the first series resonant capacitor;
a resonant frequency adjusting device coupled to the switching network and the transformer; and
a switch connected in series with the resonant frequency adjusting device, wherein the switch is formed by two back-to-back connected transistors, and wherein the switch has a first terminal directly connected with the resonant frequency adjusting device and a second terminal directly connected with the switching network, and wherein the switch comprises a first transistor and a second transistor that are turned off when a load of the apparatus is greater than a predetermined threshold and turned on when the load of the apparatus is less than the predetermined threshold.
2. The apparatus of claim 1 , wherein:
the resonant frequency adjusting device is a capacitor.
3. The apparatus of claim 2 , wherein:
the switch and the capacitor form a second series resonant capacitor; and
the second series resonant capacitor and the first series resonant capacitor are connected in parallel.
4. The apparatus of claim 1 , wherein:
the resonant frequency adjusting device is an inductor.
5. The apparatus of claim 4 , wherein:
the switch and the inductor form a second series resonant inductor; and
the second series resonant inductor and the first series resonant inductor are connected in parallel.
6. The apparatus of claim 1 , wherein:
the first parallel inductor is implemented as a magnetizing inductance of the transformer.
7. The apparatus of claim 1 , wherein:
the first parallel inductor is implemented as a separate inductor coupled between a primary side winding of the transformer.
8. A system comprising:
an input power source;
a switching network comprising:
a first pair of switches coupled between the input power source; and
a second pair of switches coupled between the input power source;
a resonant tank connected between the switching network and a primary side of a transformer, wherein the resonant tank comprises:
a first series resonant inductor coupled to the switching network and the transformer;
a first series resonant capacitor coupled to the switching network and the transformer;
a first parallel inductor coupled to the switching network through the first series resonant inductor and the first series resonant capacitor;
a resonant frequency adjusting device coupled to the switching network and the transformer; and
a switch connected in series with the resonant frequency adjusting device, wherein the switch has a first terminal directly connected with the resonant frequency adjusting device and a second terminal directly connected with a common node of the switches of the switching network, and wherein the switch comprises a first transistor and a second transistor back-to-back connected, and wherein the first transistor and the second transistor are configured such that:
both the first transistor and the second transistor are turned off when a load of the system is greater than a predetermined threshold; and
at least one transistor of the first transistor and the second transistor is turned on when the load of the system is less than the predetermined threshold;
a rectifier coupled to a secondary side of the transformer; and
an output filter coupled to the rectifier.
9. The system of claim 8 , wherein:
the switching network, the resonant tank, the transformer, the rectifier and the output filter form an LLC resonant converter.
10. The system of claim 9 , wherein the switch is configured such that:
the LLC resonant converter is of a first resonant frequency when the switch is turned on; and
the LLC resonant converter is of a second resonant frequency when the switch is turned off.
11. The system of claim 8 , wherein:
the switch is formed by two back-to-back connected metal oxide semiconductor transistors.
12. The system of claim 8 , wherein:
the transformer is a center-tapped transformer; and
the rectifier is a synchronous rectifier.
13. The system of claim 8 , wherein:
the transformer is a non center-tapped transformer; and
the rectifier is a full-wave rectifier.
14. A method comprising:
providing a resonant tank coupled between a switching network and a transformer, wherein the resonant tank comprises:
a first series resonant inductor coupled to a switching network and the transformer;
a first series resonant capacitor coupled to the switching network and the transformer;
a first parallel inductor coupled to the switching network through the first series resonant inductor and the first series resonant capacitor;
a resonant frequency adjusting device coupled to the switching network and the transformer; and
a switch connected in series with the resonant frequency adjusting device, wherein the switch comprises a first transistor and a second transistor back-to-back connected in series;
in response to a load increase, turning off both the first transistor and the second transistor and configuring the switching network to operate at a first switching frequency approximately equal to a first resonant frequency; and
in response to a load drop, turning on the first transistor, keeping the second transistor off and configuring the switching network to operate at a second switching frequency approximately equal to a second resonant frequency.
15. The method of claim 14 , further comprising:
detecting a load current flowing through the switching network;
comparing the load current with a predetermined load threshold;
turning on the switch when the load current is less than the predetermined load threshold; and
turning off the switch when the load current is greater than the predetermined load threshold.
16. The method of claim 15 , wherein:
the predetermined load threshold is about 50% of a full load of the switching network.
17. The method of claim 14 , wherein:
the resonant frequency adjusting device is a capacitor, wherein the capacitor and the first series resonant capacitor are connected in parallel through the switch.
18. The method of claim 14 , further comprising:
coupling the switching network to a dc input power source;
coupling a primary side of a converter and a secondary side of the converter through the transformer providing isolation between the primary side and the secondary side of the converter;
coupling a rectifier to the secondary side; and
coupling an output filter to the rectifier.