Apparatus and efficiency point tracking method for high efficiency resonant converters
A system comprises an input power stage coupled to a primary side of a transformer, an output power stage coupled to a secondary side of a transformer, a first common node capacitor and a common node resistor connected in series between a midpoint of the secondary side of the transformer and ground and a detector having an input connected to a common node of the first common node capacitor and the common node resistor, and an output connected to a control circuit, wherein the control circuit is configured to dynamically adjust a switching frequency of the system based upon an output of the detector.
1. A system comprising:
a power converter configured to be coupled to a power source;
a detector coupled to a secondary side of a transformer of the power converter, wherein:
the detector is configured to detect a signal proportional to a current flowing through a first common mode capacitor directly connected to the transformer;
and
a control circuit configured as an adaptive control loop to dynamically adjust a switching frequency of the power converter based upon an output of the detector.
2. The system of claim 1 , wherein the power converter comprises an input stage and an output stage magnetically coupled to the input stage, and wherein the input stage comprises:
a plurality of power switches;
a resonant tank coupled to the plurality of power switches; and
a primary side of the transformer coupled to the resonant tank.
3. The system of claim 2 , wherein the output stage comprises:
the secondary side of the transformer magnetically coupled to the primary side of the transformer; and
a secondary rectifier coupled to the secondary side of the transformer.
4. The system of claim 1 , wherein:
the first common mode capacitor is directly connected to a midpoint of the secondary side of the transformer.
5. The system of claim 1 , wherein:
the first common mode capacitor is connected in series with a common mode resistor to form a common mode resistor-capacitor network.
6. The system of claim 5 , wherein:
an input of the detector is connected to a common node of the first common mode capacitor and the common mode resistor.
7. The system of claim 5 , further comprising:
a second common mode capacitor connected in parallel with the common mode resistor-capacitor network.
8. The system of claim 7 , wherein:
a capacitance value of the first common mode capacitor is equal to a capacitance value of the second common mode capacitor.
9. The system of claim 1 , wherein the detector comprises:
a dc blocking capacitor;
a rectifier coupled to the dc blocking capacitor, wherein the rectifier is configured to convert an ac signal into a dc signal;
and
a voltage divider coupled to the rectifier.
10. The system of claim 1 , wherein:
the control circuit configured to receive an efficiency point tracking signal from the detector and adjust a switching frequency of the power converter based upon the efficiency point tracking signal.
11. The system of claim 10 , wherein:
the control circuit is configured to adjust the switching frequency of the power converter so as to minimize the current flowing through a first common mode capacitor.
12. A method comprising:
detecting a signal indicating a soft switching process of an LLC resonant converter, wherein the signal is a current flowing through a first common mode capacitor directly connected to a transformer of the LLC resonant converter; and
adjusting a switching frequency of the LLC resonant converter by a control circuit based on the signal.
13. The method of claim 12 , further comprising:
adjusting the switching frequency of the LLC resonant converter until the current flowing through the first common mode capacitor is reduced.
14. The method of claim 12 , wherein:
the signal is detected at a common node of a first common mode capacitor and a common node resistor, and wherein the first common mode capacitor is coupled to a midpoint of a secondary winding of the transformer of the LLC resonant converter.
15. The method of claim 12 , further comprising:
feeding the signal into a detector circuit, wherein the detector circuit comprises a dc blocking capacitor, a signal rectifier, a divider and a filter, wherein the signal rectifier comprises a resistor and a diode, and wherein the dc blocking capacitor and the diode are connected in series, and the resistor is connected to a common node of the dc blocking capacitor and the diode.
16. The method of claim 12 , further comprising:
detecting the current flowing through the first common mode capacitor; and
configuring the switching frequency of the LLC resonant converter such that:
adjusting the switching frequency until the switching frequency is substantially equal to a resonant frequency of the LLC resonant converter.
17. A system comprising:
an input power stage coupled to a primary side of a transformer;
an output power stage coupled to a secondary side of a transformer;
a first common node capacitor and a common node resistor connected in series between a midpoint of the secondary side of the transformer and ground; and
a detector having an input connected to a common node of the first common node capacitor and the common node resistor, and an output connected to a control circuit, wherein the control circuit is configured to dynamically adjust a switching frequency of the system based upon an output of the detector.
18. The system of claim 17 , wherein the detector comprises:
a dc blocking capacitor;
a rectifier coupled to the dc blocking capacitor, wherein the rectifier is configured to convert an ac signal into a dc signal;
and
a voltage divider coupled to the rectifier.
19. The system of claim 17 , further comprising:
a second common mode capacitor connected in parallel with a common mode resistor-capacitor network formed by the first common node capacitor and the common node resistor.
20. The system of claim 17 , wherein:
the input power stage, the transformer and the output power stage form an LLC resonant converter.