Resonant converter
Consistent with an example embodiment, a resonant converter comprises a signalling transformer that is used to transfer information between the secondary winding and primary winding of the converter whilst maintaining mains isolation between the two sides. In the embodiment, according to the disclosure, the use of a signalling transformer (in addition to a switching, or resonant, transformer) eliminates the need for an opto-coupler to transfer information and so allows for the construction of a simpler, more reliable and/or cheaper resonant converter. Other embodiments described herein may be suitable for use in dimmable LED driver applications, for example.
1. A resonant converter having a primary side for receiving a DC voltage from an input power supply and a secondary side for providing a DC output voltage, the resonant converter comprising:
a first converter switch;
a second converter switch coupled in series with the first converter switch, wherein the first and second converter switches are provided across the input power supply;
a switching transformer with a primary side winding and a secondary side winding, wherein the primary side winding is coupled in parallel with the second converter switch, the switching transformer configured to transfer energy from the primary side winding to the secondary side winding of the switching transformer;
a resonant tank associated with the primary side winding of the switching transformer;
a signalling transformer with a primary side winding and a secondary side winding, wherein the secondary side winding of the signalling transformer is connected to the secondary side winding of the switching transformer and configured to transfer a signal from the secondary side winding of the signalling transformer to the primary side winding of the signalling transformer; and
a primary side controller configured to control the first and second converter switches in response to the signal received at the primary side winding of the signalling transformer,
wherein the switching transformer has a first secondary side winding and a second secondary side winding and the signalling transformer has a first secondary side winding and a second secondary side winding,
wherein a first terminal of the first secondary side winding of the switching transformer is coupled to a first terminal of the second secondary side winding of the switching transformer and to ground, a second terminal of the first secondary side winding of the switching transformer is coupled to a first terminal of the first secondary side winding of the signalling transformer, a second terminal of the second secondary side winding of the switching transformer is coupled to a first terminal of the second secondary side winding of the signalling transformer.
2. The resonant converter of claim 1 , wherein the primary and secondary windings of the signalling transformer have a substantially lower inductance than the primary and secondary windings of the switching transformer.
3. The resonant converter of claim 2 , wherein the inductance of the signalling transformer is 3 orders of magnitude lower than the inductance of the switching transformer.
4. The resonant converter of claim 1 , wherein the signalling transformer is substantially isolated from a magnetic field generated by the switching transformer.
5. The resonant converter of claim 1 , wherein the primary side controller is configured to control the first and second converter switches in order to provide a constant current at the output power supply.
6. The resonant converter of claim 1 , wherein the secondary side winding of the signalling transformer is coupled in series with the secondary side winding of the switching transformer.
7. The resonant converter of claim 6 , wherein the secondary side winding of the signalling transformer is coupled in parallel with a sense resistor.
8. A light emitting diode, LED, driver circuit comprising the resonant converter of claim 1 .
9. The resonant converter of claim 1 , wherein a second terminal of the first secondary side winding of the signalling transformer is coupled to a load terminal and a second terminal of the second secondary side winding of the signalling transformer is coupled to the load terminal.
10. The resonant converter of claim 9 , wherein the load terminal is respectively coupled to the first and second secondary side windings of the signalling transformer by first and second rectifiers and wherein the polarity of the first rectifier is the same as the polarity of the second rectifier.
11. The resonant converter of claim 10 , wherein at least one of the first and second rectifiers is a synchronous rectifier.
12. The resonant converter of claim 1 , wherein the signalling transformer further comprises an additional secondary side winding, the resonant converter further comprising a secondary side controller that is configured to control a flow of energy through the additional secondary side winding in response to receiving a control signal or in response to a current in the secondary side of the resonant converter.
13. The resonant converter of claim 12 , wherein the secondary side controller is configured to short circuit the additional secondary side winding in response to receiving the control signal or in response to a current in the secondary side of the resonant converter.
14. The resonant converter of claim 12 , wherein the secondary side controller is configured to receive the command as a user input.