Switch mode power converter
A switch mode power converter comprises an inverter, a transformer having a primary side winding and a secondary side winding and a first inductor in series with the primary side winding. A second inductor is provided magnetically coupled to the first inductor, and a voltage at one end of the second inductor is used as a feedback signal for indirectly measuring (i.e. approximating) the secondary side voltage, but with measurement at the primary side.
1. A switch mode power converter, comprising:
an inverter comprising a high side switch and a low side switch connected in series with a first node between the high side switch and the low side switch;
a transformer having a primary side winding and a secondary side winding; and
a first inductor in series with the primary side winding and connected to the primary side winding at a second node;
a second inductor magnetically coupled to the first inductor, the second inductor defining an first end coupled to the primary side winding and an output terminal at a second end counted to a controller; and
wherein the controller for controlling the inverter, wherein the controller has an input for receiving a signal derived from the voltage at the output terminal,
wherein the second inductor has an inductance approximately equal to or greater than a combined primary side series leakage inductance of the transformer.
2. The converter as claimed in claim 1 , further comprising a series capacitor in series with the first inductor and a capacitor in parallel with the secondary side winding.
3. The converter as claimed in claim 1 , wherein the controller has an input directly connected to the output terminal.
4. The converter as claimed in claim 1 , wherein the controller has a combining circuit for combining signals at the second node and at the output terminal to derive a sensing signal which is provided to the controller.
5. The converter as claimed in claim 4 , wherein the combining circuit comprises a resistor network-for combining voltages at the second node and the output terminal to provide a sensing signal voltage.
6. The converter as claimed in claim 4 , wherein the combining circuit comprises a circuit for generating a sensing signal current.
7. The converter as claimed in claim 1 , wherein the second inductor has a first end connected to the second node and the output terminal at a second end.
8. The converter as claimed in claim 1 , wherein the second inductor has a first end connected to ground and the output terminal at a second end.
9. The converter as claimed in claim 1 , comprising a resonant converter with a resonant tank connected to the first node, the resonant tank comprising the first inductor.
10. The converter as claimed in claims 1 , further comprising a rectifier connected to the secondary side winding, and a storage capacitor across the rectifier output.
11. The converter as claimed in claim 10 , wherein the rectifier comprises a four-diode bridge connected across the secondary side winding.
12. The converter as claimed in claim 10 , wherein the transformer has first and second secondary side windings in series, with a node defined between the second secondary windings in series, wherein the rectifier comprises a two diode arrangement.
13. A lighting circuit comprising:
the converter as claimed in claim 10 , and
a lighting load in parallel with the storage capacitor.