Half-bridge isolation stage topologies
Half-bridge isolation stage topologies are provided in power converters, dividing an input voltage between capacitors. Primary transformer windings are periodically switched across respective capacitors. In current-fed implementations, the current flow through the primary windings is constrained as by an inductive element. In some implementations, a capacitor, primary winding and switch are connected in series in different orders in each of plural legs across the input. Current feed circuitry includes a current constraining component connecting nodes within each of respective legs. The switches of the isolation stage may be turned on with a fixed duty cycle, and a secondary circuit may comprise synchronous rectifiers.
1. A current fed DC to DC power converter comprising:
a primary circuit comprising:
an input which receives an input voltage and an input current from a DC source;
capacitors connected across the input and dividing the input voltage therebetween;
transformer primary windings;
switches which periodically switch the primary windings across respective capacitors; and
current feed circuitry including a magnetic element distinct from the transformer primary windings and having DC current flow therethrough that constrains current flow through each primary winding as current flows through the winding; and
a secondary circuit driven by the primary windings to provide a DC output, current flowing through a secondary winding as current flows through a respective primary winding.
2. A converter as claimed in claim 1 comprising two capacitors connected across the input, each capacitor charging to about one-half the input voltage.
3. A converter as claimed in claim 2 wherein each of the switches conducts about twice the input current.
4. A converter as claimed in claim 1 wherein transformer secondary windings of the secondary circuit are not tightly coupled.
5. A converter as claimed in claim 4 wherein first and second pairs of primary and secondary windings are provided on separate transformers.
6. A converter as claimed in claim 1 wherein the magnetic element is an inductor.
7. A converter as claimed in claim 1 wherein the magnetic element is a transformer.
8. A converter as claimed in claim 1 wherein current through the primary windings is constrained by a common component.
9. A converter as claimed in claim 1 further comprising a clamp coupled to each switch to limit voltage across the switch when the switch is turned off.
10. A converter as claimed in claim 9 wherein the clamp is a diode.
11. A converter as claimed in claim 1 wherein a capacitor, primary winding and switch are connected in series in different orders in each of plural legs across the input, the current feed circuitry including a current constraining component connecting nodes within each of respective legs.
12. A converter as claimed in claim 11 wherein the current constraining component is an inductor.
13. A converter as claimed in claim 12 wherein each leg includes a primary winding between a capacitor and switch.
14. A converter as claimed in claim 13 wherein the inductor connects nodes between the primary winding and capacitor of each leg.
15. A converter as claimed in claim 13 wherein the inductor connects nodes between the primary winding and switch of each leg.
16. A converter as claimed in claim 1 wherein the switches are turned on with a fixed duty cycle.
17. A converter as claimed in claim 1 wherein the secondary circuit comprises synchronous rectifiers.
18. A power converter comprising:
an input which receives an input voltage and an input current from a DC source;
a first circuit leg comprising a capacitor, transformer primary winding and switch connected in series across the input;
a second circuit leg comprising a capacitor, transformer primary winding and switch connected in series across the input in an opposite order relative to the series connection of the first circuit leg;
an inductor interconnecting like nodes of the first and second circuit legs; and
a secondary circuit driven by the primary windings to provide a DC output.
19. A converter as claimed in claim 18 wherein the switches are turned on with a fixed duty cycle.
20. A converter as claimed in claim 18 wherein the secondary circuit comprises synchronous rectifiers.
21. A power converter as claimed in claim 18 wherein current flows through secondary winding as it flows through a respective primary winding.
22. A method of converting DC to DC voltage comprising:
providing an input voltage and an input current at an input;
dividing the input voltage across plural capacitors;
periodically switching transformer primary windings across the capacitors;
applying current of each of the primary windings through a magnetic element having DC current therethrough to constrain DC current flow through each primary winding as current flows through the winding; and
driving a secondary circuit from the primary windings to provide an output, current flowing through a secondary winding as current flows through a respective primary winding.
23. A method as claimed in claim 22 wherein two capacitors are connected across the input, each capacitor charging to about one-half the input voltage.
24. A method as claimed in claim 23 wherein each of the switches conducts about twice the input current.
25. A method as claimed in claim 22 wherein transformer secondary windings of the secondary circuit are not tightly coupled.
26. A method as claimed in claim 25 wherein first and second pairs of primary and secondary windings are provided on separate transformers.
27. A method as claimed in claim 22 wherein the magnetic element is an inductor.
28. A method as claimed in claim 22 wherein the magnetic element is a transformer.
29. A method as claimed in claim 22 wherein current through the primary windings is constrained by a common component.
30. A method as claimed in claim 22 further comprising limiting voltage across the switch when the switch is turned off.
31. A method as claimed in claim 30 wherein the voltage is limited with a diode.
32. A method as claimed in claim 22 wherein a capacitor, primary winding and switch are connected in series in different orders in each of plural legs across the input, the current being constrained by a component connecting nodes within each of respective legs.
33. A method as claimed in claim 32 wherein the current constraining component is an inductor.
34. A method as claimed in claim 33 wherein each leg includes a primary winding between a capacitor and switch.
35. A method as claimed in claim 34 wherein the inductor connects nodes between the primary winding and capacitor of each leg.
36. A method as claimed in claim 34 wherein the inductor connects nodes between the primary winding and switch of each leg.
37. A method as claimed in claim 22 wherein the switches are turned on with a fixed duty cycle.
38. A method as claimed in claim 22 wherein the secondary circuit comprises synchronous rectifiers.
39. A method as claimed in claim 22 wherein current flow is constrained by distinct current feed circuitry coupled to the primary windings.
40. A current fed DC to DC power converter comprising:
an input which receives an input voltage and an input current from a DC source;
capacitors connected across the input and dividing the input voltage therebetween;
transformer primary windings;
switch means for periodically switching the primary windings across respective capacitors;
current feed means having DC current flow therethrough that flows through each of the primary windings for constraining current flow through the primary windings; and
a secondary circuit driven by the primary windings to provide a DC output, current flowing through a secondary winding as current flows through a respective primary winding.