Zero-current switching forward power conversion

Claim 2

A zero-current switching forward converter circuit comprising: a power transformer including a primary and a secondary winding, said power transformer being constructed to have an effective secondary leakage inductance L2e; a first switching device connected for selectively coupling a power source across the primary winding of said power transformer; a first unidirectional conducting device connected in series with said secondary winding and oriented to conduct during conduction by said first switching device; and a capacitor of capacitance C connected in series with said secondary winding and said first unidirectional conducting device; said circuit being characterised in that a controller is provided, having means adapted for selectively closing and opening said first switching device to operatively transfer power from said voltage source via the effective leakage inductance of said transformer to charge said capacitance during an energy transfer cycle having a characteristic time scale of π √ L2e*C; in that a second switching device is connected on the secondary side of said transformer; and in that said controller includes a second control means adapted for opening and closing said second switching device to selectively govern the amount of energy transferred during said energy transfer cycle.

Claim 3

A circuit according to Claim 1, further characterised in that said second switching device is connected to prevent charging of said capacitor when said second switching device is closed.

Claim 4

A circuit according to Claims 1 or 2, further characterised in that said second switching device is connected to parallel with said capacitor.

Claim 5

A circuit according to Claim 3, further characterised in being adapted to supply power to a load, said circuit further comprising an inductor arranged to be operatively connected in series between said capacitor and the load to deliver current to the load.

Claim 6

A circuit according to Claim 4, further characterised in that said second control means comprises means adapted for detecting closure of said first switching device; and means adapted for opening said second switching device at substantially the same time that said first switching device is closed.

Claim 7

A circuit according to any of Claims 3, 4 or 5, further characterised in that said second switching device comprises a switch capable of unidirectional conduction when closed, and a second unidirectional conduction device, said switch and said unidirectional conduction device being connected in parallel and oriented to conduct in opposite directions.

Claim 8

A circuit according to Claim 6, further characterised in that said second switching device is oriented so that said unidirectional conduction device will prevent charging of said capacitor when current flowing in said second inductor is in a direction towards the load.

Claim 9

A circuit according to Claim 1, further characterised in that said second switching device is connected in parallel with the secondary winding of said power transformer.

Claim 10

A circuit according to Claim 8, further characterised in that a second unidirectional conducting device is connected in parallel with said capacitor and oriented to prevent charging of said capacitor when current flowing in said second inductor is in a direction towards a load.

Claim 11

A circuit according to Claim 9, further characterised in being adapted to accept a load, said circuit further comprising an inductor arranged for connection in series between said capacitance and the load to deliver current to the load.

Claim 12

A circuit according to any of Claims 4, 7, or 10, further characterised in that said second control means comprises means for detecting closure of said first switching device, and means for opening said second switching device at a selected time thereafter.

Claim 13

A circuit according to Claims 5 or 11, further charcterised in that said second control means further comprises means adapted for detecting voltage across said capacitor, and means adapted for closing said second switching device when voltage across said capacitor is substantially zero.

Claim 14

A circuit according to Claim 3, further characterised in being adapted for delivering power to two or more independent loads, said circuit further comprising a primary inductor arranged for connection in series with said capacitor and one of said independent loads; and a plurality of secondary windings magnetically coupled to said primary inductor, said secondary windings respectively having relative numbers of turns that corresponds to the relative voltages to be delivered respectively to said independent loads.

Claim 15

A circuit according to Claim 13, further characterised in that each said secondary winding is connected via a subcircuit adapted for connection to a respective said independent load, which subcircuit includes a secondary unidirectional conducting device oriented to conduct current when the voltage across said primary inductor is positive in a direction between said load and said capacitor.

Claim 16

A circuit according to Claim 14, further characterised in that each said subcircuit includes a filter element adapted for smoothing the voltage across said independent load.

Claim 17

A circuit according to Claim 15, further characterised in that said filter element comprises a capacitor arranged for connection in parallel with said load.

Claim 18

A circuit according to any of Claims 14, 15 or 16, further characterised in that each said subcircuit comprises a post-regulator adapted for regulating the voltage delivered to said independent load.

Claim 19

A circuit according to Claim 17, further characterised in that each said secondary winding is loosely magnetically coupled to said primary inductor.

Claim 20

A circuit according to Claim 17 or 18, further characterised in that said post-regulator comprises a reset magnetic amplifier.

Claim 21

A circuit according to Claims 17 or 18, further characterised in that said post-regulator comprises a dissipative regulator.

Claim 22

A zero-current switching forward converter circuit comprising: a voltage source; a load; a power transformer including a primary and a secondary winding, said power transformer being constructed to have an effective secondary leakage inductance L2e; a first switching device connected to selectively couple said power source across the primary winding of said power transformer; a first unidirectional conducting device connected in series with said secondary winding and oriented to conduct during conduction by said first switching device; and a capacitor of capacitance C connected in series with said secondary winding and said first unidirectional conducting device; said circuit being characterised in that a controller is provided, having means adapted for selectively closing and opening said first switching device to operatively transfer power from said voltage source via the effective leakage inductance of said transformer to charge said capacitance during an energy transfer cycle having a characteristic time scale of π √ L2e*C; in that a second switching device is connected on the secondary side of said transformer and in parallel with said capacitor to prevent charging of said capacitor when said second switching device is closed; in that an inductor is connected in series between said capacitor and the load to deliver current to the load; and in that said controller includes a second control means adapted for opening and closing said second switching device to selectively govern the amount of energy transferred during said energy transfer cycle.

Claim 23

A zero-current switching forward converter circuit comprising: a voltage source; a load; a power transformer including a primary and a secondary winding, said power transformer being constructed to have an effective secondary leakage inductance L2e; a first switching device connected to selectively couple said power source across the primary winding of said power transformer; a first unidirectional conducting device connected in series with said secondary winding and oriented to conduct during conduction by said first switching device; and a capacitor of capacitance C connected in series with said secondary winding and said first unidirectional conducting device; said circuit being characterised in that a controller is provided, having means adapted for selectively closing and opening said first switching device to operatively transfer power from said voltage source via the effective leakage inductance of said transformer to charge said capacitance during an energy transfer cycle having a characteristic time scale of π √ L2e*C; in that a second switching device is connected on the secondary side of said transformer and in parallel with said capacitor to prevent charging of said capacitor when said second switching device is closed; in that an inductor is connected in series between said capacitor and the load to deliver current to the load; and in that said controller includes a second control means adapted for opening and closing said second switching device to selectively govern the amount of energy transferred during said energy transfer cycle.

Claim 27

A method according to Claim 23, wherein an inductor is connected in series between said capacitor and a load, the method being further characterised in that in a reverse boost mode said second switching device is closed when the voltage across said capacitor is substantially zero to prevent reverse current in said inductor from transferring energy to said capacitor.

Claim 29

A method according to Claim 25, further characterised in that the frequency at which said first switch is opened and closed is varied to effect output voltage regulation.

Claim 31

A method according to Claim 23, further characterised in that in a forward boost mode said second switching device is held closed for a selected period of time after said first switching device has been closed.

Claim 33

A method according to Claim 29, further characterised in that the frequency at which said first switch is opened and closed is varied to effect output voltage regulation when the ratio of the value of said voltage source to the value of the output voltage of the converter is greater than the ratio of the number of turns on the primary of said power transformer to the number of turns on the secondary of said power transformer.

Claim 34

A method according to Claim 30, further characterised in that the time period during which the second switching device remains closed is controlled so as to maintain the output voltage of the converter circuit in regulation irrespective of the relative values of said voltage source and said output voltage.

Claim 35

A method according to Claim 31, wherein said voltage source has a possibly varying voltage level, said method being further characterised in that said second switching device is opened when the level of said current flowing in said first unidirectional conduction device rises to become equal to the level of current flowing in the direction of the load in said second inductor so long as said voltage level does not fall below a predetermined value, and is otherwise controlled to stay closed for a longer time period to maintain said output voltage of the converter circuit in regulation.

Claim 36

A method according to Claim 29, wherein the ratio of the number of turns on the primary of said power transformer to the number of turns on the secondary of said power transformer is greater than the ratio of the maximum value of the voltage source to the value of the output voltage of the circuit, the method being further characterised in that the opening and closing of said first switching device is controlled to occur at a constant frequency.

Claim 37

A method according to Claim 33, further characterised in that the time period during which the second switching device remains closed is controlled so as to maintain the output voltage of the converter circuit in regulation.