Logarithmic power compensation for a switching power supply

Claim 2

A circuit for controlling an output voltage, the circuit comprising: a transformer having a primary winding and a secondary winding; a first switch coupled in series with the primary winding, the first switch including a control terminal; a second switch coupled in series with the secondary winding, the second switch including a control terminal; a capacitor coupled in parallel with the second switch; a comparator having a first input coupled to a reference voltage node and a second input coupled to a node between the second winding and the second switch; and a drive circuit receiving an input signal from the comparator and being coupled to the control terminal of the first switch and to the control terminal of the second switch.

Claim 3

A circuit for controlling an output voltage, the circuit comprising: a transformer having a primary winding and a secondary winding; a first switch coupled in series with the primary winding, the first switch including a control terminal; a second switch coupled in series with the secondary winding, the second switch including a control terminal; a capacitor coupled in parallel with the second switch; a drive circuit for generating a first control signal and a second control signal, the first control signal being applied to the control terminal of the first switch and the second control signal being applied to the control terminal of the second switch, wherein the first control signal is a complement of the second control signal.

Claim 4

A circuit for controlling an output voltage, the circuit comprising: a transformer having a primary winding and a secondary winding; a first switch coupled in series with the primary winding, the first switch including a control terminal; a second switch coupled in series with the secondary winding, the second switch including a control terminal; a capacitor coupled in parallel with the second switch; a drive circuit for generating a first control signal and a second control signal, the first control signal being applied to the control terminal of the first switch and the second control signal being applied to the control terminal of the second switch, wherein the first control signal is a complement of the second control signal.

Claim 5

The circuit of claim 1 wherein the first and second switches comprise transistors.

Claim 6

The circuit of claim 3 wherein the first and second switches comprise field effect transistors.

Claim 7

The circuit of claim 1 and further comprising a resistive element coupled between the second winding and the second switch.

Claim 8

The circuit of claim 2 wherein the drive circuit receives a control input signal from a comparator, the comparator having a first input coupled to a reference voltage node and a second input coupled to a node between the second winding and the second switch.

Claim 9

The circuit of claim 1 wherein the circuit comprises a flyback converter.

Claim 10

The circuit of claim 1 wherein the drive circuit generates a first control signal and a second control signal, the first control signal being applied to the control terminal of the first switch and the second control signal being applied to the control terminal of the second switch.

Claim 13

The method of claim 9 wherein the input voltage comprises an unregulated DC voltage.

Claim 14

The method of claim 9 wherein the steps of allowing current to flow through the primary winding and preventing current from flowing through the primary winding are accomplished by controlling a second switch coupled in series with the primary winding.

Claim 15

The method of claim 11 and further comprising the steps of comparing a voltage across the capacitor with a control voltage and controlling the second switch based upon the result of the comparison.

Claim 16

The method of claim 12 wherein the step of rendering substantially conductive a switch is performed in response to the result of the comparison step.

Claim 17

An electrical circuit comprising: a transformer having a primary and a secondary winding, each of the windings having first and second terminals, the first terminal of the primary winding coupled to an input voltage node; a reference potential node; a first resistor with a current path coupled between the second terminal of the primary winding and the reference potential node; a first switch with a current path coupled between the second terminal of the primary winding and the reference potential node, the current path of the first switch coupled in series with the current path of the first resistor, the first switch further having a control input terminal; a diode with a first terminal coupled to the second terminal of the secondary winding; a second resistor with a first terminal coupled to a second terminal of the diode; a capacitor with a first terminal coupled to the reference potential node and a second terminal coupled to a second terminal of the second resistor; a second switch with a current path coupled between the second terminal of the second resistor and the reference potential node, the second switch also including a control terminal; a comparator for comparing a voltage at the second terminal of the capacitor with a control voltage; and a drive circuit for receiving an output of the comparator and for controlling the first and second switches.

Claim 18

An electrical circuit comprising: a transformer having a primary and a secondary winding, each of the windings having first and second terminals, the first terminal of the primary winding coupled to an input voltage node; a reference potential node; a first resistor with a current path coupled between the second terminal of the primary winding and the reference potential node; a first switch with a current path coupled between the second terminal of the primary winding and the reference potential node, the current path of the first switch coupled in series with the current path of the first resistor, the first switch further having a control input terminal; a diode with a first terminal coupled to the second terminal of the secondary winding; a second resistor with a first terminal coupled to a second terminal of the diode; a capacitor with a first terminal coupled to the reference potential node and a second terminal coupled to a second terminal of the second resistor; a second switch with a current path coupled between the second terminal of the second resistor and the reference potential node, the second switch also including a control terminal; a comparator for comparing a voltage at the second terminal of the capacitor with a control voltage; and a drive circuit for receiving an output of the comparator and for controlling the first and second switches.

Claim 19

The circuit of claim 14 wherein the drive circuit includes a first output coupled to the control terminal of the first switch and a second output coupled to the control terminal of the second switch.

Claim 20

The circuit of claim 14 wherein the first and second switches comprise transistors.

Claim 21

The circuit of claim 16 wherein the first and second switches comprise field effect transistors.

Claim 22

The circuit of claim 14 wherein the comparator includes a first input node to receive the reference voltage and wherein the circuit further comprises a clamping circuit coupled to the first input node.

Claim 23

The circuit of claim 18 wherein the clamping circuit comprises: a diode coupled to the first input node of the comparator; an amplifier with first and second inputs and an output, the first input and the output being coupled to the diode; and a summing circuit coupled to the second input of the amplifier.

Claim 24

The circuit of claim 14 and further comprising an error amplifier, the error amplifier receiving an output voltage and a reference voltage and generating the control voltage.