Power supply having a flyback topology and current sense transformer

1. Apparatus comprising:

a power supply having a flyback topology that comprises a flyback transformer and a current sense circuit that outputs a current signal indicative of a current output by the power supply;

wherein the current sense circuit comprises a current sense transformer coupled to the flyback transformer;

wherein the current signal is used to control the power output by the power supply; and

wherein the current signal is used to reduce a voltage output by the power supply when the current signal indicates that the current output by the power supply is greater than a maximum current for the power supply.

2. A power supply comprising:

a flyback transformer having a primary winding and a secondary winding;

a switch coupled to the primary winding of the flyback transformer, wherein the switch enables input current to flow through the primary winding of the flyback transformer when the switch is turned on and wherein the switch prevents the current from flowing through the primary winding of the flyback transformer when the switch is turned off;

a current sense transformer coupled to the secondary winding of the flyback winding, wherein the current sense transformer is used to generate a current signal indicative of a current output by the power supply; and

an operational amplifier having a first input coupled to the current signal and a second input coupled to a current reference signal indicative of a maximum current for the power supply;

wherein the current signal is used to control the switch.

3. The power supply of claim 2 , further comprising a controller that uses the current signal to control the switch.

4. The power supply of claim 3 , wherein the controller comprises a pulse width modulation controller that turns the switch on and off based on the current signal.

5. The power supply of claim 2 , further comprising a voltage sense circuit that outputs a voltage signal indicative of a voltage output by the power supply.

6. The power supply of claim 5 , wherein the voltage signal is used to control the switch.

7. The power supply of claim 6 , further comprising an operational amplifier having a first input coupled to the voltage signal and a second input coupled to a voltage reference signal indicative of a nominal voltage for the power supply.

8. The power supply of claim 2 , further comprising a flyback rectifier diode coupled to the secondary winding of the flyback transformer, wherein the rectifier diode rectifies the current flowing in the secondary winding of the flyback transformer.

9. The power supply of claim 2 , further comprising an output capacitor coupled across the secondary winding of the flyback transformer.

10. The power supply of claim 2 , further comprising an current sense circuit that outputs the current signal, wherein the current sense circuit includes the current sense transformer and an RC circuit that averages a current flowing in a secondary winding of the current sense transformer.