Over power protection for power converter
A power conversion circuit is provided. A power level of the power conversion circuit is determined by taking a first sample of a voltage potential of a resonant capacitor at a first time. A second sample of the voltage potential of the resonant capacitor voltage is taken at a second time. An electric current is determined based on the first sample and second sample.
1. A power conversion circuit, comprising:
an average current circuit including an input coupled for receiving a sampling signal representative of a current through a primary winding, wherein the average current circuit measures the sampling signal at a first time and a second time;
a power level circuit including a first input coupled to an output of the average current circuit and a second input coupled for receiving an input voltage of the power conversion circuit to determine an input power of the power conversion circuit as a product of the input voltage and a difference between the measurements of the sampling signal at the first time and second time;
a first amplifier including a first input coupled for receiving a power reference and a second input coupled to an output of the power level circuit;
a variable feedback clamp including a control input coupled to an output of the first amplifier; and
a second amplifier including a first input coupled for receiving the sampling signal and a second input coupled to the variable feedback clamp and further coupled for receiving a feedback signal of the power conversion circuit.
2. The power conversion circuit of claim 1 , further including:
a first power transistor including a first conduction terminal coupled for receiving the input voltage, a second conduction terminal coupled to the primary winding, and a control input coupled to an output of the second amplifier; and
a second power transistor including a first conduction terminal coupled to the second conduction terminal of the first transistor, a second conduction terminal coupled to a ground terminal, and a control input coupled to the output of the second amplifier.
3. The power conversion circuit of claim 2 , further including a driver logic circuit including an input coupled to the output of the second amplifier, a first output coupled to the control input of the first power transistor, and a second output coupled to the control input of the second power transistor.
4. The power conversion circuit of claim 1 , further including a voltage offset circuit coupled between the sampling signal and the first input of the second amplifier.
5. The power conversion circuit of claim 1 , further including:
a first circuit node adapted for coupling to the primary winding of the power conversion circuit;
a resonant capacitor coupled between the first circuit node and a ground terminal;
a first capacitor coupled between the first circuit node and a second circuit node; and
a second capacitor coupled between the second circuit node and ground terminal, wherein the second circuit node provides the sampling signal.
6. The power conversion circuit of claim 5 , further including a resistor coupled between the second circuit node and the ground terminal.
7. A power conversion circuit, comprising:
an average current circuit including an input coupled for receiving a sampling signal representative of a current through a primary winding, wherein the average current circuit measures the sampling signal at a first time and a second time; and
a power level circuit including a first input coupled to an output of the average current circuit and a second input coupled for receiving an input voltage of the power conversion circuit to determine an input power of the power conversion circuit as a product of the input voltage and a difference between the measurements of the sampling signal at the first time and second time.
8. The power conversion circuit of claim 7 , further including a first amplifier including a first input coupled for receiving a power reference and a second input coupled to an output of the power level circuit.
9. The power conversion circuit of claim 8 , further including:
a variable feedback clamp including a control input coupled to an output of the first amplifier; and
a second amplifier including a first input coupled for receiving the sampling signal and a second input coupled to the variable feedback clamp and further coupled for receiving a feedback signal of the power conversion circuit.
10. The power conversion circuit of claim 9 , further including:
a first power transistor including a first conduction terminal coupled for receiving the input voltage, a second conduction terminal coupled to the primary winding, and a control input coupled to an output of the second amplifier; and
a second power transistor including a first conduction terminal coupled to the second conduction terminal of the first transistor, a second conduction terminal coupled to a ground terminal, and a control input coupled to the output of the second amplifier.
11. The power conversion circuit of claim 10 , further including a driver logic circuit including an input coupled to the output of the second amplifier, a first output coupled to the control input of the first power transistor, and a second output coupled to the control input of the second power transistor.
12. The power conversion circuit of claim 9 , further including a voltage offset circuit coupled between the sampling signal and the first input of the second amplifier.
13. The power conversion circuit of claim 7 , further including:
a first circuit node adapted for coupling to the primary winding of the power conversion circuit;
a resonant capacitor coupled between the first circuit node and a ground terminal;
a first capacitor coupled between the first circuit node and a second circuit node; and
a second capacitor coupled between the second circuit node and ground terminal, wherein the second circuit node provides the sampling signal.
14. A method of determining an input power for a power conversion circuit, comprising:
measuring a sampling signal representative of a current through a primary winding at a first time and a second time; and
determining the input power as a product of an input voltage of the power conversion circuit and a difference between the measurements of the sampling signal at the first time and second time.
15. The method of claim 14 , further including comparing the determined input power and a power reference.
16. The method of claim 15 , further including clamping a feedback signal of the power conversion circuit in response to comparing the determined input power and the power reference.
17. The power conversion circuit of claim 16 , further including comparing the sampling signal to the clamped feedback signal.
18. The power conversion circuit of claim 17 , further including controlling a power transistor in response to comparing the sampling signal to the clamped feedback signal.
19. The method of claim 14 , further including sensing the current through the primary winding as a voltage across a resonant capacitor.
20. The method of claim 19 , further including dividing down the voltage across the resonant capacitor as the sampling signal.