Circuit and method for limiting power to a load
View Patent ↗A circuit and method for limiting the power supplied to a load are provided. The circuit and method prevent power supplied to the load from exceeding a power threshold for a programmable amount of time specified in a timer. The circuit includes a voltage controlled current source coupled to the load. A current multiplier divider is coupled to the voltage controlled current source and a timer is coupled to the load. A comparator with an adaptive threshold is coupled to the current multiplier divider and the input for controlling the timer to limit the power supplied to the load.
1. A circuit for use with an input voltage to limit the power supplied to a load, comprising an input adapted to receive the input voltage, a current mirror, a voltage controlled current source coupled to the load for providing an input current and coupled to the current mirror for generating a first input current equal to the input current, a current multiplier divider coupled to the voltage controlled current source, a comparator coupled to the current multiplier divider and the input to provide an output, and a timer coupled to the comparator to discontinue the power supplied to the load based at least on the output of the comparator.
2. The circuit of claim 1 , wherein the current mirror is coupled between the voltage controlled current source and the current multiplier divider.
3. The circuit of claim 1 , further comprising a biasing circuit coupled to the current multiplier divider for providing the first input current and a second input current to the current multiplier divider.
4. The circuit of claim 3 , wherein the current multiplier divider provides an output current based upon the first input current, the second input current and the input current provided by the voltage controlled current source.
5. A circuit for use with an input voltage to limit the power supplied to a load, comprising an input adapted to receive the input voltage, a voltage controlled current source coupled to the load for providing an input current, a current multiplier divider coupled to the voltage controlled current source, a comparator coupled to the current multiplier divider and the input to provide an output, a current controlled voltage source coupled to the comparator to provide a current controlled adaptive voltage threshold as an input to the comparator, and a timer coupled to the comparator to discontinue the power supplied to the load based at least on the output of the comparator.
6. The circuit of claim 5 , wherein the comparator includes a differential comparator.
7. The circuit of claim 6 , further comprising a sensor resistor, a bypass capacitor, and a transistor coupled between the input and the load.
8. The circuit of claim 7 , further comprising a gate current source coupled to the transistor.
9. The circuit of claim 7 , wherein the timer is programmable and is coupled to a switch that turns off power to the load when the voltage across the sensor resistor exceeds the current controlled adaptive voltage threshold for an amount of time for which the timer is programmed.
10. A circuit for use with an input voltage to limit the power supplied to a load, comprising an input adapted to receive the input voltage, a current controlled voltage source coupled to a current multiplier divider for generating an adaptive voltage threshold, a sensor resistor coupled to the input between the input and the load, means for comparing a voltage across the sensor resistor to the adaptive voltage threshold and means for discontinuing power supplied to the load when the voltage across the sensor resistor exceeds the adaptive voltage threshold.
11. The circuit of claim 10 , wherein the means for comparing the voltage across the sensor resistor to the adaptive voltage threshold includes a comparator.
12. The circuit of claim 11 , wherein the means for discontinuing power supplied to the load includes a timer coupled to the comparator.
13. The circuit of claim 12 , wherein the timer is programmable and wherein the means for discontinuing power supplied to the load further includes a switch coupled to the timer and configured to turn off power to the load when the voltage across the sensor resistor exceeds the adaptive voltage threshold for an amount of time for which the timer is programmed.
14. A method for limiting power supplied to a load, comprising providing an input voltage at an input, generating a sensor voltage across a sensor resistor from the input voltage, generating a first current by coupling a voltage controlled current source to the load, generating a second current by coupling a current multiplier divider to the voltage controlled current source to provide a first input current based on the first current and to a biasing circuit to provide second and third input currents based on a reference current, controlling a voltage source with the second current to generate an adaptive voltage threshold, comparing the sensor voltage to the adaptive voltage threshold, and discontinuing power to the load when the sensor voltage exceeds the adaptive voltage threshold.
15. The method of claim 14 , wherein the comparing step includes comparing the sensor voltage to the adaptive voltage threshold using a comparator.
16. The method of claim 15 , further comprising turning off power to the load when the sensor voltage exceeds the adaptive voltage threshold for a programmable period of time.
17. A circuit for use with an input voltage to limit the power supplied to a load, comprising an input adapted to receive the input voltage, a biasing circuit for generating a reference current, a voltage controlled current source coupled to the load for providing an input current by generating a first current proportional to an output voltage to the load, a current multiplier divider coupled to the voltage controlled current source to receive a first input current equal to the first current and coupled to the biasing circuit to receive second and third input currents based on the reference current, the current multiplier divider generating a second current based on the first, second and third input currents, a comparator coupled to the current multiplier divider and the input to provide an output, and a timer coupled to the comparator to discontinue the power supplied to the load based at least on the output of the comparator.
18. The circuit of claim 10 , wherein the current multiplier divider is configured to receive a first input current proportional to an output voltage to the load and to receive second and third input currents based on a reference current, the current multiplier divider generating an output, and wherein the current controlled voltage source is coupled to the current multiplier divider to generate the adaptive voltage threshold based on the output.
19. The circuit of claim 5 , further comprising a current mirror coupled between the voltage controlled current source and the current multiplier divider.
20. The circuit of claim 5 , further comprising a biasing circuit coupled to the current multiplier divider for providing a first input current and a second input current to the current multiplier divider.
21. The circuit of claim 20 , wherein the current multiplier divider provides an output current based upon the first input current, the second input current and the input current provided by the voltage controlled current source.
22. The circuit of claim 17 , further comprising a current controlled voltage source coupled to the current multiplier divider to receive the second current and coupled to the comparator to provide a first output to the comparator based on the second current.
23. The circuit of claim 22 , further comprising a sensor resistor coupled between the input and the load and configured to provide a second output to the comparator, the comparator providing the output to the timer based on the first and second outputs.
24. The circuit of claim 1 , further comprising a current controlled voltage source coupled to the current multiplier divider to receive an output current of the current multiplier divider and coupled to the comparator to provide a first output to the comparator based on the output current.
25. The circuit of claim 24 , further comprising a sensor resistor coupled between the input and the load and configured to provide a second output to the comparator, the comparator providing the output to the timer based on the first and second outputs.