Overcurrent protection device and method of operating a power switch
View Patent ↗An overcurrent protection device comprises a maximum-allowed-current unit and a power switch. The maximum-allowed-current unit determines a maximum allowed current in real-time. The maximum allowed current is determined at least partially on an instantaneous level of a load voltage. The load voltage is a voltage across a load to be powered. The power switch is connectable with a switch input to a voltage supply and with a switch output to the load, for providing power to said load. The power switch has a conductive state and a nonconductive state, and is arranged to assume the nonconductive state in response to an indication that a current through the power switch is exceeding the maximum allowed current. A method of operating a power switch is also described.
1. An overcurrent protection device, comprising:
a maximum-allowed-current unit configured to determine a maximum allowed current in real-time, wherein said maximum allowed current is determined based on a selected one of a plurality of maximum allowed current profiles stored in a memory, and wherein the selected maximum allowed current profile is based on an instantaneous level of a supply voltage, and said supply voltage is a voltage across the overcurrent protection device and a load to be powered; and
a power switch connectable with a switch input to a voltage supply and with a switch output to said load, and configured to provide power to said load, wherein said power switch has a conductive state and a nonconductive state, and the power switch is arranged to assume the nonconductive state in response to an indication that a current through the power switch is exceeding the maximum allowed current; and
a turn-on detector to communicate with the power switch, the turn-on detector to detect a turn-on event for the power switch in response to a first edge of a pulse width modulation control signal, to trigger a first edge of a turn-on detection signal in response to the first edge of the pulse width modulation control signal, and to trigger a second edge in the turn-on detection signal in response to a second edge of the pulse width modulation control signal with a particular amount of delay from the first edge of the pulse width modulation control signal being detected.
2. The overcurrent protection device as set forth in claim 1 , wherein the power switch is arranged to pass from the nonconductive state into the conductive state via at least one intermediate state.
3. The overcurrent protection device as set forth in claim 1 , wherein the maximum-allowed-current unit is operable to determine the maximum allowed current in real-time during a transition of the power switch from the nonconductive state to the conductive state.
4. The overcurrent protection device as set forth in claim 1 , wherein the maximum-allowed-current unit is operable to further determine the maximum allowed current as a product of a first function and a second function, the first function being a function of one or more of a time and a temperature, and the second function being a function of a load voltage.
5. The overcurrent protection device as set forth in claim 4 , wherein said first function allows an inrush current to flow through the power switch during a first period, and the inrush current is higher than a maximum allowed current during a subsequent second period.
6. The overcurrent protection device as set forth in claim 4 , wherein said first function is a function of an accumulated time during which the power switch is in the conductive state.
7. The overcurrent protection device as set forth in claim 1 , wherein the maximum-allowed-current unit comprises a memory containing data for determining the selected maximum allowed current profile as a function of at least a voltage variable.
8. The overcurrent protection device as set forth in claim 1 , wherein the maximum-allowed-current unit is operable to determine the maximum allowed current as an increasing function of the supply voltage.
9. The overcurrent protection device as set forth in claim 1 , wherein the maximum-allowed-current unit is operable to determine the maximum allowed current such that the maximum allowed current is positive when the supply voltage is zero.
10. The overcurrent protection device as set forth in claim 1 , wherein the maximum-allowed-current unit is operable to further determine the maximum allowed current as a bounded function of a load voltage.
11. The overcurrent protection device as set forth in claim 1 , comprising a switch controller for setting the power switch alternatively into the conductive state and into the nonconductive state in response a pulse width modulated control signal.
12. The overcurrent protection device as set forth in claim 1 wherein
the turn-on event comprises the pulse width modulated control signal indicating, during an interval having a length of at least a minimum off-time, that the power switch is to assume the nonconductive state, followed by the pulse width modulated control signal indicating that the power switch is to assume the conductive state.
13. The overcurrent protection device as set forth in claim 1 , wherein the load is a lamp.
14. A method of operating a power switch, wherein the power switch has a conductive state and a nonconductive state and the method comprises:
connecting a load in series with the power switch;
applying a supply voltage across the load and the switch, for powering the load, to generate a load voltage, said load voltage being a voltage across the load;
determining in real-time a maximum allowed current at least partially on an instantaneous level of the supply voltage based on a selected one of a plurality of maximum allowed current profiles stored in a memory, and wherein the selected maximum allowed current profile is based on the supply voltage;
setting the power switch into the nonconductive state in response to an indication that a current through the power switch is exceeding the maximum allowed current;
detecting a turn event for the power switch in response to a first edge of a pulse width modulation control signal;
triggering a first edge of a turn-on detection signal in response to the first edge of the pulse width modulation control signal; and
triggering a second edge in the turn-on detection signal in response to a second edge of the pulse width modulation control signal with a particular amount of delay from a first edge of the width modulation control signal detected.
15. The method as set forth in claim 14 , wherein said determining comprises:
determining said maximum allowed current in real-time during a transition of the power switch from the nonconductive state to the conductive state.
16. The method as set forth in claim 14 , wherein said determining comprises:
determining said maximum allowed current further as a product of a first function and a second function, wherein the first function is a function of one or more of a time and temperature, and the second function is a function of the load voltage.
17. The method of as set forth in claim 16 wherein said first function is a function of an accumulated time during which the power switch is in the conductive state.
18. The method as set forth in claim 14 , wherein said determining comprises:
determining said maximum allowed current further as an increasing function of the load voltage.
19. The method as set forth in claim 14 , wherein said determining comprises:
determining said maximum allowed current as a bounded function of the load voltage.