Apparatus and method for deactivating an on-switch of a circuit for a variable time interval
AssigneeNational Semiconductor Corporation
InventorsRobert Henry Bell, Steven Michael Barrow
Life of this patent
Estimating the term…
Abstract
A pulse frequency modulation switching regulator varies the forced off-time of a load circuit when the load circuit is subject to an overload or short circuit event. An on-switch of the circuit is deactivated for a variable time interval when an output current of the load circuit exceeds a threshold. The time interval that the on-switch is deactivated is dependent on an output voltage of the load circuit. The on-switch is deactivated for a short time interval when the load circuit is subject to a slight overload. The on-switch is deactivated for a long time interval when the load circuit is subject to a short circuit.
Claims16
An apparatus for providing a limit signal when a current provided by an on-switch to a load circuit exceeds a threshold, comprising:
- a current limit time control circuit that is arranged to assert the limit signal for a variable time interval when activated;
- a current sense circuit that is arranged to activate the current limit time control circuit when the current exceeds the threshold;
- and
- a time adjustment circuit that is arranged to adjust the variable time interval in response to an output voltage associated with the load circuit.
A method for providing a limit signal when a current provided by an on-switch to a load circuit exceeds a threshold, comprising:
- sensing the current;
- activating a time control circuit when the sensed current exceeds the threshold;
- asserting the limit signal for a variable time interval when the time control circuit is activated;
- and
- adjusting the variable time interval in response to an output voltage associated with the load circuit.
An apparatus for providing a limit signal when a current provided by an on-switch to a load circuit exceeds a threshold, comprising:
- a means for sensing the current;
- a means for activating a time control circuit when the sensed current exceeds the threshold;
- a means for asserting the limit signal for a variable time interval when the time control circuit is activated;
- and
- a means for adjusting the variable time interval in response to an output voltage associated with the load circuit.
Dependencies are inferred from the claim text.