Short circuit protection
AssigneeNational Semiconductor Corporation
InventorsDanny D'Aquino, Mehmet Aslan
Life of this patent
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Abstract
Output current of an amplifier is limited by clamping the voltage at the gate of one or more of the transistors in the output stage. A drive signal is provided to the gate of a p-type transistor in an example output stage. Another p-type transistor is activated in a short-circuit protection circuit when the drive signal is below a pre-determined level, whereby the short-circuit protection circuit is activated to clamp the drive signal. Similarly, an n-type transistor in another short-circuit protection circuit may be configured to clamp another drive signal for an n-type output stage. The short-circuit protection methodology may be applied to output stages such as in class A and class AB amplifiers.
Claims20
A circuit for short circuit protection comprising:
- a first transistor having a gate that is configured to receive an input signal of the short circuit protection circuit, wherein the first transistor is configured to activate when a voltage associated with the input signal reaches a first pre-determined voltage level;
- a clamping circuit that is coupled to a source of the first transistor, the clamping circuit being configured to adjust the first pre-determined voltage level;
- and
- a current mirror circuit that is coupled to a drain of the first transistor, the current mirror circuit being configured to adjust an output signal of the short circuit protection circuit when the voltage associated with the input signal exceeds the first pre-determined voltage level.
An amplifier circuit with short circuit protection comprising:
- a differential amplifier circuit having first and second inputs that are configured to receive a differential input signal;
- an output stage comprising an output transistor, the output transistor having a gate that is configured to receive a first signal, and a drain that is coupled to the differential amplifier circuit such that the amplifier circuit is arranged in closed loop operation;
- and
- a first short circuit protection circuit that is responsive to the first signal, comprising:
- a first transistor having a gate that is coupled to the gate of the output transistor;
- a first clamping circuit that is coupled to the source of the first transistor;
- and
- a first current mirror circuit having a first port that is coupled to a drain of the first transistor and a second port that is coupled to a first output of the differential amplifier.
A method for an amplifier circuit in closed loop operation having an output stage with an output transistor, the method comprising:
- evaluating a drive voltage that is associated with the gate of the output transistor;
- determining when the drive voltage is within a pre-determined voltage range, wherein the pre-determined voltage range is associated with a high load condition on the output stage;
- providing current in response to the drive voltage when the drive voltage is within the pre-determined voltage range;
- and
- coupling the current to a node that is coupled to the gate of the output transistor such that the drive voltage is clamped when the drive voltage is within the pre-determined voltage range.
A circuit protection circuit for an amplifier circuit in closed loop operation having an output stage comprising an output transistor, the short circuit protection circuit comprising:
- a means for evaluating that is configured to evaluate a drive voltage that is associated with the gate of the output transistor;
- a means for determining that is configured to determine when the drive voltage is within a pre-determined voltage range, wherein the pre-determined voltage range is associated with a high load condition on the output stage;
- a means for providing current that is configured to provide current in response to the drive voltage when the drive voltage is within the pre-determined voltage range;
- and
- a means for clamping that is configured to couple the current to a node that is coupled to the gate of the output transistor such that the drive voltage is clamped when the drive voltage is within the pre-determined voltage range.
Dependencies are inferred from the claim text.