Short circuit power limiter

Details Short circuit power limiter Short circuit power limiter

2001-01-09

2004-04-06

Toatley, Jr., Gregory J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Impedance insertion

C361S093100, C361S093900, C361S094000, C361S100000, C361S101000

Reexamination Certificate

active

06717783

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates generally to integrated circuits (ICs) and more particularly to a short circuit power limiter that limits and controls power consumption during short circuit conditions.
Short circuit current limiting has long been used to protect the output transistors during short circuit events. With amplifiers for example, if the current is not limited, excess power consumed by the output transistors could be too great resulting in permanent physical damage to the amplifier.
FIG. 1
a
shows a simplified high-level block diagram of a conventional amplifier, according to the prior art. Under existing current limiting schemes, the average power consumed by an amplifier is at its maximum value during a short circuit event. To withstand this maximum value, the amplifier must be sufficiently robust. Conventional ways to make it robust include oversized on-chip metal routing and die size, special IC packaging, and external heat sinks. Each of these solutions, however, increases the overall system cost.
SUMMARY OF THE INVENTION
The present invention provides a short circuit power limiter which limits power consumption during a current-limited short circuit event. When a short circuit sensor detects a short circuit condition in a target circuit, the sensor sends a short circuit flag signal to the power limiter. The power limiter then reduces the power consumption of the circuit. In a specific example, the power limiter toggles particular portions of the circuit on and off to reduce the circuit's average short circuit power consumption.
The description of the present invention uses the term short circuit “power limiting” and is distinguished from, and in addition to, existing short circuit “current limiting” schemes. The present invention provides a circuit and a method for reducing the short circuit power consumption of a circuit to, in one embodiment, a value below that of normal operation power consumption. Because the present invention reduces the worst case power consumption, it also reduces the cost of implementing circuits that might have short circuit problems, such as amplifier circuits. As a result, the present invention provides an optimal physical design that is economically feasible. In another embodiment, by periodically turning on the circuit, instead of simply turning it off, the current can be sensed to determine if the short-circuit condition is continuing or not.
In one embodiment, the short circuit power limiter circuit has an input terminal coupled to receive a short circuit flag signal from the current sensor. The current sensor is configured to couple to a target circuit, such as an output buffer of an amplifier. The power limiter is configured to send a tri-state signal to the output buffer in response to the short circuit flag signal during short circuit conditions, and also configured to assert the tri-state signal for a duration of &tgr;
2
seconds. The limiter circuit disables the output buffer for a duration of &tgr;
2
seconds and enables the output buffer for a duration of &tgr;
1
seconds, repeating such a cycle as long as a short circuit condition exists.
In another embodiment, the short circuit flag signal goes low during a short circuit event. In another embodiment, the power limiter circuit also includes a counter configured to generate the tri-state signal.
The present invention achieves the above purposes and benefits in a simple, versatile, and reliable circuit and method that is readily suited to the widest possible utilization. The present invention achieves these purposes and benefits in the context of known circuit technology and known techniques in the electronic arts. Further understanding, however, of the nature, objects, features, and advantages of the present invention is realized by reference to the latter portions of the specification, accompanying drawings, and appended claims. Other objects, features, and advantages of the present invention will become apparent upon consideration of the following detailed description, accompanying drawings, and appended claims.


REFERENCES:
patent: 6469575 (2002-10-01), Oki et al.

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