Automatic over-current protection of transistors

Details Automatic over-current protection of transistors Automatic over-current protection of transistors

2000-02-23

2001-12-11

Sherry, Michael J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific current responsive fault sensor

C361S086000

Reexamination Certificate

active

06330143

ABSTRACT:

TECHNICAL FIELD
The present invention relates to power transistors and methods and circuits for protecting such transistors from damage due to fault currents.
BACKGROUND ART
Currently, there exists numerous converters which utilize power transistors. One application of power transistors is in conventional power supplies. In a power supply, the power transistors are used to switch high voltages. Such converters which utilize power transistors may be subjected to fault currents. A fault current through the power transistor causes serious damage to the power transistor as well as other components of the converter. These fault currents may be a product of short circuits or current shoot-through.
The prior art has responded to the above-referenced problems by offering complex protection circuits having multiple circuit devices. Such circuits include delay protection circuits for current shoot-through, and protection circuits for short circuits. The addition of the referenced protection circuits are not only in many instances slow to react to a detected fault current but are also costly to implement. One common scheme, desat protection, must be disabled during and shortly after switching times. Another common scheme, phase current protection, does not measure device current and thus cannot protect against shoot-through.
As such, a need exists for a new and improved protection circuit for a power transistor. The new and improved protection circuit must be capable of reacting quickly to a fault current, and must contain minimal additional components such that the protection circuit is low in cost without compromising reliability.
DISCLOSURE OF INVENTION
Accordingly, an object of the present invention is to provide a method and circuit for detecting fault currents through a power transistor circuit and providing a signal to shut down the power transistor.
In accordance with this and other objects, the present invention provides a circuit and method for detecting a fault current through a power transistor. A power transistor's inherent parasitic inductance is utilized to sense a change in current through the power transistor. When the voltage across the parasitic inductor exceeds a predefined limit a comparator circuit triggers a gate drive circuit. The comparator circuit causes the gate drive circuit to switch off the power transistor. Thus, the present invention is capable of reacting quickly to fault currents through the power transistor, thereby protecting the transistor and other circuit components from damage.
Thus, in accordance with one aspect of the present invention, a protection circuit is provided for protecting a power transistor from damage by sensing a change in current though the power transistor. The circuit includes a parasitic inductance inherent to the power transistor. A voltage is generated across the parasitic inductance when a change in current occurs through the power transistor. The voltage varies proportionally with the change in current through the power transistor. A comparator in communication with the parasitic inductance and a gate drive circuit is utilized to trigger the gate drive circuit to shut down the power transistor when the voltage exceeds a predefined value. The present invention contains a minimal number of components, reacts quickly to prevent damage, and is relatively inexpensive.
In accordance with another aspect of the invention, a method is provided for protecting a power transistor from being damaged by sensing a change in current through the power transistor. The method comprises detecting a change in current through the power transistor by measuring a voltage on the existing power transistor terminals using a voltage measurement circuit and activating a gate drive circuit to shut down the power transistor when the voltage exceeds a predefined value. The method according to the present invention prevents a power transistor from being damaged by reacting quickly to a change in current through the power transistor wherein a large change in current is indicative of a circuit fault.
The above object and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the best mode for carrying out the invention when taken in connection with the accompanying drawings.


REFERENCES:
patent: 3931567 (1976-01-01), Kostecki
patent: 4034280 (1977-07-01), Cronin et al.
patent: 4278930 (1981-07-01), Rogers
patent: 4338646 (1982-07-01), Davis et al.
patent: 4428015 (1984-01-01), Nesler
patent: 4525765 (1985-06-01), Brajder
patent: 4538198 (1985-08-01), Imanishi et al.
patent: 4651252 (1987-03-01), Babinski
patent: 4771357 (1988-09-01), Lorincz et al.
patent: 4862018 (1989-08-01), Taylor et al.
patent: 4893158 (1990-01-01), Mihara et al.
patent: 5325258 (1994-06-01), Choi et al.
patent: 5563759 (1996-10-01), Nadd
patent: 6097582 (2000-08-01), John et al.

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