Electricity: power supply or regulation systems – Output level responsive – Using a three or more terminal semiconductive device as the...
Reexamination Certificate
1999-10-20
2001-04-17
Wong, Peter S. (Department: 2838)
Electricity: power supply or regulation systems
Output level responsive
Using a three or more terminal semiconductive device as the...
C361S018000
Reexamination Certificate
active
06218816
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electronic circuit that protects a system power supply from potential damage from a short-circuit or excess current situation. In particular, the present invention prevents the system power supply from “powering up” the system if it is in a short-circuit situation. The present invention also detects short-circuit and excess current situations after the system has been “powered up”, and, in such circumstances, cuts the system power supply off from the rest of the system to prevent possible damage to the power supply from excessive output current.
BACKGROUND
Power supplies in electronic systems, such as automobile electrical systems, are subject to potential damage if a short-circuit or an excess current condition occurs. Present technology protects system power supplies by using active current sensors to determine if excess current is drawn from the power supply. Other existing technology involves the use of heat sensing devices to determine if the load device in the system or the pass transistor in the power supply is conducting excessive heat. If excess current or excess heat is detected in the system, the electrical system is shut down prior to the power supply incurring any damage. However, the use of active current sensors and heat sensing devices is not as cost effective as using individual electronic components. Moreover, the use of active current sensors and heat sensing devices requires complex methodologies to compensate for general temperature variations which are not as efficient as the present invention. Accordingly, there exists a need for an electronic control circuit that protects the system power supply from short-circuit or excess current conditions without requiring the use of an active current sensing device or heat sensing device.
SUMMARY OF THE INVENTION
The present invention is directed to an electronic circuit that protects a system power supply from being potentially damaged by short-circuit or excessive current situations. The electronic circuit is disposed between the system power supply and the load device to which the system power supply is intended to provide power. Though the load device can be any type of device that requires power from a system power supply, the preferred embodiment of this invention assumes that the load device is part of an automobile system, and the power supply is the automobile's 12-volt battery.
The electronic circuit includes a switch network which initially determines if a load device is connected to the circuit and whether a short-circuit or excess current condition exists. If there is no short-circuit or excess current condition, the switch network permits the system to “power up”. If a short-circuit or excess current condition does exist, the switch network prevents the system power supply from providing power to the system. Thus, the system power supply is protected from possible damage from the short-circuit or excess current condition.
The electronic circuit also includes an output current control circuit for controlling the current provided from the power supply during normal operation and for cutting off the power supply if a short-circuit or excess current condition is detected during operation. In the preferred embodiment, the output current control circuit includes a bi-polar junction output transistor connected between the system power supply and the load device. The output current of the output transistor depends upon a drive current control signal, which is the output of a drive current control circuit. Preferably, the drive current control circuit includes a pre-drive transistor, which controls the input current to the base of the output transistor, which in turn dictates the output current supplied to the load device.
During normal operation (i.e., when there is no short-circuit or excess current condition), the pre-drive transistor determines a stable level of output current to deliver to the load device by receiving feedback from the output transistor. It is generally preferred that the output voltage across the load device be compared to a pre-determined reference voltage by an operational amplifier. The output of the operational amplifier provides the feedback to and activates the pre-drive transistor. As the output voltage across the load device approaches the pre-determined reference voltage, the currents through the pre-drive transistor and the output transistor decrease until the output voltage stabilizes.
If a short-circuit or excess current situation occurs, the drive current control signal deactivates the output transistor, cutting off all current flow to the load device. The output transistor remains deactivated until the short-circuit or excess current situation is eliminated, at which time, the switch network reactivates the circuit.
REFERENCES:
patent: 5698973 (1997-12-01), Goerke et al.
patent: 5831471 (1998-11-01), Nakajima et al.
patent: 5986902 (1999-11-01), Brkovic et al.
Fritz Todd W.
Handley Edward F.
Eaton Corporation
Laxton Gary L.
Rader & Fishman & Grauer, PLLC
Wong Peter S.
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