Two-terminal transistor PTC circuit protection devices

Details Two-terminal transistor PTC circuit protection devices Two-terminal transistor PTC circuit protection devices

1998-10-22

2001-02-13

Leja, Ronald W. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

Circuit interruption by thermal sensing

C361S058000

Reexamination Certificate

active

06188556

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention generally relates to electronic circuits, and more particularly to circuit protection devices comprising a resistor with a positive temperature coefficient (PTC), referred to as PTC_r, operating in combination with a semiconductor device.
PTC_r circuit protection devices are well known. The device is placed in series with a load, and under normal operating conditions, is in a low temperature, low resistance state. However, if the current through the PTC_r device increases excessively, and/or the ambient temperature around the PTC_r device increases excessively, then the PTC_r device will be “tripped,” i.e., converted to a high resistance state such that the current is reduced substantially to a safe level. Generally, the PTC_r device will remain in the tripped state, even if the fault is removed, until the device has been disconnected from the power source and allowed to cool. After the current and/or temperature return to their normal levels, the PTC_r device will switch back to the low temperature, low resistance state.
An example of a PTC_r device is one that contains a PTC_r composition which is composed of a PTC conductive polymer. The largest steady state current which will not cause any of the devices in a batch of devices to trip is referred to as the “hold current” (I
hold
), and the smallest steady state current which will cause all of the devices to trip is referred to as the “trip current” (I
trip
). In general, the difference between I
hold
and I
trip
decreases slowly as the ambient temperature increases, and the higher the ambient temperature, the lower the hold current and the trip current.
PTC and semiconductor devices have been used together in electrical circuits. In some instances the PTC_r devices have been used to protect the semiconductor devices from overcurrent and/or overtemperature conditions. In other instances, the semiconductor and PTC_r devices have been used together to protect the circuits in which they reside from overcurrent and/or overvoltage conditions. In most cases, the PTC_r device is operated at its normal current and generally has a large size. The PTC_r devices of large size are not suitable for portable electronic devices to which size and weight are important. PTC_r devices of large size are also not suitable for high density electronics circuits.
It is desirable to reduce the size of the PTC_r circuit protection devices to allow them to be more suitably used in portable electronic devices and high density electronic circuits.
SUMMARY OF THE INVENTION
The present invention provides a circuit protection device that has a reduced size and weight and is particularly suitable for use, for example, in portable electronic devices and high density electronic circuits. According to one embodiment of the present invention, a circuit protection device comprises a positive coefficient temperature (PTC) element, and a bipolar junction transistor having base, collector, and emitter terminals. The PTC element is connected between the base and collector terminals of the transistor. The PTC element may be thermally coupled to the transistor and packaged with the transistor as a hybrid device. An electrical load may be connected to the collector terminal of the transistor. In a first embodiment of the invention, the transistor is of NPN type. In a second embodiment of the invention, the transistor is of PNP type.
According to another embodiment of the present invention, a circuit protection device comprises a PTC element and a Darlington circuit having base, collector and emitter terminals. The PTC element is electrically connected between the base and collector terminals of the Darlington circuit. The PTC element may be thermally coupled to the Darlington circuit and packaged with the Darlington circuit as a hybrid device. An electrical load may be connected to the collector terminal of the Darlington circuit. In a third embodiment of the invention, the Darlington circuit comprises two NPN type bipolar transistors. In a fourth embodiment of the invention, the Darlington circuit comprises two PNP type bipolar transistors.
Fifth and sixth embodiments of the invention are variations of the third and fourth embodiments. In each of the fifth and sixth embodiments of the invention, the Darlington circuit is a complementary Darlington circuit and comprises an NPN type bipolar transistor and a PNP type transistor.
A method for protecting an electrical load, according to the present invention, is also disclosed.
Other objects and attainments together with a fuller understanding of the invention will become apparent and appreciated by referring to the following description and claims taken in conjunction with the accompanying drawings.


REFERENCES:
patent: 3708720 (1973-01-01), Whitney et al.
patent: 3884080 (1975-05-01), Chapman
patent: 4041276 (1977-08-01), Schwarz et al.
patent: 4281358 (1981-07-01), Plouffe et al.
patent: 4295088 (1981-10-01), Malchow
patent: 5381296 (1995-01-01), Ekelund et al.
patent: 5684663 (1997-11-01), Mitter
patent: 5763929 (1998-06-01), Iwata
patent: 2249463 (1975-05-01), None
patent: WO 94/11937 (1994-05-01), None
International Search Report for International Application No. PCT/US99/24716 dated Feb. 18, 2000.

Affiliated with

Also associated with

Rating

Two-terminal transistor PTC circuit protection devices does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Two-terminal transistor PTC circuit protection devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Two-terminal transistor PTC circuit protection devices will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2612828