Heater with PTC element an buss system

Details Heater with PTC element an buss system Heater with PTC element an buss system

2000-05-25

2001-10-23

Walberg, Teresa (Department: 3742)

Electric heating

Heating devices

With power supply and voltage or current regulation or...

C219S541000

Reexamination Certificate

active

06307188

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention pertains to a heater pad with a PTC (positive temperature coefficient) element and a buss system to equalize the current path distances.
2. Description of the Prior Art
In the prior art, PTC (positive temperature coefficient) heaters, such as those disclosed in U.S. Pat. Nos. 4,857,711 and 4,931,627 to Watts, have a resistance which increases in response to increasing temperatures. This fundamentally reduces thermal energy output in view of a substantially constant voltage applied across this resistance, thereby tending to prevent overheating, and is therefore useful in applications with varying ambient temperatures, such as automotive mirror defrosting. Users in several applications desire a heater with both terminals across a single face of the heater in order to simplify electrical connections and to accommodate standard electrical circuitry. However, such a configuration often results in uneven resistance through the various electrical paths thereby resulting in uneven heating across the heating surface, increased current draw, and increased buss width requirements.
OBJECTS AND SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide a heater with PTC (positive temperature coefficient) characteristics which has relatively uniform heating characteristics across its heating surface.
It is therefore a still further object of this invention to provide heater with PTC characteristics which has relatively uniform resistance through the various electrical paths of its heating surface.
It is therefore a still further object of this invention to provide a heater with PTC characteristics which has a reduced current draw.
It is therefore a still further object of this invention to provide a heater with PTC characteristics which has reduced requirements with respect to main buss width.
It is therefore a still further object of this invention to provide a heater with PTC characteristics which has electrical terminals across a single face in order to accommodate standard electrical connections.
These and other objects are attained by providing a heater with a feeder buss layer formed on a polyester substrate. The feeder buss layer includes conducting portions which provide electrical communication from the terminals through conducting conduits in two diagonally opposed corners in an adjacent dielectric layer. The conducting conduits are further in electrical communication with diagonally opposed corners of an adjacent main buss layer (otherwise known as a PTC conductor layer). The main buss layer provides current to the adjacent PTC thermistor layer. An adhesive layer may be formed adjacent to the PTC thermistor layer to provide electrical insulation and to provide the ability to fasten the heater to an adjacent surface, such as an automotive mirror.


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