Thermistors Essay

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PTC Thermistors
There are three types of PTC or positive temperature coefficient thermistors.
• Ceramic Switching PTC Thermistors
• Silistor Silicon PTC Thermistors
• Polymer PPTC Thermistors
Change in the resistance of a PTC thermistor can be brought about either by a change in the ambient temperature or internally by self-heating resulting from current flowing through the device.

Manufacturing process
The manufacturing process for PTC thermistors begins by mixing selected material with a binding agent. Next; the mixture is pressed and sintered into wafer form. The mix of raw material will vary depending on the specific type of PTC thermistor being manufactured
General PTC Thermistor Applications
• Time Delay
• Degaussing
• Motor Starting
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Because they possess positive coefficient characteristics, they exhibit a trace amount of negative temperature coefficient until they reach a critical temperature point known as a “curie” or transition state. At which point, the device begins to exhibit a positive temperature coefficient along with a significant increase in resistance.
Manufacturing Material
Ceramic Switching PTC thermistors are made from a polycrystalline ceramic material that contains barium titanate. This mix of material when doped with rare earth metals is what gives them their positive temperature coefficient characteristics.
Applications
• Over-current protection:
• Time Delay:
Benefits
To demonstrate the versatility of the PTC thermistor; below are some examples where their use as an Inrush Current Limiter is the optimal choice.
• Ambient temperature is greater than 65 °C.
• Ambient temperature is less than Zero °C.
• Reset time needs to be near zero °C.
• Short circuit concerns.
Configurations
• Radial Leaded
• Surface Mount

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