PTCs for motor protection, circuit protection and self-limiting heating elements
Motor PTC thermistors and SMD PTCs, SKTY linear PTCs,
PTC heating elements and PTC current fuses are all
available from the UK's market leaders.
ATC Semitec Products
• NTC Thermistors • PTC Thermistors • Temperature Sensors • Platinum Sensors/Pt100s • Thermostats/Thermal Cutouts • Disc Thermostats • Precision Thermostats • Adjustable Thermostats • Thermal Fuses • PTC Resettable Fuses • Circuit Protection Devices
A full range of motor protection PTC thermistors with temperature switch points from 60°C to 190°C in 10K steps. At its thermal switching point (Ts), the PTC resistance increases dramatically from a few hundred to several thousand ohms over several degrees. Thus the PTC acts as a solid-state thermal switch and can be used to trigger an electronic circuit to switch off an over-loaded electric motor, bearing, or appliance.
Colour-coded 26AWG PTFE leads ensure compliance to the DIN44081 standard and 3-phase motor triplet versions to DIN44082. Owing to their very low cold impedance and step-function PTC characteristic, several motor protection PTCs can be wired in series so that multiple points (i.e. 2 to 3 motor phases) can be monitored at the same time - any one over-temperature condition triggering a motor protection relay circuit and thus thermally protecting the motor.
Motor Protection PTCs - PDF document
Motor Protection Thermal Cut-outs - PDF document
The TPM series of SMD PTC thermistors are frequently used as thermal switches in electronic circuits. Their small size (0402, 0603 or 0805) and step change RT curve (at the trip point) makes these solid-state temperature switches ideal for small spaces and simple to incorporate electronically. Temperature switch points from 65°C to 135°C are available with several R25 (resistance at 25°C) values to suit varying circuit conditions.
SMD PTC Thermistors - PDF document
Ceramic PTC thermistors are often used as re-settable current fuses as they can offer several benefits over conventional fuses. Over-voltage or over-current conditions cause the PTC protector to "switch" from a low resistance to a high resistance state, effectively limiting (i.e. switching off) the through current. The PTC current fuse thus protects the circuit, appliance or load that is in series with it.
Often simpler to incorporate in a circuit than a current fuse, PTC fuses also don't need replacing and thus help to minimise service calls where nuisance tripping is caused by transient surges.
270V Ceramic PTC Fuses - PDF document
Semifuse Polymer PTCs - More info on the PTC fuses page
The SKTY series of linear PTC elements offers a solution for the once common KTY series sensors. SKTY PTC elements are mounted on a small 3mm x 6mm p.c.b. and are available with R25 values of 1kohm and 2kohm with ±1% tolerances.
• More info on the Platinum Sensor/Linear PTC page
By applying a voltage across a PTC thermistor, current will flow and begin to heat the PTC. The PTC element rises in temperature until it reaches its Curie point, when its resistance will start to rise dramatically.
The increase in PTC resistance limits the through current until the PTC heater reaches a state of equilibrium. If heat is withdrawn from the PTC, its resistance will drop allowing more current to flow through the PTC until a steady-state condition is reached again. Conversely, if the PTC element temperature rises, its resistance will increase accordingly reducing the through current until a further state of equilibrium is achieved.
Thus a PTC thermistor can operate as a self-regulating heater.
Circular Disc PTC Elements - PDF document
Rectangular PTC Elements - PDF document