What is the maximum ambient temperature where PolySwitch devices can be used?
This depends on the product family in question. For the operational state of most of our products the usable range extends up to 85℃ ambient. For some product families (some TD, Chip, AHR, and RHE devices) this can be as high as 125℃ ambient and for some others (VTP) this is as low as 70℃ ambient. For a non-operational state some of our devices (SMD, miniSMD, TS) will withstand solder reflow temperatures for short duration. Use of the device above the temperature rating of the device may cause it to nuisance trip.
What does -2 at the end of a PolySwitch part number mean?
The -2 indicates that the part is supplied in a tape-and-reel packaging format.
What does -1 at the end of a PolySwitch part number mean?
The -1 at the end of a part number designates a radial-leaded device with a 1" long lead. Refer to the product specification drawing for additional dimension details.
What are the UL, CSA or T? file numbers for PolySwitch devices?
See the Raychem Circuit Protection Databook for file numbers for each product family.
What is the composition of the coating on PolySwitch devices?
For R-line and TR parts this is a flame retarded epoxy. For strap devices it is a polyester tape. These materials meet either UL94V-0 or IEC695-2-2 requirements.
What is the performance of PolySwitch devices in a space environment?
PolySwitch devices have not been qualified and are therefore not recommended for a space environment. If the devices are used in a vacuum environment, the thermal transfer component and the electrical performance of the device is affected.
How many times can you trip a PolySwitch device at the maximum voltage and interrupt currents?
Each PolySwitch device is rated to handle a specified operating voltage. Each device can withstand a specified interrupt current as a fault event. To obtain UL recognition, the device must be tripped at least 6,000 times and still exhibit PTC characteristics. Telecom devices have a rating for maximum interrupt voltage for specific fault events that can occur in telecom applications. This may be as few as ten times or as many as several hundred times with the device still meeting the original specification values. Designers should keep in mind that the PolySwitch device is intended to protect against faults and is not intended to be used in applications where it will be expected to be in tripped state as the normal mode of functioning. As stated in the Databook, these devices left in the tripped state can result in device damage, arcing and flame.
What is the failure mode of a PolySwitch device?
The typical failure mode of the device is to fail in a high resistance state. This means that the device does not return to its original low resistance value such that it can maintain the original specified hold current. In order to achieve UL recognition, the device must meet two criteria: (1) be tripped 6,000 times and still exhibit PTC behavior and; (2) stay in a tripped state for over 1,000 hours while exhibiting PTC behavior. If a device is subjected to fault events that exceed its rated voltage and current, or extended for multiple trip events which exceed UL test requirements, the device can exhibit arcing and flame.
What are the effects of potting a PolySwitch device?
In general, potting is not a recommended practice. Although some customers have successfully potted our components, care must be exercised with the material selected for potting as well as with the means of curing the potting material. If the potting material is too rigid it will not allow the PPTC device to expand as designed and therefore will prevent the device from operating as intended. Even if the material is a "soft" potting compound, the thermal transfer characteristics of the device will be affected and the device will perform differently than as specified.
Can PolySwitch devices be bent?
Care should be exercised when forming the leads of any electronic device. With radial leaded products, the leads can be successfully formed without affecting device performance. With battery strap products this is not a recommended practice unless the lead forming is performed at a sufficient distance from the PTC chip so that potential shorts or chip damage is minimized.
What are the effects of pressure on a PolySwitch device?
Pressure on the device will affect the electrical performance of the device. If the pressure is sufficient to restrict the expansion of the device during a trip event then the device will fail to function as specified and could result in device damage. Care should be taken to avoid mounting the device in a configuration that constrains the expansion.
Can PolySwitch devices be used in series?
For most applications there is no benefit, since this is not practical. Putting two PolySwitch devices in series will not double the voltage rating. Because one PolySwitch device will always trip first, the other device will provide no additional protection for the circuit.
Can PolySwitch devices be used in parallel?
Yes, the main benefit is a higher hold current with lower resistance. Refer to the technical overview of PPTC devices in the Databook.
Can a PolySwitch device be cleaned?
Many common solvents used for electrical components are acceptable for cleaning. However some solvents can adversely affect device performance. See the Databook for further information pertaining to a specific device and family.
Is the PolySwitch device self-resetting? How? How fast?
The device resets once the fault and power are cleared. This cuts the trickle current (maintain current), allows cooling which causes the device to contract and reconnect the carbon black particles, thus lowering the resistance. This should not be confused with a bi-metallic device which will self-reset. A typical bi-metallic device will reset even if the fault is not removed, thus causing cycling on and off between the fault event and a protected state which may damage the equipment. The PolySwitch device will latch at the high resistance state until the fault is removed.
By combining the PolySwitch device in parallel with another PTC device such as a light bulb it is possible to design a circuit using a PolySwitch device that may reset without powering off the device. (Refer to the speaker application note in the Databook for an example.)
There are conditions in which a PolySwitch device will self-reset, when the fault is removed and the power is still on. Refer to the current Raychem Circuit Protection Databook section titled "Automatic reset conditions" for more details.