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| 一、Characteristics of polymer PTC |
１. Basic principle：
Polymer PTC is a matrix of polymer and conductive particles. With the suitable mixing process, the conductive particles form conductive chains. When the current is below Itrip, the device's resistance is very low. But when the device is over currented, the heat will generate, disrupting those conductive chains, and the device's resistance will be high. With the removal of the over current, the volume of the device will decreases, the conductive chains will restore, and the resistance will be low again. So the polymer PTC is also named Polymer Resettable Fuse. |
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The relationship of resistance and temperature shows in figure d. At the point a, the heat generated equals the heat dissipated. At the point b, there is also a balance at some higher temperature. When the temperature continues increasing to the point c, a tiny temperature increase will cause the resistance much higher. And the resistance of point d is very high, resisting the current and protecting the electrical devices.
２. How to install：
The Polymer PTC is usually serially connected with other devices and can be used in DC or AC circuits for it's no polarity, shows in 图E. |
二. Performance and characteristics
1. The low initial resistance: When the device is at normal working condition, the resistance is low and the surface temperature is also low.
2. The short time to trip: For its own characteristics, the PTC's trip time is much shorter than other protection devices.
3. Self-operation: When the PTC device is tripped, the current is very low and the resistance is very high. Only after the current is removed, the resistance will be low again.
4. Resettable: When the over current is removed, the PTC devices will reset and there is no need to replace it. So it is also called resettable fuse.
5. The maximum current: The polymer PTC can resist very high current, some types can resist 100Amps.
三. The typical application and how to select
１. The typical application
The polymer PTC can be used in a wide range, including electrical devices, telecom products, electric power devices and etc. For example, VCDs, speakers, acoustics, computer equipments, battery charger, energy-saving bulbs and etc.
２. How to select
(1) Make sure the maximum voltage.
(2) Make sure the hold current.
(3) Make sure the minimum trip current.
(4) Make sure the maximum fault current.
(5) Select the products based on those above parameters and the figures below.
(6) If the working temperature is far from 25℃, please insult us to select the suitable products. |
4. Introductions
(1)Typical Part Numbering System：
| Mark |
G |
U |
X |
P |
| Vmax |
16V |
30V |
60V |
15V-30V |
(2)Introduction：
IH: Hold Current. Maximum current at which the device will not trip at 25℃ still air. For example, 020 means 0.2amp and 300 means 3amps.
IT: Trip Current. The minimum current at which the device will always trip at 25℃ still air.
Vmax: Maximum Voltage. The maximum voltage that the device can withstand.
Imax: Maximum current. The maximum current that the device withstand.
Pdtyp: Power dissipated. The power dissipated in tripped state at 25℃ still air environment.
Ttrip：tipe time. the maximum trip time at 5 * Lh
Rmin: Minimum resistance. The minimum resistance when the device is not tripped at 25℃ still air environment
Rmax: Maximum resistance. The maximum resistance when the device is not tripped at 25℃ still air environment |
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