Polytronics-(PPTC)pptc and resettable fuse and overcurrent protection company-products

DSC Application Note

Why do we need over-current protection on the DC-IN side?

To ensure the reliability of the power in-put system, most of the designers will choose to put a power protection device in serial on the DC-IN side to prevent the main system being damaged by any over-current event once the power supply fault. Now, PPTC is often used in the secondary side of power supply system.

Example:

In Figure 1, there is a typical circuitry for the power system of a digital camera. In this example, three over-current protection devices (PPTC, Polymeric Positive Temperature Coefficient Resistor ) are being used for the better reliability of the power system. Three of these PPTC devices are served as different function.

®To ensure the reliability of the system, a PPTC is required on the system side to trip and to block the over-current occurred in the main system or power system.

®Once the failure of insulation or thermal runaway happened to the flash light transformer, the circuitry current will be suddenly increased by many fold. PPTC is required to limit the over-current to the flash light circuitry to prevent the related devices from damaging.

®The PPTC can also be used in the battery pack to serve as an over-current, overcharge, and over-temperature protection to prevent the fault to the batteries and to guarantee the users’ safety.

Product Selection

Table 1
Application	Operation voltage	Operation current	PPTC part number	The most popular part
DC-in side	3V ~ 8V	1A ~ 2A	SMD1206P150TS SMD1812P150TS SMD1812P160TS SMD1812P200TS SMD1812P260TS	SMD1206P150TS
Flash light circuitry	3V ~ 24V	0.5A ~1A	SMD1206P075TS SMD1206P100TS SMD1210P075TS SMD1210P110TS SMD1812P075TS SMD1812P075TS/24 SMD1812P110TS SMD1812P110TS/16	SMD1206P100TS SMD1210P110TS
Battery pack	3V ~ 24V	0.7A ~ 4.2A	STD,VTD,LTD,VLD	VTD

The advantages of Everfuse^TM(PPTC)

®Comparing to traditional one time fuse, the resettable function for Everfuse will lower the maintenance and service cost to the electronic product manufacturer.

®The time to trip for Everfuse is similar to slow blow type fuses with slower reaction time. Therefore, it is not necessary to consider the safety margin in contrast with the fast acting fuses.

®Different form factors available (SMD, RLD, and Strap type) with various footprint and current rating to meet the customers’ need.

Note:

®Everfuse^TM: the trade mark of the products of Polytronics Technology Corp.

®PPTC: Polymeric Positive Temperature Coefficient Resistor