0ZCK0050FF2E Polymeric PTC Resettable Fuse 6V 500 mA Ih Surface Mount Integrated Circuits

Type 0ZCK Series

PTC’s – Basic Theory of Operation / “Tripped” Resistance Explanation

A Bel PTC consists of a block of polymeric material containing conductive carbon granules which

issandwiched between two conductive metal plates. When this polymer block reaches approximately

125C,either due to current passing through it via conductive chains of carbon particles or due to an

external heatsource; it swells volumetrically. This expansion breaks apart a majority of the chains of

carbon granules thatrun randomly between the two conductive plates. This behavior results in a sharp

increase in resistanceacross the two plates which all but eliminates current flow through the device,

allowing just enough residualcurrent flow to maintain the block’s internal temperature at 125C. Once this

“tripped” state current is cut off,the polymer brick cools and shrinks to its original size, thereby allowing

its broken carbon chains toreestablish themselves and permit the part to return to its low resistance state.

Once cooled to roomambient, the PTC will once again exhibit a resistance less than its “R1max” rating.

At currents below the device IHOLD rating, AND at temperatures below 100C, the PTC maintains

aresistance value below its R1 MAX rating.

The catalog data for each device specifies a "Typical Power"value. This is the power required to exactly

match the heat lost by the tripped device to its ambient surroundings at 23C. By Ohm's Law, power can

bestated as: W = E²/R. Thus the approximate resistance of a “Tripped” PTC can be determined by:

R = E²/W,where "E" is the voltage appearing across the PTC.(usually the supply's open circuit voltage),

and "W" is theTypical Power value for the particular PTC.

Since the PPTC acts to maintain a constant internal temperature, its apparent resistance will change

basedupon applied voltage and, to a lesser degree, ambient conditions. Consider the following example....

A PTC with a Typical Power of 1 watt protecting a circuit using a 60V supply will demonstrate an apparent,

tripped resistance "R" of:R = 60²/1 = 3,600 ohmsThis same tripped device when used to protect a 12V

circuit would now present an apparent resistance of:R = 12²/1 = 144 ohmsThe value for Typical Power is

"typical" because any physical factors that affect heat loss (such as ambienttemperature or air convection)

will somewhat alter the level of power that the PTC needs to maintain itsinternal temperature. In short,

PTCs do not exhibit a constant, quantifiable tripped resistance value.

Operating (Hold Current) Range

100mA - 1.1A

Product Features

- 0805 Chip Size, Fast Trip Time, Low DCR Resistance

- Full compliance with EU Directive 2011/65/EU and amending directive 2015/863

- AEC-Q Compliant - Meets Bel automotive qualification*

* - Largely based on internal AEC-Q test plan

Maximum Voltage

6 - 24V (per table)

Temperature Range 

-40°C to 85° C

Agency Approval

TUV (Std. EN/IEC 60738-1-1 and EN/IEC 60730-1, Cert. R50102117 &R50102187)

UL Recognized Component (Std. UL1434, File E305051)