Bel Fuse 0ZRA1200FF1A

A Bel PTC consists of a block of polymeric material containing conductive carbon particles, sandwiched between two conductive metal plates. When the polymer block reaches approximately 125°C — whether due to current flowing through the conductive chains of carbon particles or an external heat source — it undergoes volumetric expansion. This expansion disrupts most of the randomly distributed carbon particle chains between the two conductive plates. This behavior causes a dramatic increase in resistance between the two plates, nearly eliminating current flow through the device, allowing only enough residual current to maintain the internal block temperature at 125°C. Once current is interrupted in this "tripped" state, the polymer block cools and contracts back to its original dimensions, reconnecting the broken carbon chains and restoring the component to its low-resistance state. After cooling to room temperature, the PTC's resistance will again fall below its "R1max" rated value. At currents below the device's IHOLD rating and at temperatures below 100°C, the PTC's resistance remains below its R1 MAX rated value. The catalog data for each device specifies a "typical power" value. This is the power at 23°C at which a tripped device dissipates heat to the surrounding environment in exact equilibrium. By Ohm's Law, power can be expressed as: W = E² / R. Therefore, the approximate resistance of a tripped PTC can be determined by: R = E² / W, where "E" is the voltage across the PTC (typically the open-circuit voltage of the power supply) and "W" is the typical power value for the specific PTC. Since the function of a PPTC is to maintain a constant internal temperature, its apparent resistance will vary with the applied voltage and, to a lesser extent, with ambient conditions. Consider the following example... A PTC with a typical power of 1 watt protecting a circuit powered by a 60V supply has an apparent resistance "R" in the tripped state of: R = 60² / 1 = 3600 ohms When this same tripped device is used to protect a 12V circuit, its apparent resistance is: R = 12² / 1 = 144 ohms The typical power value is "typical" because any physical factor affecting heat dissipation — such as ambient temperature or air convection — will alter to some degree the power level required for the PTC to maintain its internal temperature. In short, a PTC does not exhibit a constant, quantifiable tripped resistance value.

• Extremely high hold current, low DC resistance
• Fully compliant with EU Directive 2011/65/EU and amendment Directive 2015/863
• AEC-Q compliant
• Bel automotive qualified
• Operating (hold current) range: 3A - 14A
• Maximum voltage: 16VDC
• Temperature range: -40°C ~ 85°C