How to Derate Voltage-Sensitive Resistors [metal Oxide Varistors]
Varistor Power-Derating Curve
This style of Varistor is rated to operated out to at +85oC before any derating is required. However above 85C the power must be reduced as the varistor temperature increases. A derating chart is often used, with derating starting at 25oC. Since parameters are application dependent, power de-rating curves or charts should be considered general rather than absolute, and only used as a guideline. The safest designs use the largest physical size operating at conservative temperatures and power ratings. The minimum power dissipation for this style varistor occurs at 125 degrees centigrade.
Varistor Dimensions / Varistor Component Outline
Power rating. The average power dissipation rating applicable to parts covered by this specification is1.0 W at 85OC. For varistors operated at ambient temperatures in excess of 85C, the voltage shall be derated in accordance to the derating curve shown above.
