Resistor max ratings

Great question! Yes—the ratings and operating limits you need to check depend on whether the resistor is used with DC, AC, PWM, or pulses. For PWM, it helps to distinguish average power dissipation from the voltage and power during the ON interval.

Some resistors can handle peak voltages or instantaneous power levels above their continuous-operation ratings, provided the manufacturer’s specified pulse conditions are met. The permitted limits are defined by the particular resistor’s pulse specifications.

Vishay’s application note explains these limits in detail:
https://www.vishay.com/docs/28870/pulseloadsmdlimit.pdf

For example, consider an ideal rectangular PWM waveform applied across a 10 kΩ resistor, with 100 V during the ON interval and 0 V during the OFF interval. At a 10% duty cycle:

• Power during the ON interval: 100² ÷ 10,000 = 1 W
• Average power: 1 W × 0.1 = 0.1 W

If the resistor is rated to dissipate 0.25 W under the actual temperature and mounting conditions, the average power of 0.1 W is within that limit. The next step is to check whether 100 V and 1 W during each ON interval fall within the resistor’s repetitive-pulse limits.

When reading the datasheet, check these three things together:

1. Rated Power
Compare the average power dissipation with the allowable power, accounting for temperature and mounting conditions.

2. Voltage Ratings
Distinguish the continuous working-voltage limit from the permitted pulse voltage. Maximum Overload Voltage is defined under specific overload-test conditions; for repetitive PWM operation, use the manufacturer’s applicable repetitive-pulse voltage limits.

ROHM explains rated voltage, maximum element voltage, and maximum overload voltage here:
https://techweb.rohm.com/product/passive-components/resistors/23749/

3. Repetitive-Pulse Capability
Check the temperature and other conditions specified for the pulse-load curves, then verify that the pulse power, pulse duration, and repetition frequency are within the permitted range.

Vishay’s pulse-load checklist provides a practical guide:
https://www.vishay.com/docs/48516/_ms9702509-2401-vishaychecklistpulseload.pdf

For the same resistor and peak voltage, reducing the duty cycle reduces average power dissipation. The permitted peak voltage is determined separately by the pulse specifications, including pulse duration and repetition conditions. Even at the same duty cycle, changing the frequency changes the pulse duration, so duty cycle and frequency should be considered together.

Thank you for the question!