How it works
A resistor converts electrical energy into heat, but damage is not controlled by average watts alone. Under continuous high voltage, electric-field stress, resistor geometry, surface conditions and voltage coefficient can matter even when heating is modest. A brief pulse adds a different problem: energy can concentrate in a small part of the resistive path before heat spreads. Manufacturers therefore specify working-voltage limits and pulse curves or tests separately. Pulse height, duration, shape, repetition and resistance value all matter. Purpose-designed high-voltage and surge series are useful directions, but the correct choice depends on the actual waveform and failure criterion.
The element may be a printed film, a deposited thin film, a metal alloy strip or a wire. Material and geometry set resistance.
Parameters that matter
- Continuous working voltage
- The sustained voltage limit, checked separately from √(PallowedR). (Vdc or Vac rms as specified)
- Voltage coefficient
- Resistance change with applied voltage; particularly relevant to high-voltage measurement accuracy. (ppm/V)
- Pulse waveform
- Peak, duration and shape of the actual stress; a single joule value is not enough. (V or A, µs/ms, rise/fall time)
- Repetition and average power
- How much cooling occurs between pulses and what average heat accumulates. (Hz, duty %, W)
- Pulse acceptance and insulation
- Allowed post-stress drift or failure condition, plus board-level spacing and surface requirements. (ΔR%, pulse count, clearance mm)
A worked selection example
Illustrative calculation · not a product guarantee
A power-safe resistor can still exceed its voltage limit
Assume 400 Vdc across 1 MΩ. A hypothetical resistor allows 0.25 W under the actual thermal conditions but only 200 V continuous working voltage.
- Power = 400² / 1,000,000 = 0.16 W.
- 0.16 W is below 0.25 W, but 400 V exceeds the assumed 200 V limit, so this candidate fails.
- An illustrative four-part series chain of 250 kΩ each has 100 V and 0.04 W per resistor under ideal equal sharing.
- Check tolerance, voltage coefficient, PCB spacing and unequal transient sharing before approving a chain.
- For a separate rectangular-pulse example, 100 V across 1 kΩ for 0.1 ms gives 10 W peak and 1 mJ. At 1 kHz repetition, average power is 1 W; all three constraints still need checking.
Keep continuous voltage, peak pulse stress and average heating as separate rows on the comparison sheet.
Where it fits
Suitable starting points
- High-voltage measurement dividers with adequate voltage coefficient
- Surge, startup or discharge duties supported by pulse data
- Snubber and transient paths when parasitics and waveform are validated
Where to take extra care
- Using short-time overload voltage as a continuous rating
- Selecting by energy alone
- Calling a resistor fusible or a protective device without the specific qualification
Series directions to investigate
Dedicated high-voltage chips, long-body resistors, pulse-rated chips and power packages serve different jobs. Vishay RCV and D/CRCW-IF illustrate separate families. Fenghua RA is listed as an anti-surge family; request the correct high-voltage document separately.
What Chinese suppliers can offer
Where the opportunity lies
Fenghua's official catalogue includes dedicated stress-oriented resistor directions and a retrievable RA anti-surge specification, providing an evidence-based starting point for domestic pulse candidates.
What still needs evidence
The catalogue link labelled High Voltage currently opens an Anti-Surge RA document. Treat that mismatch as unresolved; do not claim a verified high-voltage rating from the heading. Require the correct exact-part document and waveform review.
Questions for the supplier
- 01
What continuous working voltage applies to this exact resistance and package?
- 02
Please review our waveform, including peak, duration, repetition, temperature and allowed drift.
- 03
Which pulse curve or test covers the proposed resistance, and is it single-shot or repetitive?
- 04
What voltage coefficient, spacing guidance and coating conditions apply?
- 05
If proposing a substitute, can you provide the exact series datasheet rather than a similarly named catalogue page?
Technical references
These references support the principles and catalogue directions discussed here. Public documentation is a different evidence level from a supplier reply, a lot document or an independent test. This guide does not claim those later stages have been completed.
- 1. RCV High Voltage Thick Film Chip Resistors
- 2. D/CRCW-IF Pulse Proof Thick Film Chip Resistors
- 3. Pulse Capabilities for Thick Film Power Resistors
- 4. Thick Film Resistors catalogue
- 5. RA Anti-Surge Thick Film Chip Fixed Resistors, revision 10.0
- 6. TH Thin Film Chip Fixed Resistors, revision 12.0
These guides explain selection principles. Final decisions require the current datasheet for the exact ordering code, operating conditions and appropriate application testing.