A chip resistor has two voltage limits, and the one that binds is usually not the one
calculated from power. Walsin Technology (Walsin) defines Rated Continuous Working Voltage
as the square root of rated power times resistance, or the maximum operating voltage
tabulated for the case size, whichever is lower. Above a certain resistance the table wins.
What is the voltage rating of a chip resistor?
It is called Max. Operation Voltage in Walsin’s quick reference data, stated as RCWV, Rated
Continuous Working Voltage. It is a hard ceiling per case size: for the general purpose thick
film range, 200 V at 1206, 150 V at 0805, 75 V at 0603 and 50 V at 0402, DC or RMS.
Max. Overload Voltage sits alongside it at double the operating value: 400 V at 1206, 300 V at
0805, 150 V at 0603 and 100 V at 0402. That is a test level, not a continuous rating.
Both figures come from Walsin_WR_General_Purpose_Chip_Resistor.pdf, the WR approval sheet
held by Venatech Limited, an authorised Walsin distributor in Hong Kong. Walsin’s note on
that page points at IEC publication 60115-8.
Flagged for review. Venatech holds two Walsin chip resistor datasheets as PDFs,
Walsin_WR_General_Purpose_Chip_Resistor.pdfand
Walsin_MR_Automotive_Thick_Film_Chip_Resistor.pdf, and no public URL for either. Confirm
the public datasheet URLs before this post is published.
Why is the voltage limit not just the square root of P times R?
Because Walsin applies both rules and takes the lower answer. The formula in the WR approval
sheet reads: RCWV is the square root of rated power multiplied by resistance value, or the
maximum RCWV listed for the case size, whichever is lower. Engineers calculate the first term
and stop.
Work a 1206 at 1 MΩ. Rated power is 1/4 W, so the square root of 0.25 times 1,000,000 is
500 V. The tabulated maximum operating voltage for a 1206 is 200 V. The part is a 200 V part.
Design it to 500 V and the element is over-stressed two and a half times, with no thermal
symptom.
Work the same 1206 at 10 kΩ. The square root of 0.25 times 10,000 is 50 V. The table allows
200 V. Here the power rule binds and the table is irrelevant. Same case size, same series,
same rated power, and the governing limit has swapped over.
At what resistance does the voltage ceiling start to bind?
At the resistance where the two rules agree, which is the tabulated voltage squared divided by
the rated power. Below that resistance, the power rating governs. Above it, the voltage ceiling
governs and the part can no longer use its full power rating.
| Series and size | Rated power | Max. operation voltage | Crossover resistance | Above crossover, the binding limit is |
|---|---|---|---|---|
| WR, 0402 (1005) | 1/16 W | 50 V | 40 kilohms | voltage ceiling |
| WR, 0603 (1608) | 1/10 W | 75 V | 56.25 kilohms | voltage ceiling |
| WR, 0805 (2012) | 1/8 W | 150 V | 180 kilohms | voltage ceiling |
| WR, 1206 (3216) | 1/4 W | 200 V | 160 kilohms | voltage ceiling |
| MR, 0402 (1005) | 1/10 W | 50 V | 25 kilohms | voltage ceiling |
| MR, 0603 (1608) | 1/8 W | 75 V | 45 kilohms | voltage ceiling |
| MR, 0805 (2012) | 1/4 W | 150 V | 90 kilohms | voltage ceiling |
| MR, 1206 (3216) | 1/4 W | 200 V | 160 kilohms | voltage ceiling |
| MR, 1210 (3225) | 1/2 W | 200 V | 80 kilohms | voltage ceiling |
Crossover resistance is calculated from Walsin’s own two published figures per size, in
Walsin_WR_General_Purpose_Chip_Resistor.pdf and
Walsin_MR_Automotive_Thick_Film_Chip_Resistor.pdf. It is arithmetic, not a specification.
Read the MR rows carefully. The automotive MR parts carry more power in the same case size —
1/4 W at 0805 against 1/8 W for WR — while the voltage ceiling is identical. More power at the
same voltage moves the crossover down, not up: an MR 0805 is voltage-limited above 90 kΩ where
the WR 0805 is voltage-limited above 180 kΩ.
Also, the WR 0805 crossover at 180 kilohms is higher than the WR 1206 crossover at 160
kilohms. Case size does not order the crossover monotonically, so build the table per size.
How many general purpose parts are voltage-limited rather than power-limited?
More than a quarter of them. Venatech holds 234,815 Walsin chip resistor part numbers across
137 parametric exports. Inside the WR general purpose series, in the four case sizes the WR
approval sheet covers, 1,136 of 4,016 parts sit above the crossover.
| Case size | WR general purpose parts held | Crossover resistance | Parts above crossover | Share above crossover |
|---|---|---|---|---|
| 0402 (1005), 1/16 W | 969 | 40 kilohms | 333 | 34.4% |
| 0603 (1608), 1/10 W | 969 | 56.25 kilohms | 310 | 32.0% |
| 0805 (2012), 1/8 W | 969 | 180 kilohms | 243 | 25.1% |
| 1206 (3216), 1/4 W | 1,109 | 160 kilohms | 250 | 22.5% |
| Total | 4,016 | — | 1,136 | 28.3% |
Unique to Venatech’s data. 1,136 of the 4,016 Walsin WR general purpose chip resistors
in the four case sizes the WR approval sheet covers sit above the resistance at which the
tabulated voltage ceiling binds instead of the power rating. That is 28.3% of the range,
rising to 34.4% at 0402. Neither the part number nor the parametric data tells you which
side of the line a part is on. Measured from our extract of Walsin’s own export against
Walsin’s own published voltage table.
WR12X1004FTL is a WR 1206 at 1 MΩ, ±1%, 1/4 W — above the
160 kilohm crossover, so a 200 V part whatever the power maths says. WR12X1002FTL matches it
on series, size, tolerance, TCR and power at 10 kΩ — below the crossover, so a 50 V part
governed by power.
What does the high voltage series actually change?
The voltage ceiling, and nothing else visible in the data. The Thick Film High Voltage Chip
Resistor group is 20,244 parts across five case sizes from 0603 to 2512, and size, resistance,
tolerance, TCR and rated power all overlap with the general purpose range.
| Case size | High voltage parts held | Rated power | Resistance span held |
|---|---|---|---|
| 0603 (1608) | 3,924 | 1/10 W | 47 ohms to 22 megohms |
| 0805 (2012) | 3,966 | 1/8 W | 47 ohms to 51 megohms |
| 1206 (3216) | 4,118 | 1/4 W | 47 ohms to 100 megohms |
| 2010 (5025) | 4,118 | 1/2 W | 47 ohms to 100 megohms |
| 2512 (6432) | 4,118 | 1W | 47 ohms to 100 megohms |
Put a general purpose part and a high voltage part side by side at the same value and almost
every field matches.
| Field | WR12X1004FTL |
WK12V1004FTL |
WF12N1004FTL |
WF12N1004FTLJ |
|---|---|---|---|---|
| Series | Thick Film General Purpose | Thick Film High Voltage | High Voltage, UL Safety Certification | High Voltage, UL Safety Certification (Automotive) |
| Size | 1206 (3216) | 1206 (3216) | 1206 (3216) | 1206 (3216) |
| Resistance | 1 megohm | 1 megohm | 1 megohm | 1 megohm |
| Tolerance | ±1% | ±1% | ±1% | ±1% |
| TCR | within ±100 | within ±100 | within ±100 | within ±100 |
| Rated power | 1/4 W | 1/4 W | 1/4 W | 1/4 W |
| Termination | Sn base, lead free | Sn base, lead free | Sn base, lead free | Sn base, lead free |
| Packaging | 7 inch reel taping | 7 inch reel taping | 7 inch reel taping | 7 inch reel taping |
Match / mismatch vs WR12X1004FTL |
reference | match: size, resistance, tolerance, TCR, power, termination, packaging · mismatch: series, and the voltage rating that goes with it | match: all parametric fields · mismatch: series, UL safety certification | match: all parametric fields · mismatch: series, UL certification, automotive grading, trailing J |
All four part numbers return a row in Walsin’s parametric export.
Flagged for review. Venatech holds no Walsin datasheet for the WK or WF high voltage
series, so we cannot state their maximum operating voltage per case size. The series and the
part numbers are real; the voltage rating must come from Walsin in writing before it is
quoted or published here.
Why can I not find high voltage parts by filtering on voltage?
Because there is no voltage field. Across all 234,815 Walsin chip resistor rows in 137
exports, the columns are Part Number, Series Group, Series, Size, Resistance, Tolerance, TCR,
Rated Power, Packaging and Termination. Ten columns, none of them a voltage.
The one parameter the high voltage series exists to change is the one you cannot search on. The
only way in is to select the series group Thick Film High Voltage Chip Resistor by name. Filter
by resistance, size and power and you get general purpose parts only.
Unique to Venatech’s data. Walsin’s chip resistor parametric export carries no voltage
column anywhere in its 234,815 rows and ten fields. The high voltage series is therefore
unreachable by parametric search on the parameter it is named for; it can only be found by
selecting the series group by name. Counted across all 137 export files we hold.
On cross-reference work, a part specified at 400 V continuous in an 0805 will not be matched by
searching on resistance and size alone. Match at series level first, then at value.
How do I read a Walsin high voltage part number?
Four fields carry meaning: the two-letter prefix, the character in position five, the
tolerance letter, and whether there is a trailing J. WK12V1004FTL is prefix WK, size 12 for
1206, position-five V, resistance code 1004 for 1 MΩ, then F for ±1%.
| Feature | What it indicates in the high voltage group | Parts held |
|---|---|---|
Prefix WK |
non-UL high voltage series | 13,606 |
Prefix WF |
UL series and part of the standard high voltage series | 6,638 |
Position 5 = V |
not UL Safety Certification | 17,240 |
Position 5 = N |
UL Safety Certification series | 3,004 |
Trailing J |
automotive variant of the same base part | see below |
| Embedded space before the tolerance letter | ±5% parts only | 2,657 |
The trailing J catches people. WF12N1004FTL and WF12N1004FTLJ are identical on every field
in Walsin’s export; the J is the only difference.
The embedded space is the other. Every ±5% part in the high voltage group carries a space
before the tolerance letter: WK12V105 JTL, WK25V470 JTL, WF25N107 JTL. That is 2,657 of
the 20,244 parts, none of which resolves if pasted into a BOM line.
Flagged for review. The prefix and position-five coding above is inferred from counting
our extract, not from a published Walsin ordering key. Confirm the decode with Walsin.
Which high voltage series do I need for a UL job?
One of the two UL Safety Certification series. Between them they hold 3,004 parts, split 1,502
and 1,502 across the same five case sizes, and their names differ by nothing except the word
“(Automotive)”. Neither reaches below 100 kilohms, which is the constraint that usually
decides the answer.
| Series | Parts held | Case sizes | Resistance span held | Match / mismatch |
|---|---|---|---|---|
| Thick Film High Voltage Chip Resistor | 10,437 | 0603 to 2512 | 47 ohms to 100 megohms | reference |
| Thick Film High Voltage Chip Resistor (Automotive) | 6,803 | 0603 to 2512 | 47 ohms to 51 megohms | match: sizes · mismatch: no UL, lower ceiling at 51 megohms |
| High Voltage UL Safety Certification | 1,502 | 0603 to 2512 | 100 kilohms to 100 megohms | match: sizes, top of range · mismatch: nothing below 100 kilohms |
| High Voltage UL Safety Certification (Automotive) | 1,502 | 0603 to 2512 | 100 kilohms to 100 megohms | match: sizes, range, counts · mismatch: automotive grading, trailing J |
Unique to Venatech’s data. Walsin lists 20,244 high voltage chip resistors, of which
3,004 sit in two UL Safety Certification series whose names differ only by the word
“(Automotive)” — 1,502 parts each, with matching case size distributions and part numbers
separated only by a trailing J. Neither series holds anything below 100 kilohms. Counted
from our extract.
If a UL-certified high voltage part is needed below 100 kΩ, changing case size will not fix it;
the requirement has to go back to Walsin. Surge withstand is a separate axis: a high voltage
part is not automatically surge-tolerant.
FAQ
What is RCWV on a chip resistor datasheet?
RCWV is Rated Continuous Working Voltage. Walsin defines it as the square root of rated power
multiplied by resistance value, or the maximum RCWV tabulated for the case size, whichever is
lower. The second term is the one designers skip, and it is the one that governs at higher
resistances.
What is the maximum voltage on a Walsin 1206 chip resistor?
200 V DC or RMS continuous for the WR general purpose and MR automotive thick film series,
with a 400 V maximum overload figure used for test purposes only. At 1206 the crossover is
160 kilohms: below it the 1/4 W power rating governs, above it the 200 V ceiling governs.
Why does my 1 megohm 1206 resistor not handle 500 V?
Because the power calculation gives 500 V but the tabulated maximum operating voltage for a
1206 is 200 V, and Walsin’s rule takes the lower of the two. The element, not the package,
sets the ceiling. Running it at 500 V continuous over-stresses the resistive layer with no
thermal warning.
How do I know if my resistor is voltage-limited or power-limited?
Divide the tabulated maximum operating voltage by itself and then by the rated power: the
voltage squared over the power gives the crossover resistance. Above that resistance the part
is voltage-limited and cannot use its full power rating. Below it, the power rating governs
and the voltage ceiling is slack.
What is a high voltage chip resistor?
It is a thick film chip resistor built to carry a higher continuous working voltage than the
general purpose part in the same case size, usually by lengthening or serpentining the
resistive element. Walsin lists 20,244 of them in five case sizes from 0603 to 2512, at the
same rated power as the general purpose parts.
Can I search Walsin’s tool for a resistor by voltage?
No. Walsin’s chip resistor parametric data carries no voltage column in any of the 137 export
files Venatech holds, across 234,815 rows. The high voltage range can only be reached by
selecting the series group by name, which is why it is easy to miss entirely.
What does a trailing J mean on a Walsin chip resistor part number?
In the high voltage group it marks the automotive variant of the same base part.
WF12N1004FTL and WF12N1004FTLJ match on size, resistance, tolerance, TCR, rated power,
termination and packaging, and sit in two series whose names differ only by the word
“(Automotive)”. The J is the only difference in the number.
Why will some Walsin part numbers not paste into my BOM?
Because they contain an embedded space. Every ±5% part in Walsin’s high voltage chip resistor
group carries a space before the tolerance letter, as in WK12V105 JTL — 2,657 of the 20,244
parts. Pasted into a BOM field or a search box unmodified, they do not resolve.
Next step
The voltage limit is the cheapest design review to run and the one most often skipped. Send
the resistor lines that sit across a rail, a bleeder or a feedback divider, and Venatech
Limited, an authorised Walsin distributor in Hong Kong, will return the crossover resistance
per case size, whether each line is voltage-limited or power-limited, and the high voltage
options with a written voltage rating from Walsin.
Send your BOM to Venatech · Browse the
Walsin chip resistor range · Read
Chip resistor power rating by case size and
Anti-surge chip resistors.