Passives for an LED Driver: High-Voltage MLCC, Anti-Surge Resistors and MOVs

0805 is the smallest Walsin Technology MLCC case size that reaches 1000 Vdc, and 1206 is the smallest that reaches 2500 Vdc. Only 111 of 927 high-voltage 0805 parts clear 1000 Vdc, and only 19 of 1,285 high-voltage 1206 parts clear 2500 Vdc — everything above that needs 1808 or larger. This how-to works through MLCC, anti-surge chip resistors and MOVs for an LED driver’s rectified AC bus using real part numbers.

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Venatech Limited, an authorised Walsin distributor in Hong Kong, holds Walsin Technology (Walsin) full MLCC and chip resistor parametric exports, 26 MLCC datasheets and two chip resistor datasheets. This post covers the three passive families an LED driver’s offline front end needs: high-voltage MLCC on the rectified bus, anti-surge chip resistors for inrush and sense paths, and MOVs on the AC input. Every part number is real and every count is of part numbers, not pieces.

Which MLCC case size gets you to 1000 Vdc or more?

Walsin’s two dedicated high-voltage MLCC series — Middle to High Voltage (4,095 parts) and Big Sizes 1825/2220/2225 (501 parts), 4,596 combined — have a hard ceiling per case size, not a smooth scale:

Case size	Voltage ceiling in this group	Parts at the ceiling	Total parts at this size
0402	250 Vdc	19	44
0603	250 Vdc	183	317
0805	1000 Vdc	111	927
1210	2000 Vdc	63	614
1206	2500 Vdc	19	1,285
1808 / 1812 / 1825 / 2220 / 2225	4000 Vdc	10–15 per size	337–570 per size

0402 and 0603 never clear 250 Vdc in this catalogue regardless of dielectric or capacitance — for anything above that on a small footprint you are outside Walsin’s dedicated high-voltage MLCC lines entirely. For the full case-size and voltage layout across all 24,025 MLCC, see Middle and High Voltage MLCC, 200V to 4kV.

How much voltage headroom does each case size actually give?

Real part numbers at the two most useful ceilings for an LED driver bus — 1000 Vdc in 0805 and 2500 Vdc in 1206 — show the same case can carry very different thicknesses at the same voltage:

Part number	Case	Dielectric	Capacitance	Voltage	L × W × T (mm)	Match / mismatch
0805B101K102	0805	X7R	100 pF	1000 Vdc	2.00×1.25×1.25	Baseline
0805B122K102	0805	X7R	1200 pF	1000 Vdc	2.00×1.25×0.80	Mismatch on thickness — thinner body, same voltage
1206B102K252	1206	X7R	1000 pF	2500 Vdc	3.20×1.60×1.25	Baseline
1206B222K252	1206	X7R	2200 pF	2500 Vdc	3.20×1.60×1.60	Mismatch on thickness — thicker body for more capacitance

For parts above 2500 Vdc, the smallest available case jumps straight to 1808:

Part number	Case	Dielectric	Capacitance	Voltage	L × W × T (mm)
1812B102K402	1812	X7R	1000 pF	4000 Vdc	4.50(+0.50/−0.30)×3.20×2.00
1812B182J402	1812	X7R	1800 pF	4000 Vdc	4.50(+0.50/−0.30)×3.20×2.50

Source for the dielectric, capacitance and voltage ranges: WTC_MLCC_Middle_and_High_Voltage.pdf and WTC_MLCC_1825_2220_2225.pdf.

What protects an LED driver’s AC input from surge?

Walsin’s varistor line gives two common LED driver input bands — 150 Vac for a 120 Vac mains design and 275 Vac for a 230 Vac mains design — scaling peak current with body size:

Part number	Series	Size	Max working voltage	Varistor voltage	Peak current	Match / mismatch
SR241K05D	Standard (D)	5 mm	150 Vac	240 Vdc	400 A	Smallest footprint, 120 Vac mains
SR241K07D	Standard (D)	7 mm	150 Vac	240 Vdc	1200 A	Higher surge margin, same line
SR431K05D	Standard (D)	5 mm	275 Vac	430 Vdc	400 A	Smallest footprint, 230 Vac mains
SR431K07D	Standard (D)	7 mm	275 Vac	430 Vdc	1200 A	Mismatch on line voltage — not interchangeable with the 150 Vac parts above

Varistor voltage is the DC clamping reference point, not the AC working rating — size against Max Working Volt. for your actual mains, with margin above the steady-state RMS value. For the full MOV selection method, see How to choose an MOV varistor.

Which chip resistors handle inrush and surge on the DC bus?

Walsin’s non-automotive Thick Film Anti-Surge Chip Resistor series — 8,340 parts — scales rated power with case size from 0805 to 2512, with a separate automotive line at 8,840 parts across two series:

Part number	Case	Resistance	Tolerance	TCR	Rated power	Match / mismatch
WK08SR270MTL	0805(2012)	0.27 Ω	±20%	≦±200	1/4 W	Baseline
WK10SR270MTL	1210(3225)	0.27 Ω	±20%	≦±200	1/2 W	Match — same resistance, double the power
WK25SR270MTL	2512(6432)	0.27 Ω	±20%	≦±200	1W	Mismatch on power only — same electrical value, largest footprint

All three share the same resistance, tolerance and TCR; only the case size and the power rating they can dissipate change. For the technology trade-off and where anti-surge differs from general purpose, see Anti-surge chip resistors. The chip resistor range is on the chip resistor product page, and MLCC on the MLCC product page.

Does Walsin certify any of these parts to a safety standard?

Not as published in the data we hold for this application. The high-voltage MLCC, anti-surge resistor and MOV parts in this post are not drawn from Walsin’s AEC-Q200 or UL-safety-certified lines — those are separate series with their own datasheets, covered in AEC-Q200 MLCC: MT vs MG series. If your LED driver design needs a safety-agency-rated capacitor across the isolation barrier rather than a high-voltage bus capacitor, that is a different part family (X1/Y2 safety-certified MLCC), not the Middle to High Voltage series used here. Venatech makes no certification or qualification claim of its own for any part — request the relevant certificate or qualification report directly from Walsin for the exact part number you intend to buy.

The short version

An LED driver’s rectified bus can stay in 0805 up to 1000 Vdc and 1206 up to 2500 Vdc; anything higher needs 1808 or larger, with no smooth scaling in between. Thickness, not just case size, moves with capacitance at a fixed voltage, so check T before you commit to a footprint. MOVs size against Max Working Volt., and anti-surge chip resistors trade case size for power rating at a fixed resistance. None of the parts in this post carry AEC-Q200 or safety-agency certification — that is a separate series.

Send us your LED driver BOM and we will tell you, line by line, which Walsin high-voltage MLCC, anti-surge resistor and MOV parts actually fit your voltage class and footprint. Or give us one incumbent part number and ask us to cross it.

Check it against the catalogue yourself. Cross-reference accepts one part number or a whole BOM column and prints the mismatches as plainly as the matches — qualification stays with you, which is the honest division of labour. Ready stock covers the chip resistor lines held in Hong Kong.

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Frequently asked questions

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