This article opens a series on high-frequency power electronics. It starts with the mechanism, because the mechanism decides the part. A snubber is a different kind of circuit from a filter, and the capacitor that fills the position is chosen for different parameters.

The Spike Is Built by Inductance, Not by the Switch

The device gets blamed for the overshoot. It only sets the speed. What converts that speed into a damaging voltage is the parasitic inductance in the commutation loop: the switch package and its internal bond wires, the busbar or trace that carries current out and back, and the capacitor’s own equivalent series inductance. Every millimetre of loop area adds inductance, and every nanohenry multiplies against the current slope.

A silicon IGBT turns off comparatively slowly. A silicon carbide MOSFET in the same socket can switch several times faster. The loop inductance has not changed. The voltage across it has, roughly in proportion.

Two things make this harder to live with than it was five years ago. The voltage margin has thinned: a 1200 V device on an 800 V bus has less headroom than a 600 V device on a 400 V bus, and the wide-bandgap device is the one being asked to run at the higher bus voltage. At the same time, the layouts that reduce inductance also concentrate current into less copper. The spike grows while the space available to absorb it shrinks. The DC-link side of that shift is covered in selecting film capacitors for 800 V SiC inverters; this series deals with the switching node instead.

What a Snubber Does With the Energy

A snubber gives the high-frequency current a shorter path. Instead of letting the energy in the stray inductance ring against the switch’s output capacitance, it puts a capacitor close to the device so the fast current has somewhere local to go. What happens to that energy afterwards is what separates the three arrangements most designers build.

The choice is not about which one is better. A C snubber is cheap and adds no loss of its own, but it moves the ring to a lower frequency rather than removing it. An RC snubber actually damps the ring, and pays for it with heat that scales with switching frequency. An RCD clamp handles more energy than either, at the cost of a diode and a slower recovery of the capacitor voltage.

Why an Ordinary Capacitor Fails Here

A snubber capacitor is asked to deliver a large current in nanoseconds. At that timescale, equivalent series inductance matters more than capacitance. A part with the right microfarads and the wrong ESL will let the spike through, because the inductance blocks the very current the snubber was added to carry. This is the most common reason a snubber measures as though it were not there.

Film capacitors hold this position for a structural reason. A metallized film part in a flat case brings the electrodes out to terminals that are physically close to each other, which keeps loop area small and ESL low. The metallization also self-heals: a local breakdown vaporizes the electrode around the fault instead of shorting the part, provided the energy available is below what the film can clear.

The format also survives the dv/dt. A snubber capacitor sees the same fast voltage edge that stresses the switch, and polypropylene film handles repeated high dv/dt without the capacitance drift that Class II ceramics show under voltage and temperature. Where the pulse energy is modest and the capacitance small, a ceramic part with a suitable dielectric can work, but the film part is the default for snubber duty above a few hundred volts and above a few nanofarads, which is where ceramics stop being practical.

Matching the Snubber Capacitor to Its Position

Where the snubber sits decides what it has to survive. A capacitor across a bridge leg sees a fast edge on every switching cycle and has to hold its value over millions of them. A snubber across a rectifier sees the reverse recovery of the diode instead. The energy per event and the repetition rate are different, and they drive different parts of the specification.

What Goes Wrong on the Bench

Snubber problems tend to appear in the same four places, and none of them are visible on the capacitor’s datasheet.

The most common is a capacitor mounted a centimetre or two from the device. At that distance the part has already given back the inductance it was chosen to avoid, because the leads to it and back are part of the loop. A snubber only works when it sits at the terminals, with the return path as short as the outgoing one.

Then there is the dv/dt rating nobody checked. The snubber capacitor sees the fast edge directly, and a film part chosen for capacitance and voltage but not for dv/dt will lose capacitance as the metallization degrades. That failure is quiet. The spike creeps up over months instead of appearing as a hard fault, which is why it usually turns up on a returned unit rather than in the lab.

Resistor values get copied from older schematics more often than they get calculated. In an RC snubber the resistor sets both the damping and the loss. Too low and the snubber pulls a large current spike out of the switch on every cycle. Too high and the ring is barely touched. If the switching frequency has changed since that schematic was drawn, the old value no longer applies to it.

Last is heat with nowhere to go. Loss in an RC snubber scales with switching frequency, which is exactly the parameter that went up when the design moved to wide-bandgap devices. A snubber that ran cool on an IGBT design can end up the hottest part on the board after the switch to silicon carbide.

Where This Series Goes

Everything above is about whether a snubber works. None of it answers the other question, which is what value goes in the position. The mechanism says a snubber is needed; the numbers decide whether it does anything. That is where the next article in the series picks up: reading a dv/dt rating against an actual edge, sizing capacitance from the energy the loop must absorb, and calculating the RC resistor rather than copying one.

Common Questions About Snubber Capacitors

Can I use a ceramic capacitor instead of film in a snubber?

For small, low-energy snubbers at modest voltages, yes, and a Class I ceramic is often the better part because its capacitance does not move with voltage or temperature. The limit is practical: above a few nanofarads of capacitance and a few hundred volts, ceramic parts become large, expensive or simply unavailable, and film takes over.

Why does my snubber resistor run hot?

Because it is doing its job. An RC snubber removes energy from the loop on every transition, and the resistor is where that energy becomes heat. The dissipation scales with both the capacitance and the switching frequency, so a design that increased its switching frequency needs the loss recalculated even if nothing else changed.

What size capacitor do I need for a snubber?

Size it from the energy the loop has to absorb, not from the capacitance values you see in other designs. The stored energy in the stray inductance depends on the current at turn-off and the loop inductance. The snubber capacitance is then chosen so the resulting voltage rise stays inside the margin the device has left. Calculation first, then verification on the bench with the actual layout.

Does a snubber replace good layout?

No, and treating it that way is how designs end up with a snubber that cannot do its job. Reducing loop area is still the primary move, and it is free. The snubber cleans up what is left after the layout has been made as tight as the mechanical design allows.

Xuansn manufactures metallized film capacitors for snubber and high-frequency power duty, including the CBB81 series used across bridge legs and rectifier positions. If you send the switching frequency, the current at turn-off and the loop inductance you expect, we will come back with a capacitance value, a dv/dt rating and a part number. Reach us at coco@xuanxcapacitors.com.

The post Snubber Capacitors: Where the Voltage Spike Comes From and What Stops It appeared first on Xuansn Capacitor.

Most DC-link selection guides start with the bus voltage. For a solar inverter, the duty cycle comes first, because it sets the thermal budget the DC-link film capacitor has to live inside.

The Duty Cycle Comes First

A solar inverter starts with the sun and stops at dusk. Across one day its DC-link capacitor sees the bus voltage rise, hold through the middle hours, then fall away. Case temperature climbs, plateaus, then drops back overnight. On its own, none of that is severe. It becomes severe when it repeats every day.

Roughly nine thousand thermal cycles

Twenty-five years of daily cycling works out to about nine thousand thermal cycles, each one expanding and contracting the film, the metallization and every solder joint in the assembly. A capacitor specified only against its rated temperature will pass the first thousand without complaint. What it does at the end of the ninth thousand is the question a datasheet does not answer directly.

That reframes the exercise. Rather than asking whether the part survives its maximum ratings, ask how much of its life the daily cycle consumes, and whether the answer still leaves margin after the hottest week of the year.

What the DC Bus Voltage Sets

Bus voltage is the first hard constraint, and in solar it comes from the system architecture rather than from the inverter designer.

The capacitor is rated above the bus voltage, with headroom for switching overshoot and for the grid-side transients that reach back through the bridge. How much headroom is a design decision, and it trades directly against size and cost: a higher-rated film of the same capacitance is physically larger and more expensive.

Insulation coordination matters as much as the rating. In a 1500 V system the clearance and creepage distances inside the capacitor, and the way its terminals are potted, decide whether the part holds up under damp heat and pollution. A capacitor that meets its voltage rating on a bench test can still track across a contaminated surface in a field installation.

Ripple Current, Heat, and the Daily Cycle

Ripple current turns electrical stress into thermal stress, and thermal stress is what consumes life. In a solar inverter the ripple comes from two directions: the switching current of the inverter bridge, and the low-frequency component from the AC side.

The DC-link film capacitor has to absorb both. Its ESR converts that current into heat, the heat raises the hot spot above the case temperature, and the hot-spot temperature sets the rate at which the film degrades.

Why daily heat dose matters more than the peak hour

Designers often size against the peak ambient day of the year. The more useful number is the cumulative thermal dose across the whole day, because that is what the film actually accumulates. A capacitor that runs moderately hot for eight hours may age faster than one that runs very hot for one, and the baseline is set by the site’s daily average ambient rather than its record high.

Mounting matters for the same reason. A capacitor bolted to a heatsink, or to a busbar that carries heat away, runs cooler than one sitting in still air inside a sealed enclosure. The same part can have two very different service lives depending on where the inverter designer puts it.

Turning 25 Years Into a Specification

The lifetime figures in a film capacitor datasheet are quoted at a reference voltage and a reference hot-spot temperature. Moving to the real operating point is a two-part calculation: a voltage factor, and a temperature factor that follows an Arrhenius-type relationship, where every ten degrees of hot-spot reduction roughly doubles the expected life.

That rule is the most useful sizing lever in the whole design. Running a capacitor well below its rated voltage, and keeping its hot spot cool, buys life far more cheaply than specifying a larger can.

An inverter headed for a desert installation and one headed for northern Europe face the same 25-year target with very different ambient profiles. The capacitor that suits one may be over-specified or under-specified for the other, so work the numbers against the site rather than the catalogue. The same derating logic applies to higher-frequency designs, where faster switching changes what the capacitor sees.

Where Solar Installations Actually Fail

Field failures usually come from the interaction between the part and its environment rather than from a part that was under-rated on paper.

Moisture is the most common thread. A non-hermetic film capacitor absorbs water through its potting over years of damp heat, and the absorbed moisture raises dielectric loss and eventually supports corrosion of the metallization. Parts specified for high humidity and the right pollution degree survive it. Parts chosen on capacitance and voltage alone often do not.

Mechanical stress comes next. A large DC-link capacitor mounted on stiff busbars, inside a cabinet that expands and contracts daily, will see its terminals loaded in a way no datasheet test reproduces. Flexible connections and proper support belong in the capacitor specification rather than in the assembly notes.

Then there is the mismatch that shows up as a warranty claim: a bank of capacitors where one part runs measurably hotter than the rest because current sharing is uneven. The cool ones have margin to spare while the hot one consumes its life first.

Selection Checklist

Before quoting a part for a solar design, confirm the following.

Start with the DC bus voltage class, and the headroom the design allows above it, including switching overshoot. Then the worst-case continuous ripple current rather than the nominal figure. The hot-spot temperature deserves its own estimate: what the part will actually reach inside the enclosure, at the site’s daily average ambient. From those three you can work out expected life, with the voltage and temperature factors applied. Two more decide whether the part survives the field: the humidity and pollution degree the installation has to meet, and how the part is mounted, since the mounting decides whether heat leaves the part or stays with it.

If any of those is unknown at the quotation stage, say so. A capacitor quoted against a bus voltage alone is a guess, and in a 25-year application a guess is expensive to correct in the field.

FAQ

Why not use an electrolytic capacitor for the DC link in a solar inverter?

Some small inverters do. The difficulty is life. An electrolytic’s electrolyte dries out over time, and the rate depends on temperature in the same way film does, but from a much shorter starting point. In an application expected to run for 25 years in a hot enclosure, the film part is usually the one still meeting the target at the end.

Does a higher voltage rating always mean longer life?

It helps, but it is not free. A higher-rated film of the same capacitance is physically larger, which can make it harder to keep cool and harder to fit. The better question is whether the extra margin is buying life the design actually needs.

How do I know the hot-spot temperature before I have a prototype?

Estimate it from the ripple current, the ESR at the switching frequency, and the thermal resistance of the mounting. Then measure it on the first prototype at the highest expected ambient and correct the lifetime calculation. A datasheet curve on its own will not tell you where the inverter puts the part.

Xuansn supplies DC-link film capacitors for solar and energy storage inverters, and we quote against the duty cycle rather than the headline rating. Send your bus voltage, ripple current and expected hot-spot temperature to coco@xuanxcapacitors.com and we will come back with a part and a lifetime estimate.

The post DC-Link Film Capacitors for Solar Inverters: Sizing for a 25-Year Duty Cycle appeared first on Xuansn Capacitor.

That distinction stopped being academic in 2026. MLCC lead times have stretched toward ten months on AI server demand, and buyers who once designed in an MLCC without a second thought are now being asked to look at alternatives. Film capacitors are the most common answer — but only where the electrical job allows it. This guide compares the two technologies on the parameters that actually decide the choice, then shows where a swap is realistic and where it is a reliability risk.

MLCC vs Film Capacitor at a Glance

Where MLCC Wins

The MLCC’s advantage is density and speed. A multilayer ceramic part puts a useful capacitance into a package a few millimetres across, with ESR and ESL low enough to work at hundreds of megahertz. That is why it dominates decoupling and bypass: an IC’s power pin needs a capacitor that can respond to a fast transient and sit right next to the pin, and no film part competes on that combination of size and frequency response.

Class 1 ceramics such as C0G (NP0) add a second strength: a capacitance that barely moves with temperature, voltage or time. For timing circuits, oscillators and RF matching, that stability is worth more than capacitance density, and it is the reason C0G parts hold their place even where a film capacitor would be electrically acceptable.

The limits appear as soon as the job changes. Class 2 dielectrics such as X7R and X5R give far more capacitance per volume, but they lose it under DC bias — a part rated 10 µF can measure well under that at half its rated voltage — and they age and drift with temperature. Where the design needs a defined capacitance at the working voltage, the MLCC’s headline number can be misleading.

Where Film Wins

Film capacitors are built for power. A metallized polypropylene or polyester part handles high voltage, high ripple current and continuous AC stress without the capacitance collapse that afflicts Class 2 ceramics. Its capacitance is stable across voltage and temperature, so the value on the datasheet is the value in the circuit. For a DC-Link in an 800 V SiC inverter, that predictability is not a luxury; it is the basis of the ripple and lifetime calculation.

The second advantage is how it fails. Metallized film is self-healing: a local breakdown vaporizes a tiny area of the metallization and clears the fault, so the capacitor usually loses a little capacitance and keeps working rather than shorting. That behaviour is why film parts are preferred in snubber, safety and DC-Link positions, where a short-circuit failure can take out a switching device or trip a protection circuit.

The trade-off is size and cost at low voltage. A film part that matches an MLCC’s capacitance in a 5 V decoupling position would be many times larger and more expensive, which is why the substitution only makes sense where the electrical duty justifies it. If you are comparing film families, our guide to film capacitor types and how they work covers the metallized and foil constructions and what each is for.

Can Film Actually Replace MLCC?

Sometimes yes, sometimes no, and the line is drawn by the circuit’s job rather than by the capacitor’s specifications.

Positions where film is a real substitute

Bulk and DC-Link capacitance is the clearest case. Here the requirement is energy storage and ripple handling at a defined voltage, and a film part often does it better than a bank of Class 2 MLCCs, because it does not lose capacitance under bias and it tolerates far more ripple current. Snubber circuits are a second natural fit, where the self-healing failure mode and high dV/dt capability matter. AC line filtering and EMI positions — the X and Y capacitors in a power supply — are already film or safety-ceramic territory, and substituting a film part there is standard practice rather than a workaround.

Positions where it is not

Decoupling a fast digital or RF IC is not one of them. The MLCC’s low ESL and small package are what let it sit beside the pin and respond before the voltage collapses; a film part with a longer internal path and larger body cannot take that role, and trying to force it produces a design that is larger and still worse. High-density filtering at low voltage has the same problem, and so do timing and RF circuits that depend on a stable, small-value part in a small footprint. In these positions the right response to an MLCC shortage is to qualify a second MLCC source, not to redesign around a film capacitor.

How the 2026 Supply Picture Changes the Decision

Supply risk is now part of the selection. With MLCC lead times approaching ten months, a design that depends entirely on one ceramic part family carries a schedule risk that no amount of engineering elegance fixes. The practical response is a dual-design strategy: keep the MLCC where its electrical role is irreplaceable, but move the positions where a film part is genuinely equivalent onto film, so that a shortage in one family does not stop the whole board.

That is a sourcing decision as much as a technical one. The demand behind the current shortage is the same AI server power demand that has stretched the whole passive components chain, and it is unlikely to reverse quickly. Buyers who map which positions can accept a film alternative before the shortage reaches them are the ones who keep their production lines running.

A Selection Checklist

Start from the electrical job. Is this position storing energy, filtering ripple, snubbing a switch, or decoupling a fast pin? Only the first three are film candidates.

Check the voltage. Film wins comfortably above a few hundred volts; below that, the size penalty grows and the MLCC usually stays.

Compare at the working voltage, not the rated voltage. An MLCC’s Class 2 capacitance is measured at a fraction of its rating, so compare the film value against the MLCC’s derated value, not its headline number.

Check the failure mode. Where a short is dangerous, film’s self-healing behaviour is a safety argument as well as a technical one.

Check the footprint and the board. A film part that does not fit is not a substitute. Measure before you commit.

Qualify before you need it. The value of a film alternative comes from having it qualified when the MLCC goes short, not from discovering it during a shortage.

FAQ

Is a film capacitor a drop-in replacement for an MLCC?

No. The capacitance may match, but the ESR, ESL, size and self-healing behaviour are different, so a film part is a substitute only where the circuit’s requirements allow it — typically bulk, DC-Link, snubber and AC filtering, not decoupling.

Why does an MLCC lose capacitance under DC bias but a film capacitor does not?

The ferroelectric ceramic in Class 2 dielectrics such as X7R changes its dielectric constant as the applied field rises, so the measured capacitance falls with voltage. Film dielectrics are not ferroelectric in the same way, so their capacitance stays essentially flat across the working voltage.

Are film capacitors more expensive than MLCCs?

At low voltage and small capacitance, yes — often several times more per µF. At high voltage and high ripple current the comparison reverses, because a film part can replace a large bank of ceramics and tolerates the ripple the ceramics cannot.

Which is better for high-temperature operation?

It depends on the dielectric and the construction rather than the technology label. Class 1 ceramics hold capacitance across a wide temperature range, while Class 2 parts drift. Film parts are stable with temperature but have their own upper limit, typically 85 °C to 125 °C depending on the film and construction. Always check the specific datasheet.

Choosing between the two is easier when you compare them on the parameter that decides the position, not on a single headline number. If you are weighing a film alternative against an MLCC that has gone short or expensive, send us the circuit conditions, the working voltage and the capacitance you need, and we will confirm whether a film capacitor is a genuine substitute or whether the multilayer ceramic capacitor should stay in the design. We will quote against the real specification and lead time you need.

The post MLCC vs Film Capacitor: Which One to Choose in 2026 appeared first on Xuansn Capacitor.

Why 800V SiC Inverters Demand Specific Film Capacitor Specs

Silicon-carbide switches turn on and off in nanoseconds, generating dv/dt slopes measured in tens of kilovolts per microsecond. Any stray inductance in the DC bus converts that di/dt into a voltage spike—L · di/dt—which adds directly to the 800V rail. Electrolytic capacitors, with ESL often exceeding 50 nH, amplify those spikes beyond the semiconductor’s safe operating area. Film capacitors offer ESL as low as 10–20 nH in well-designed packages, keeping transient over-voltage manageable.

The 800V bus itself sits near the upper edge of many legacy capacitor families. Film dielectrics—polypropylene in particular—scale cleanly to 1000V, 1200V, and beyond, with voltage derating rules that preserve decades of service life. High switching frequencies, common in SiC designs (50–200 kHz), spread ripple current across a wide spectrum; film’s low dissipation factor keeps self-heating in check where electrolytics would overheat.

Step 1: Voltage Rating and Derating

Start with the DC-bus nominal voltage—800V in this case—and multiply by 1.3 to 1.5. That yields a required capacitor rating of 1040–1200V DC. The extra margin accounts for manufacturing tolerance, transient over-voltage during regenerative braking or fault conditions, and temperature-dependent dielectric strength. Running a 1000V-rated capacitor at 800V leaves 20 % headroom; a 1200V part offers 50 %, which extends life in harsh environments.

Industry practice leans toward 30–40 % derating for mission-critical applications (automotive traction, grid-tie inverters) and 20–30 % for cost-sensitive industrial drives. If peak transients can reach 900V for milliseconds, a 1200V rating becomes the safer choice. Consult the manufacturer’s voltage-life curves: a part run at 70 % of rated voltage may last ten times longer than one stressed at 90 %.

Step 2: ESL and ESR for High dv/dt

Equivalent series inductance determines how much voltage spike appears during a fast switching edge. The formula V_spike = L · di/dt shows that even 30 nH of ESL, combined with a 1000 A/µs current slew rate, produces a 30V transient. SiC MOSFETs routinely hit 2000–5000 A/µs in hard-switched topologies, so ESL must stay below 20–50 nH. Film capacitors achieve this through stacked-foil construction, short internal leads, and surface-mount or low-profile packages.

Equivalent series resistance governs ripple-current heating. A 20 mΩ ESR dissipating 10 A_rms ripple generates 2 W of heat—manageable with good thermal coupling to a heat sink or copper plane. Film ESR remains nearly flat across frequency, unlike electrolytics where ESR rises at high frequency. Parallel connections reduce both ESL and ESR: two identical capacitors in parallel halve the net inductance and quarter the resistance.

Step 3: Ripple Current Rating

Ripple current in an 800V SiC inverter has two origins: switching ripple from the DC-DC converter or active front end, and load-dependent harmonics from the three-phase inverter bridge. The total RMS ripple current is the root-sum-square of all frequency components.

DC-link capacitance sets the voltage ripple: C = I · Δt / ΔV, where I is the peak ripple current magnitude, Δt is half the switching period, and ΔV is the acceptable voltage deviation. For an 800V bus with ±1 % ripple tolerance (ΔV = 8V) and 100 kHz switching (Δt = 5 µs), a 20A peak current demands C = (20 A × 5 µs) / 8V ≈ 12.5 µF. Real designs add margin and account for capacitor aging, so 20–30 µF is common. High-power traction inverters (100+ kW) may use 100–200 µF or more.

Manufacturers specify ripple-current rating at a reference frequency (often 10 kHz or 100 kHz) and ambient temperature. Datasheet curves show how the rating changes with frequency and temperature. Film capacitors usually maintain or slightly improve their rating as frequency rises. Always verify that your calculated ripple current, adjusted for all harmonics, stays below the derated limit.

Step 4: Temperature Rating and Lifetime

Automotive traction inverters operate from −40 °C to +125 °C; industrial VFDs span −25 °C to +105 °C. Film capacitors are available in matching temperature classes: 85 °C, 105 °C, and 125 °C. The temperature rating refers to the maximum case or core temperature, not ambient. Self-heating from ripple current adds 5–20 °C depending on package size and thermal coupling.

Lifetime follows an Arrhenius relationship: every 10 °C reduction in core temperature roughly doubles service life. A capacitor stressed at 90 % of rated voltage and temperature might last 10 000 hours; derate to 70 % and life extends to 100 000 hours or more. Film dielectrics do not dry out like electrolytic electrolyte, so end-of-life is typically defined by gradual capacitance loss (5–10 %) or an increase in ESR.

Xuansn offers 800V to 1200V-rated polypropylene film capacitors in compact SMD and radial-lead formats, designed for low ESL and high ripple-current capability in SiC inverter DC-link stages. Typical ESL is under 30 nH, and 125 °C temperature class ensures automotive-grade reliability.

Common Questions About Selecting Film Capacitors for SiC Inverters

What DC-link capacitance value should I use?

Calculate C = I · Δt / ΔV using the peak ripple current, half the switching period, and your acceptable voltage ripple. For an 800V bus with ±1 % ripple and 100 kHz switching, expect 10–30 µF per kilowatt of inverter power. High-power systems may need 100–200 µF total, often split across multiple capacitors in parallel.

Can I substitute electrolytic capacitors for film capacitors?

Electrolytic capacitors offer higher capacitance density and lower cost, but their ESL (50–200 nH) and ESR cannot match film performance. At 800V and SiC switching speeds, the resulting voltage spikes and self-heating typically force you back to film. Electrolytic bulk capacitance is sometimes placed in parallel with film snubbers—the electrolytic handles low-frequency energy storage, the film suppresses high-frequency transients.

How do I verify my selection is adequate?

Prototype testing is essential. Measure DC-bus voltage ripple with a high-bandwidth oscilloscope and current probe on the capacitor terminals. Confirm that peak-to-peak ripple stays within ΔV, that no over-voltage spikes exceed the semiconductor rating, and that capacitor case temperature remains 10–20 °C below the rated maximum.

Choosing film capacitors for an 800V SiC inverter requires matching voltage rating (1.3–1.5× derating), ESL (under 20–50 nH), ripple current (calculated from switching and load harmonics), and temperature class (125 °C automotive, 105 °C industrial) to your application’s electrical and thermal environment. Our earlier article on 800V SiC DC-link requirements explains why these parameters matter; this guide shows you how to select them in practice. Xuansn manufactures high-voltage polypropylene film capacitors optimized for SiC inverter DC-link, snubber, and filter stages—low ESL, high ripple current, and automotive-grade temperature ratings. Contact our team at coco@xuanxcapacitors.com with your bus voltage, switching frequency, ripple current, and temperature range, and we will recommend a part number with verified performance data. Quote turnaround in 24 hours.

The post How to Select Film Capacitors for 800V SiC Inverters appeared first on Xuansn Capacitor.

This is the first article in our 800 V SiC series, following our work on eVTOL DC-link film capacitors. The question is specific: when the inverter goes SiC at 800 V, what changes for the DC-link capacitor – and what should you specify for it.

What Actually Changes When the Inverter Goes SiC

Silicon carbide switches do two things differently than silicon IGBTs. They switch faster, so the switching frequency moves from the single-digit kilohertz range up to tens of kilohertz. And they produce steeper voltage edges, because the transition from on to off happens in a fraction of the time.

Both changes land on the DC-link capacitor. A higher switching frequency shifts the ripple current the capacitor sees to higher frequencies and adds more harmonics. A steeper dv/dt means the capacitor has to absorb and release charge faster at the bus. The result is the same: more ripple current to carry, more self-heating, and a tighter temperature budget.

This is why the 800 V platform is not just a higher-voltage version of a 400 V design – the capacitor spec moves on two axes at once.

The Three Numbers an 800 V SiC Inverter Demands

When you specify a DC-link film capacitor for an 800 V SiC inverter, three numbers carry most of the decision.

Ripple current at the switching frequency

Ripple current is the alternating current the capacitor handles on top of the DC bus. With SiC running at tens of kilohertz, the ripple sits higher in frequency and carries more harmonics, so the RMS current the capacitor sees goes up for the same power level. The rating that matters is the ripple current capability at your actual switching frequency – not at a reference frequency from the datasheet.

ESR and the heat it makes

Equivalent series resistance converts part of that ripple current into heat inside the capacitor. A lower ESR means less self-heating for the same ripple – and in a compact 800 V inverter, space for cooling is limited, so ESR quickly becomes the number that decides whether the capacitor survives. Film capacitors hold a low, stable ESR across temperature, which is one reason they suit this position well.

Voltage rating and dv/dt tolerance

The bus runs near 800 V, so the capacitor must be rated well above that with margin for overshoot during switching transients. And with SiC’s steep edges, the capacitor also needs enough dv/dt tolerance to absorb those transitions without generating excessive internal stress. Voltage rating and transient capability go together.

The pattern is clear: each move from IGBT to SiC tightens the capacitor’s requirement on ripple, ESR and voltage capability at once.

Why Film Beats Electrolytic in This Position

At the DC-link position of an 800 V SiC inverter, film has a structural advantage. A film capacitor carries a low, temperature-stable ESR and handles high ripple current, while its self-healing property means a localised failure clears itself rather than shorting the bus. An electrolytic capacitor in the same position drifts in ESR as it ages and heats – acceptable on a bulk rail, but harder to justify where the ripple current is high and the edge is steep.

This is the same argument our take on why eVTOL power electronics need DC-link film capacitors makes for electric aviation; here it applies to SiC drives.

Specifying for the 800 V Platform

When you are choosing a part, work down the list in order: ripple current capability at the switching frequency first, then ESR against your heat budget, then voltage rating with derating for overshoot, and finally the dv/dt tolerance and the form factor that fits the inverter. Checking them in that order catches the most common 800 V failures before the design is locked.

Xuansn manufactures film capacitors built for high-ripple, high-voltage power stages like this. Our film capacitor range covers the ratings an 800 V SiC DC link needs, and the film capacitor guide walks through the full selection logic.

Common Questions

What switching frequency does an 800 V SiC inverter typically run?

SiC inverters commonly switch in the tens of kilohertz – substantially higher than the few kilohertz typical of IGBT designs. Check the datasheet for your exact number, because the ripple current rating that matters is the one at your real switching frequency.

Do I need a film capacitor or can an electrolytic work at 800 V?

At the DC-link position with high ripple and steep edges, film is usually the better choice for its low ESR and self-healing. An electrolytic can suit a bulk rail where ripple is lower, but the DC link of an 800 V SiC inverter leans film.

What voltage rating should an 800 V DC-link capacitor have?

Rate well above the bus with margin for overshoot during switching. The exact figure depends on your overshoot envelope – confirm against the real transient, not just the nominal bus voltage.

The post How 800V SiC Inverters Change DC-Link Film Capacitor Requirements appeared first on Xuansn Capacitor.

In our look at eVTOL DC-link film capacitors, we covered why film is the right choice for electric aviation and high-power drives. This article walks through how to pick the part.

Start with Voltage Rating and Derating

DC-link capacitors sit on a bus that can swing above nominal during load steps and regeneration. A common rule is to rate the capacitor at 1.5-2x the nominal bus voltage to leave margin for overshoot. For an 800 V bus, that points to parts rated at 1,000 V or higher.

• Check the rated DC voltage and the surge or transient capability.
• Leave derating margin for switching overshoot and operating temperature.

Then Ripple Current and ESR

The DC-link capacitor must survive the ripple current at your switching frequency. Higher ripple heats the part from inside; low ESR keeps that heat down.

• Ripple current rating – the part must handle the RMS ripple it will actually see.
• ESR at the switching frequency – lower ESR means less self-heating and less ripple voltage on the bus.
• Temperature rise – derate the ripple rating to your real ambient.

Energy, Capacitance and Size

For eVTOL and high-power drives, the DC-link also stores energy that helps ride through brief load steps. Capacitance and voltage set the stored energy (1/2 x C x V2), and that drives the physical size:

• Capacitance – pick for the ripple current and hold-up the drive needs.
• Voltage – higher rating increases size; match to the bus with derating.
• Form factor – box, cylindrical or module; weight matters on an aircraft.

Our DC-link film capacitor application guide covers the sizing logic in detail, and the film capacitor guide explains the types.

Selection Quick Reference

In practice, the datasheet is the contract: check the ripple current rating at your switching frequency, not just at the reference frequency. If the part is borderline on temperature rise, moving to a larger package or a lower ESR series often solves it before you build. For eVTOL especially, the weight and volume budget makes this a real design trade-off, not an afterthought.

A good selection process ends with a cross-check against the inverter operating envelope – the worst-case voltage, the ripple at full load, and the ambient temperature in the enclosure.

Common Selection Mistakes

Two mistakes come up most often. The first is picking capacitance first and voltage second – the reverse order leaves the part vulnerable to overshoot. The second is ignoring ripple current at the actual switching frequency, which causes premature heating even when the capacitance looks right. Start with voltage and ripple, then size for energy.

Xuansn publishes ripple and lifetime data for every DC-link film series, so the numbers in the datasheet match the part you receive.

Common Questions About Choosing DC-Link Film Capacitors

What voltage rating do I need for an 800 V bus?

Typically 1,000 V or higher, to give derating margin against overshoot during switching and regeneration.

How do I size the capacitance?

Size for the ripple current and the hold-up energy the drive needs; higher capacitance and voltage store more energy but increase size.

Why does ESR matter for DC-link film capacitors?

ESR converts ripple current into heat. Lower ESR at the switching frequency keeps the capacitor cool and extends its life.

What to Read Next

For the wider AI power picture, see why AI server power demand is exploding and our server capacitors for AI power.

Need DC-link film capacitors for eVTOL or high-power drives? Xuansn Capacitor manufactures film capacitors for DC-link duty – our engineers will reply within 24 hours with feasibility and a quote.

✉ coco@xuanxcapacitors.com | ☎ +86-769-8166 8821 | Send your specification

Sources: Industry practice for DC-link capacitor selection (voltage derating, ripple, ESR); eVTOL powertrain requirements.

The post How to Choose a DC-Link Film Capacitor for eVTOL and High-Power Drives appeared first on Xuansn Capacitor.

The post eVTOL Power Electronics Need DC-Link Film Capacitors appeared first on Xuansn Capacitor.

The post CBB22 Capacitor Value: Read the Code and Choose the Right Part appeared first on Xuansn Capacitor.

The post CBB Capacitor: Types, Working Principle, Applications & Selection Guide appeared first on Xuansn Capacitor.

Film capacitors are among the most widely used passive components in power electronics, motor drives and EMC work. They are non-polarized, self-healing and highly reliable, which is why engineers reach for them when an electrolytic capacitor will not do. This guide covers how they are built, the main types, the parameters that matter, where they are used, and how to pick one.

What Is a Film Capacitor?

A film capacitor uses a thin plastic film as its dielectric. Two layers of film are wound or stacked with electrodes between them to form a compact component that stores electrical energy.

Unlike electrolytic capacitors, film capacitors are non-polarized, meaning they can be connected to a circuit in either direction. This makes them suitable for AC circuits where the current direction changes constantly.

The plastic film dielectric is the defining feature. It gives film capacitors several advantages over other technologies:

• Self-healing – when a small dielectric breakdown occurs, the metal electrode vaporizes around the fault, restoring insulation
• Low ESR and low inductance – ideal for high-frequency and high-ripple applications
• Long service life – no liquid electrolyte to dry out
• High voltage and current handling – available up to thousands of volts
• Stable capacitance over temperature and time

These properties make film capacitors the first choice for power electronics, motor control, EMI suppression, and high-reliability industrial applications.

How Does a Film Capacitor Work?

A film capacitor stores energy in an electric field between two conductive electrodes separated by the plastic film dielectric. When voltage is applied, charges accumulate on the electrodes.

Constructively, two metal electrodes (typically vacuum-deposited aluminum or zinc) sit on either side of a plastic film, wound into a cylinder or stacked into a flat block, then sealed with resin. Because there is no liquid electrolyte, film capacitors do not dry out and their capacitance stays stable over decades of operation – a key reliability advantage over aluminum electrolytic capacitors.

Types of Film Capacitors

Film capacitors are classified primarily by the dielectric material. Each material has different electrical characteristics and applications.

1. Polypropylene Film Capacitors (PP)

The most widely used film dielectric for power applications. Very low dielectric loss, high insulation resistance, excellent high-frequency behavior and good self-healing. Typical ratings up to 400V, 630V, 1000V and higher. Common series: CBB21, CBB22, CBB60, CBB61, CBB81. Applications: motor run, power factor correction, DC-link, snubber, high-frequency circuits.

2. Polyester Film Capacitors (PET / Mylar)

The most economical film type, widely used in general-purpose and consumer electronics. Low cost and compact, but higher dielectric loss and poorer high-frequency performance than polypropylene. Applications: coupling, bypass, timing circuits.

3. Polyphenylene Sulfide (PPS)

High-temperature stability (up to ~150°C), stable capacitance over temperature. Used in automotive, timing, and precision applications.

4. Polystyrene (PS)

Very low dielectric absorption and loss, but limited to low-temperature/low-voltage use. Rare in modern products.

5. PTFE (Teflon)

Extremely low loss, very high temperature rating. Expensive, used in aerospace and high-reliability military applications.

By Construction

Type	Structure	Characteristics
Metallized film	Thin metal layer deposited directly on film	Self-healing, smaller size, most common
Film / foil	Separate metal foil layers with film	Higher current handling, no self-healing, used for high-current pulse applications

By Safety Classification

X capacitors connect across the line (line-to-line). X1, X2, X3 classes by impulse withstand. Y capacitors connect from line to ground. Y1, Y2, Y4 classes by isolation rating. Safety film capacitors are certified to EN 60384-14, UL 60384-14 and IEC 60384-14, and are mandatory in AC mains-powered equipment for EMI suppression.

Key Parameters & How to Read Them

• Rated Voltage (UR) – the maximum continuous DC voltage. Always derate: operate at 70-80% of rated voltage for long life.
• Capacitance (C) – measured in µF, nF, or pF, with tolerance typically ±5% (J), ±10% (K), or ±20% (M).
• Dissipation Factor (DF / tan δ) – a measure of dielectric loss. Lower is better. Polypropylene has very low DF, polyester is higher.
• dv/dt – the maximum rate of voltage change in V/µs. Critical for snubber and high-pulse applications.
• ESR – combined resistance of the capacitor. Lower means less energy lost as heat.
• Insulation Resistance (IR) – how well the dielectric resists leakage current. Higher is better.
• Operating Temperature Range – typically -40°C to +85°C (or +105°C for high-temperature grades).
• Self-Healing – the ability to recover from localized dielectric breakdown.

Film Capacitor Applications

DC-Link in Inverters and Converters

DC-link film capacitors smooth the DC bus voltage in frequency converters, EV inverters, solar inverters and wind converters. Low ESR and high ripple current capability make film the preferred choice over electrolytic in high-power systems. Related products: Film capacitor range.

Motor Run and Start Capacitors

Motor run capacitors provide phase shift in single-phase AC motors (fans, pumps, compressors, air conditioners). Motor start capacitors provide a high-torque starting pulse. Related products: CBB61 motor capacitor.

EMI Suppression (X2 / Y Capacitors)

Safety film capacitors suppress electromagnetic interference in AC mains-powered equipment – power supplies, appliances, industrial machines. They are required for EMC compliance. Related products: X2 / X safety capacitors and Y capacitors.

Snubber Circuits

In IGBT/SCR power switches, snubber film capacitors limit dv/dt and suppress voltage spikes during switching transitions, protecting the semiconductor. Related products: Snubber capacitors.

High-Frequency / Resonant Circuits

Polypropylene film capacitors handle high-frequency AC currents in induction heating, resonant converters and RF filtering with low loss.

Power Factor Correction & Pulsed Power

In industrial power systems, film capacitors compensate reactive power and improve power factor. High-voltage film/foil capacitors also deliver controlled high-energy pulses in medical equipment, lasers and research.

Film vs Electrolytic vs Ceramic: Which to Choose?

Criterion	Film Capacitor	Electrolytic	Ceramic (MLCC)
Polarity	Non-polarized	Polarized	Non-polarized
Capacitance density	Medium	Very high	Low-medium
Voltage rating	High	Medium-high	Medium
ESR / loss	Very low	High	Medium
High-frequency	Excellent	Poor	Good
Lifespan	Very long	Limited (dries out)	Long
Self-healing	Yes (metallized)	No	No

Rule of thumb: need high capacitance in small space, DC only → electrolytic. Need high-frequency/low-loss/high-voltage/long-life → film. Need small-value decoupling → ceramic.

Film Capacitor Selection Guide (Step by Step)

1. Define the circuit function – DC-link, motor run, EMI suppression, snubber, coupling, or resonant?
2. Determine rated voltage – operating voltage × 1.25-1.5 derating factor. For AC, use the AC voltage rating.
3. Calculate capacitance – based on ripple current, energy storage, or impedance requirement.
4. Check dv/dt – for switching circuits, verify the dv/dt rating exceeds the actual switching speed.
5. Verify ripple current / ESR – ensure the capacitor can handle the RMS ripple without overheating.
6. Select the dielectric – polypropylene for power/high-frequency, polyester for general purpose.
7. Check safety certification – for AC mains use, select X2/Y capacitors with EN/IEC/UL certification.
8. Confirm temperature range – cover ambient temperature with margin.
9. Choose packaging – radial lead, axial, SMD, or screw terminal based on mounting.

Film Capacitor Lifetime and Reliability

Film capacitors are among the most reliable capacitor technologies. Key factors affecting lifetime: voltage stress (derating extends life), temperature (every 10°C rise roughly halves lifetime), ripple current (excessive ripple heats internally), and moisture (keep in dry storage). Under normal operating conditions, quality film capacitors can last 20+ years.

Common Film Capacitor Failure Modes

• Open circuit – often caused by electrode corrosion or mechanical stress
• Capacitance loss – gradual degradation of the dielectric
• Short circuit – rare with metallized film due to self-healing; more common with film/foil
• Humidity ingress – moisture penetration through imperfect sealing

How to Test a Film Capacitor

1. Visual inspection – check for bulging, cracking, or resin damage
2. Capacitance measurement – use an LCR meter at the rated frequency
3. Insulation resistance – measure IR; a low value indicates dielectric degradation
4. DF / ESR test – high dissipation factor indicates aging
5. Withstand voltage test – for critical applications, verify with a hipot tester at reduced voltage

How to Read Film Capacitor Markings

Most film capacitors carry a code printed on the body, for example CBB21 104K 250V. Here is how to decode it:

• CBB21 – series designation (CBB = metallized polypropylene film)
• 104 – capacitance in pico-farads: 10 followed by 4 zeros = 100,000 pF = 100 nF = 0.1 µF
• K – tolerance, ±10%
• 250V – rated DC voltage

The capacitance code works the same for all film types: the first two digits are significant figures, the third digit is the number of zeros, and the unit is always pF. 473 means 47,000 pF = 47 nF; 222 means 2,200 pF = 2.2 nF.

Common Film Capacitor Series and Their Uses

Different series are designed for different jobs. This table shows the most common film capacitor series and where to use them:

Series	Dielectric	Typical Use
CBB21	Polypropylene	General pulse circuits
CBB22	Polypropylene	Switching power supplies
CBB60	Polypropylene	Motor run, AC circuits
CBB61	Polypropylene	Fan motor, small motors
CBB81	Polypropylene	High dv/dt snubber
CL11	Polyester	General purpose
CL21	Polyester	Coupling and bypass
X2	Polypropylene	EMI suppression (AC mains)

Two Real-World Selection Examples

Example 1: DC-link capacitor in a 10 kW solar inverter. A 10 kW three-phase solar inverter has a DC bus at 400-800 V with heavy ripple from the switching stage. Choose a polypropylene film capacitor rated 450 VDC (two in series derate the 800 V bus), with low ESR to handle the ripple current. A 40 µF / 450 V metallized polypropylene DC-link capacitor with screw terminals is typical for this class.

Example 2: Motor run capacitor in a 1 HP air conditioning compressor. A single-phase compressor motor needs a run capacitor to shift the phase of the auxiliary winding. Choose a CBB60 or CBB61 polypropylene capacitor rated at 450 VAC, with capacitance between 20-50 µF depending on the motor specification. Because the capacitor operates continuously, long-life construction and a sealed casing are essential.

FAQ

Q: What is the difference between a film capacitor and an electrolytic capacitor?
A: Film capacitors are non-polarized, have much lower loss, longer life, and better high-frequency performance, but lower capacitance density. Electrolytics offer high capacitance in a small package but are polarized and have limited life.

Q: Are film capacitors polarized?
A: No. Film capacitors are non-polarized and can be connected in either direction.

Q: What does “self-healing” mean?
A: When a local dielectric breakdown occurs in a metallized film capacitor, the thin metal electrode around the fault vaporizes, isolating the defect and allowing the capacitor to continue working.

Q: How long do film capacitors last?
A: With proper derating, 20+ years. Temperature and voltage stress are the main factors.

Q: Can I replace an electrolytic capacitor with a film capacitor?
A: Only when the circuit can accept a physically larger, non-polarized part with a lower capacitance value. On DC-link and power supply circuits, a film capacitor can often take the place of an electrolytic one.

Q: What is an X2 capacitor?
A: An X2 safety capacitor is built to suppress electromagnetic interference across the AC line, and is certified to EN/IEC 60384-14.

Need Help Choosing a Film Capacitor?

Xuansn is a film capacitor manufacturer. Our range covers CBB series, X2 safety capacitors, DC-link capacitors and motor run capacitors. Our engineers can supply samples and custom specifications matched to your application.

Send us your circuit parameters – voltage, capacitance, frequency and mounting – and we will come back with a recommendation within 24 hours.

The post Film Capacitor: Types, Working Principle, Applications & Selection Guide appeared first on Xuansn Capacitor.