Film capacitors

Film capacitors —an indispensable part of passive element base of any electronic device. They can be the best decision in case of high-frequency pulse current using. The field of application is extremely wide.

Film capacitors specific features:

• Good self-healing properties;
• High thermal stability;
• High stability of key electric characteristics at applied voltage changing;
• Low ESR and high alternating-current-carrying capacitance (in such a case the self-heating effect decreases;)
• Mechanical and electrical characteristics of capacitors MKT and MKP series satisfy requirements of branch standards IEC 60384-2, IEC 60384-16 and IEC 60384-14.

Field of application of Epcos film capacitors and recommendations for choosing:

• EMC Filters

  In order to be applied in EMC Filters the capacitors must have certificates of X2 and Y2 classes corresponding the international standards.
  The capacitors of B32021...B32026 series satisfy the requirements of Y2 certificate. The values of capacitance are up to 1 μF and lead spacing is 37,5 mm. Compact effective capacitors series B32921…B32928 satisfy X2 class, the capacitance is up to 45 μF.
  In case when maximal voltage capability or reinforced insulation are required it is recommended to use seriesB32911…B32916 (X1) or B81123 (Y1).

• DC circuits

  Capacitors are used in DC devices in order to stabilize DC voltage at the output of AC/DC-converters that prevents the voltage drop at in-rush current in the load.
  In many cases film capacitors are connected in parallel with Aluminum electrolytic capacitors, as thanks to high current-carrying capacitance and low stray inductance they provide the filter operation at more high frequencies.
  MKP capacitors are assigned for operation in a wide range of working voltage (series B32774…B32778 — with high specific capacitance, series B32674…B32678 — large power).
  These series cover the capacitance range up to 200μF and have lead spacing 27,5…52,5 mm. Such capacitors are able to withstand continuous operating voltage from 450 to 1300 V (DC).Maximal working temperature comes to +105°C.
  At lower voltage values(up to 630 V (DC)) or at higher temperatures (up to +125°C) MKT-capacitors are applied (seriesB32520…B32529) are characterised by higher capacitance up to 220 μF in comparisson with MKP-capacitors.

• Power Factor Correction (PFC)

  The task of PFC-modules is to increase constant voltage after rectifier units and to compensate the reactive Power component being generated in switching power supply. The capacitors used in such devices must withstand both continuous voltage and applied pulse voltage at high frequency. This fact should be taken into a consideration when choosing capacitors for PFC in order to avoid overload during operating.
  For this aim as addition to MKT capacitors of general application (seriesB32520…B32529) and their modifications with epoxy coating (series B32591…B32594), polypropylene capacitors were developed (series B32671Z…B32673Z) satisfying requirements for PFC-modules. They are perfectly suitable for operating in circuits with high harmonics. Thanks to high maximal working temperature +110°C capacitors of these series are able to withstand the most intensive regimes in any switching power supplies.
  New MKP-series B32611P4…B32613P4 (450 V (DC) are up to 2,2 μF, powder epoxy coating) with compact dimensions, high pulse current and low level of acoustic noise was especially developed for application in switching power supplies. Also another variant of this series is being produced (B32671P4…B32673P4).
  If high capacitance values are required it will be better to use series B32774…B32778 with high specific capacitance B32674…B32678 with high power.

• DC/DC-converters

  A current in DC/DC-converters flowing through a capacitor has different values in dependence to converter's topology. Required ratio current/ frequency for capacitors in down/step-up converters is lower than in flyback or resonance transformers.
  If requirements to a current are not very critical one can use MKT-capacitors B32529…B32526 with voltage up to 630 V (DC) or MKP-capacitors B32774…B32778 with voltage (up to 1300 V (DC)). Both types have high specific capacitance.
  Other series of capacitors with high power level B32671Z…B32673Z (up to 2,2 μF) and B32674…B32678 (up to 60 μF) withstand high current at assigned frequency.
  At very high values of current and big impulses it is necessary to use snubbering and resonant capaсitors described below.

• Snubbering/resonant circuits

  Snubbering capacitors are being connected in parallel with semiconductor devices for reducing of big voltage surges which appear when switching at high frequency. Snubbering capacitors are used in such devices as DC/DC-converters, PFC-modules and inverters.
  Resonant capacitors must withstand continuous (generally sinusoidal) AC voltage of high frequency and have stability to overloading.
  The stability to heating and big impulses are the key characteristics of snubbering and resonant capacitors. They are important when developing devices. MKP-capacitors B32651…B32656 are suitable for snubbering and resonant circuits in a best way: they are charecterised by ability to self-heating (rms) and by variety of pin leads (for example, leads designed for mounting in wholes and strap terminals for using in IGBT). One can use the series B32671L…
  If high sensitivity to pulse voltage is required following capacitors will be suiatable B32632… B32634 and B32686S, which are able to withstand the speed of voltage increasing up to 20 000 V/μs, very high values of a current (rms) and frequency higher than 100 kHz.
  At present moment the company produces 17 variants of leads performance for snubbering series. All components are suitable for operating at high temperatures up to 110°С.
  In 2015 Epcos represented film capacitors with double-sided metallization for applications where the high current withstandability is a key characteritic MMKP B32641/ B32642. Components can be used in resonant circuits, electronic ballasts, high frequency devices with high values of current, power supplies,etc.
  In 2015 TDK (Epcos) represented new online programm for choosing of snubbering capacitors. The programm allows sufficiently simplify the process of searching of components applied in order to protect IGBT from voltage surge. When using the program a researcher can enter only the IGBT code in search window. Integrated database distinguishes IGBT being produced by more than 100 leading companies. The search can be realized also by key parameters (voltage, capacitance, leads performance). One can use this program on TDK web page (Epcos).

• Filtering of ouptut AC voltage

  The main application of output filters is a protection of a load from high frequency components appearing in converter and from current surges. In order to avid such problems it is recommended to use capacitors B32794…B32798 with capacitance values up to 75 μF and operating voltage up to 400 V (AC).
  Higher withstand ability to pulse voltage series B32651…B32656 provides. dV/dt value reaches 8000 V/μs. The series also demonstrates good characteristics on self-heating at high frequencies.

• Filtering in output rectifiers

  In general output rectifiers are half wave. They convert AC voltage to DC voltage. Positive half-wavelength of rectified voltage is further being used in order to form voltage for welding. The suppression of high frequency components is provided by a capacitor being connected to a rectifier's output.
  For this aims EPCOS offers power capacitors B32674…B32678 and also new series B32794…B32798 with a wide range of nominal voltage 250…400 V (AC) or 630…1050 V (DC)) and capacitance up to 75 μF.
  Alternative series B32651…B32656 has a higher current-carrying capacitance; capacitance values up to 8.2 μF , lead spacing 37,5 mm and nominal voltage up to 2000 V (DC).
  Also this capacitors have such important characteristics for this application as large speed of volage increasing dV/dt (up to 8000 V/μs) and very low level self heating at high frequency.

• Potential dividers

  Capacitors in potential dividers are being connected in series. The main requirement to such capacitors is to provide very high capacitance stability to humidity and temperature variations.
  In such conditions X2 miniature film capacitors, (for example B3292*C/D) do not suit.
  In such a case a new series of MKT film capacitors has been developed. The series B32931…B32936 is able to operate at hard service conditions and suitable for electrical meters.
  Such series have a long useful life and very low capacitance losses. Even after 1000 hours of testing at +85°°C, 85% relative humidity and 240 V (AC) a maximal shifting of capacitance is lower than 10%. Series B32931…B32936 covers a capacitance range from 0,047 to 10 μF and has a nominal voltage 305 V (AC). A maximal working temperature of these capacitors is about +105°C. As an addition, components with capacitance less than 2,2 μF have an X2 class Certificate of Conformance .
  In such a way capacitors of this series entirely correspond modern market requirements and have following advantages:
  • can work at high environment humidity
  • saves high capacitance stability at hard service processes
  • do not require increasing of components sizes
  in devices
  •have a sufficiently smaller dimensions comparing to other technical solutions saving the same reliability
  • correspond the requirements of a main standard for
  capacities IEC/UL 60384-14 (up to 2,2 μF).

Characteristics of film capacitors

Series		Technical characteristics	Features	Type
X2		Vrms: 305 V (AC) CR: 10 nF... 45 μF	X2 Class (2500 V) for interference suppression correspond international standards Lead spacing 10...52,5 mm	B32921C/D ... B32926C/D B32923E/F... B32928E/F
X1		Vrms: 330/340 V (AC) CR: 10 nF... 6,8 мкФ	X1 Class (4000 V) for interference suppression Correspond international standards "Across the line" applications Lead spacing 10...37,5 mm	B32911... B32916
Y2		Vrms: 300 V (AC) CR: 1nF... 1 μF	Y2 Class (5000 V) for interference suppression Correspond international standards "Line to ground" applications Lead spacing 10...37,5 mm	B32021... B32026
Y1		Vrms: 250 V (AC) CR: 1...10 nF	Y1 Class (8000 V) for interference suppression Correspond international standards "Line to ground" applications Lead spacing 15...22,5 mm	B81123
MKT for large current capability		Vrms: 305 V (AC) CR: 47 nF... 10 μF	+85°C/85% relative humidity/1000 hours /240 V (AC) X2 safety class for UL/IEC (C≤2,2 μF) High capacitance stability	B32932... B32936
MKP AC filtration		Vrms: 250...400 V (AC) CR: 0,82...75 μF	Working temperature up to +105°C Output alternating voltage filtration Optimized AC voltage performance at small dimensions High ripple current/frequency capability	B32794... B32798
MKP for output AC filtering		Vrms: 450...1300 V (DC) CR: 1,5...200 μF	Capacitance values up to 110 μF Working temperature up to +105°C Useful life 100 000 hours at 1∙VR,+70°C 4-pin version for high mechanical strength 2-pin and 4-pin versions Lead spacing 27,5...52,5 mm	B32774... B32778
		Vrms: 300...875 V (DC) CR: 0,47...60 μF	This series is characterised by large Power: higher current capability comparing with B3277x series Working temperature up to +105°C Useful life is about 100 000 hours at 1∙VR,+70°C 4-pin version for high mechanical strength 2-pin and 4-pin versions Lead spacing 27,5...52,5 mm	B32674... B32678
MKT for DC circuits and DC filtration		Vrms: 63...630 В (DC) CR: 1 nF...220 μF	For low voltage DC circuits Operating temperature up to +125°C Useful life 200 000 hours at 1∙VR,+70°C	B32520... B32529
MKP общего назначения		Vrms: 250...2000 В (DC) CR: 1 nF...8,2 μF	For Snubbering, resonant circuits B3267xL for pulse and gigh frequency loads Working temperature up to +105°C Operating both in AC and DC circuits Big speed of voltage increasing (dV/dt) and high AC current capability Lead spacing 10…37,5 mm	B32651... B32656 B32671L... B32672L
MKP for PFC		Vrms: 450...630 V (DC) CR: 0,01...2,2 μF	Working temperature up to +105°C Special version for PFC-modules Lead spacing 10…22,5 mm	B32671Z... B32673Z
		Vrms: 450 V (DC) CR: 100 nF... 2,2 μF	Working temperature < up to +105°C Special version for PFC-modules operating at 450 V (DC)	B32611P4... B32613P4 B32671P4... B32672P4
MFP		Vrms: 330...3000 V (DC) CR: 1...33 nF	For snubbering and resonant circuits Big values of dV/dt and frequency in case of MFP-technology Working temperature up to +110°C Lead spacing 15…37,5 mm	B32632... B32634 with epoxy coating
				B32686A корпусные
MKP snubbering		Vrms: 850...2000 V (DC) CR: 0,047...3,3 мкФ	For snubbering and resonant circuits Strap terminals for using in IGBT Working temperature up to +110°C Useful life 200 000 hours at nominal voltage	B32656S
MFP snubbering		Vrms: 1000...2000 V (DC) CR: 22...680 nF	For snubbering and resonant circuits Big values of dV/dt and frequency in case of MFP-technology Strap terminals for using in IGBT working temperature up to +105°C Useful life 200 000 hours at nominal voltage	B32686S

A short review on film capacitors EPCOS   

Ordering code structure

Film capacitors as well as other Epcos components are being indentified by unique type which is the same os ordering code. The code consists of 15 symbols and includes 3 data groups. Each group strarts from a symbol. Then a number goes. The structure of Epcos code for film capacitors is depicted on the figure below.