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Technical Information of Plastic Film Capacitors

编辑:Admin 时间:2015/8/6 21:55:27

Film capacitors, plastic film capacitors, film dielectric capacitors, or polymer film capacitors, generically called “film caps” as well as power film capacitors, are electrical capacitors with an insulating plastic film as the dielectric, sometimes combined with paper as carrier of the electrodes.

Terminologies

1 .Upper Category Temperature

The highest environmental temperature determined by capacitors  design and in which capacitor may continuously work.

2.Lower Category Temperature

The lowest environmental temperature determined by capacitors design and in which capacitor may continuously work.

3.Rated Temperature

The highest environmental temperature in which capacitor applied continuously with the rated voltage.

4.Rate Voltage (UR)

The maximum DC. voltage or peak value of pulse voltage that can be applied continuously to capacitor at any temperature between lower category temperature and rated temperature.

5.Category Voltage (Uc)

The maximum voltage that can be applied continuously to capacitor at upper category temperature.

6.Temperature Derated Voltage

The maximum voltage that can be applied continuously to capacitor at any temperature between rated temperature and upper category temperature.

7.Climatic category

The climatic category which the capacitor belongs to is expressed in three numbers separated by slashes,(IEC 60068-1:example 55/100/56)
55 – the lower category temperature (-55 C)
100 – the upper category temperature (+100 ‘C)
56 – days relevant to the damp heat test (56days).

8. Dissipation factor (tg 8)
The dissipation factor is ratio between reactive power of the impedance of the capacitor and effective power when capacitor is submitted to a sinusoidal voltage of specified frequency.

9.Temperature coefficient of capacitance
The change rate of capacitance with temperature measured over a specified range of temperature. It is normally expressed in parts per million per Celsius degree (10″5°C ) and referred to 20°C.
图q

Ci: Capacitance at temperature Ti.
Co: Capacitance at temperature To(20+-2)°C.

10.Insulation Resistance(I.R.) / Time Constant (t)
The insulation resistance is the ratio between an applied DC. voltage and the resulting leakage current after a minute of charge. It is expressed in Mo. The time constant is expressed in seconds with the following formula:

t[s]=I.R.[MQ]xCn[uF]

In general, Insulation resistance is used for describing smaller capacitance capacitors’ insulation character, Time Constant for describing larger one’s (example: CN>0.33uF).

11.Self-healing (Only to metallized film capacitor

The metal coatings of the metallized film, which are vacuum-deposited directly onto the plastic film, have a thickness of only several tens nm. At weak points or impurities in the dielectric, a dielectric breakdown would occur. The energy released by the arc discharge in the breakdown channel is sufficient to totally evaporate the thin metal coating in the vicinity of the channel. The insulated region thus resulting around the former faulty area will cause the capacitor to regain its full operation ability.

Applications and Typical graphs

1. Typical Properties

Polyester Film

• Very wide operating temperature range

• High dielectric constant

• Excellent self-healing properties

• Very good ratio box size/capacitance

• Good stability

Polypropylene Film

• Very low dissipation factor

• Very low dielectric absorption

• Very high insulation resistance

• Good behaviour in frequency

• Excellent self-healing properties

• Very good stability

2. Typical Applications

Polyester film capacitors
• Blocking and Coupling
• By-passing
• Decoupling
• Filtering
• Timing
• Low pulse circuits
• Oscillator circuits

Polypropylene film capacitors

• High frequency,pulse applications
• High current
• AC. applications
• Timing with high stability
• SMPS and TV set.
• Lighting
• Industrial
• Filtering high Q

Caution items in using plastic film capacitors
1 .Operation voltage
The plastic film capacitor varies in the maximum applicable voltage depending on the applied voltage waveform, current waveform frequency, ambient temperature (capacitor surface temperature), capacitance value ,etc. Be sure to use capacitors within the specified values by checking the voltage waveform, current waveform, and frequency applied to them (In the application of high frequency, the permissible voltage varies with the type of the capacitor. For
detail see the specification).CL21X,MKP25,MKP27 series isn’t suitable for AC applications.

2.operating Current

The pulse (or AC) current flowing through the capacitor is expressed as: I=deV/dt.
Due to the fact that dissipation factor of the capacitor will generate the internal heat under the application of high frequency or high pulse current, temperature rise in it will occur and may cause deterioration of withstanding voltage, even lead to break down (smoking or firing).Therefore, the safety use of capacitor must be within the rated voltage(or category voltage)and the permissible current.

The operating current must be considered by dividing into pulse current(peak current)and continuous current (rms current) depending on the break down mode, and when using, should make sure the both currents are within the permissible values.

Under the application of high frequency or high pulse ,we recommend to use the polypropylene film capacitor or C24 stacked capacitor.

3.Calculation of rms in various waveforms.

4.Capacitor for electromagnetic interference suppression of AC power supply

4.1 When using a capacitor across-the-line as means for prevention of noise, not only the supply voltage is always applied, but also abnormal surge such as lighting is applied, which may lead to smoking or firing. Therefore, the across-the-line capacitor is strictly regulated in safety standard in each country. Please use those approved products type MKP63, MKP62, C8862, which conform to corresponding safety standards of different countries.The DC capacitor will not be used in across-in-line circuit.

4.2 Capacitor for electromagnetic interference suppression of AC power supply (Class X)

It is suitable for being used in situation where failure of the capacitor could not lead to danger of electric shock, classified as class X1 andX2 (refer to the table below)

4.3 Capacitor for electromagnetic interference suppression of AC power supply (Class Y)
It is suitable for being used in situation where failure of the capacitor could lead to danger of electric shock, classified as class Y1,Y2 and Y4 (refer to the table below)

5.Charging and discharging

Because the charging and discharging current of capacitor is obtained by the product of voltage rise rate(dv/dt)and capacitance, low voltage charging and discharging may also cause deterioration of capacitor such as shorting and open due to sudden charging and discharging current. When charging and discharging, pass though a resistance of 20ohm/V to 1000ohm/V or more to limit current.

When connecting multiple film capacitors in parallel in withstand voltage test or life test, connect a resistance of 20ohm/V to 1000ohm/V or more in series to each capacitor.(For detail see the specification).

6.Buzzing noise

Any buzzing noise produced by capacitor is caused by the vibration of the film due to the coulomb force that is generated between the electrodes with opposite poles.lf the wave-form with a high distortion rate or frequency is applied accorss the capacitor,the buzzing noise will become louder.But the buzzing noise is of no damage to capacitor.

7. Surface overtemperature (T)

7.1 When capacitor is used in A.C. or pulse applications, the current that flows through the capacitor makes it heat up. If the capacitor heats up too much it might deteriorate causing a short circuit or fire. The limits described in the catalogue are not exceeded and it’s necessary to check temperature on the capacitor when it’s working. 7.2 Method for determining the surface overtemperature of the capacitor is showed in fig.1. The capacitor being tested must be supplied by A.C. or pulse voltage and frequency.

9. Special working conditions

9.1 Humid ambient.

It used for a long time in a humid ambient,the capacitor might absorb humidity and oxidize the electrodes causing breakage of the capacitorlf case of AC application,high humidity would increase the corona effect.This phenomenon case a drop in the capacitance value.ln case of working condition in AC application more severe than following table,please contact our engineers for detailed informations.

9.2 Resin

If the capacitor is placed in resin,the following situations might occur:

a. The solvent contained the resin might deteriorate the characteristics
of the capacitor;
b. The heat generated during the polymerization might damage the
capacitor.

9.3 Adhesive curing oven

Insert leaded parts only after the adhesive curing process of SMD parts,because the high temperature in curing oven will damage the capacitor.lf leaded parts must be fixed before the SMD gluing process ,please estimate if the curing temperature is suitable for leaded parts.

10.Soldering suggestions

In order to obtain a good solderability,we suggest to observe the following rules.

10.Max soldering temperature

Solder within the conditions mentioned in the following diagram.
图2

10.2 If re-working or dipping twice in necessary, it should be done after the capacitor returned to the normal temperature.

10.3 Insert leaded parts only after the adhesive curing process of SMD parts,because the high temperature in curing oven will damage the capacitor.” leaded parts must be fixed before the SMD gluing process ,please estimate if the curing temperature is suitable for leaded parts.

10.4 Avoid reflow soldering by combining the lead type with SMD parts.

11. Storage conditions:

11.1 It must be noted that the solderability of the terminals may be deteriorated when stored in an atmosphere filled with moisture, dust, or a reactive oxidizing gas.(hydrogen chloride, hydrogen sulfide, sulfuric acid,etc.)

1 1.2 It shouldn’t be located in particularly high temperature and high humidity, it must submit to the following conditions(unchanging primal package):
Temperature: not exceeding 35 °C
Humidity: not exceeding 80% RH

Storage time for tinned lead wire: (from the date marked on the capacitor’s body or the label glued to the package)
Bulk: <=24 months
Taping and line up: <=12 months

11.3 SMD storage suggestion

When unchanging a M38 (Moisture Barrier Bag) Class 1,stored in a temperature lower than 35°C and relative humidity lower than 80%, the storage is 12 months. After the opening of the M88, stored in a temperature lower than 30°C and relative humidity lower than 60% , the storage is 168 hours. If the reel is partially used, We recommends the recycle of the same M88 or a storage in areas with controlled temperature and humidity.

When placing an order or inquiring sample,
please specify the following, as much as you can.
1.Rated voltage: DC, AC.
2.Capacitance value and capacitance tolerance: J, K, M etc.
3.Finished product: Color TV, Monitor, Switching power, light, ballast, transducer,ADSL,UPS etc.
4.Application or circuit diagram: DC circuit, AC pulse circuit(S-shape correction, horizontal resonance circuit, peak absorption circuit), interface noise suppression circuit, high stability circuit
DC-link,DC-filter,PFC etc.
5.Condition of operation: pulse peak, frequency, waveform, current etc.
6.operating temperature.
7.Dimensions: body, lead space, etc.
8.5hape: enclosure(dip, case, etc), lead wire(straight, crimped, taping etc).
9.Sofety: Influence to the other component, when the capacitor gets
short-circuited or open. Influence to the capacitor, when the other
component or the circuit works irregularly.
10.Welding condition:SMD or tinned-Iead-wire type.
11 .Fixed stylezPCB,insuloted lead wire etc.