pulse capacitors Terms and definitions Pulse capacitor A pulse capacitor is a capacitor designed primarily for applications with intermittent charges and/or discharges at high values of the charge/discharge current. Pulse operation Capacitors subjected to pulses with fast rise or fall times (high dU/dt) will be exposed to high current pulses (i = C x dU/dt). In order not to overload the internal connections the current must be limited. The current limits for a specific type of capacitor are dependent upon: • Amplitude and form of the pulse • Rated voltage of the capacitor • Capacitance • Geometrical configuration of the winding At repeated pulse operation, self-heating, ambient temperature and cooling set the load limit. Pulse current limits are commonly expressed in the form of maximum permitted dU/dt in volts per microsecond. The figures stated in the data sheets refer to an unlimited number of pulses charging or discharging to or from the rated voltage UR. Typical applications PhE426 PhE429 single metallized films Pulse capacitors are intended for coupling, bypass, filtering, snubbering or pulse operation in SMPS at low as well as at high AC voltage of high frequency where there is a need for high pulse rise time and high ionization level, e.g. fly-back circuits in TV-sets. double metallized films PhE450 1 section dielectric films double metallized film single metallized polypropylene film PhE450 2 section polypropylene film Construction In a metallized film capacitor the electrodes are deposited under vacuum on the plastic film. Contact to the metallized layers is achieved by spraying the ends of the windings with a special metal alloy. This method results in low inductance and a low series resistance capacitor. There are three main types of metallized film compositions. In film/foil types of capacitors metal foils are used as electrodes. double metallized film PhE450 3 section polypropylene film metal foil electrodes Pfr polypropylene films metal foil electrodes PhE448 polypropylene films single metallized polypropylene film thermal dissipation The power dissipation in a capacitor is approximately: P = 2πf x C x tanδ x Urms2 (1) or P = tanδ/(2πf x C) x Irms2 (2) tanδ = dissipation factor. Typical values can be estimated from the diagram on page 15. f = frequency (Hz) This is valid for sine wave signals. For wide band signals, the power dissipation values for each frequency have to be added, i.e. Ptot = P1 + P2 + .... + Pn ∆T = (Th – Ta) = P x Rthha °C (3) Temperature increase between hot spot (Th) of the capacitor and ambient (Ta). Rthha = Thermal resistance (°C/W) between hot spot and ambient. Maximum permissible hot spot temperature for polypropylene is +105 °C and maximum ∆T=10 °C at +85 °C Ta. For lower Ta, a higher ∆T can be allowed. This is implemented in PCCAD software package below. The diagrams for derated AC voltage vs. frequency for the pulse capacitors in this catalogue are calculated with Ta = +85 °C and ∆T = 10 °C. Example: PHE450SB4680JR06 6.8 nF 2000 VDC f = 100 kHz, Urms = 200 VAC, DF = 0.03%, Rthha = 98 °C/W With formula (1) and (3) above: P = 0.05 W and ∆T = 5 °C If Ta = 85 °C then Th = 90 °C Pulse Capacitor CAD (PCCAD) - unique software In order to make it easy to select pulse capacitors Evox Rifa has developed a software for Windows™ with the following main options: • To get general technical information about pulse capacitors • To get complete data sheets of all Evox Rifa pulse capacitors • To select a Part Number and then get diagrams of ESR, DF, max lrms and Urms vs frequency and ambient temperature. This means that it is easy • To check if a certain capacitor is suitable for a certain application. • To make Fourier analysis of an arbitrary waveform. • To make print-outs of data files and diagrams from simulations. This is normally all the information needed to select the right pulse capacitor. Free download is available at www.kemet.com. pulse capacitors Quality tests and requirements The details are valid for all types of pulse capacitors unless specific remark is made in each detail specification. All tests are made at +23°C unless otherwise specified. TestIEC Publication ProcedureRequirements Voltage 60384-1 1.6 x UR proof clause 4.6 after 60 s The capacitors must withstand the voltage without breakdowns or flashovers and without decreased insulation resistance below the value in each detail specification. No visible damage. clause 4.6 2.3 2 x UR (min 400 VDC to case) after 60s As above Vibration 60068-2-6 Test Fc 6 h with 10 – 500 Hz and 0.75 mm amplitude or 98 m/s2 depending on frequency No visible damage. tanδ ≤ 1.2 x stated value at 100 kHz ∆C/C ≤ ± 0.5 % 60068-2-29 4000 bumps with 390m/s2 Bump Test Eb mounted on PCB ∆C/C ≤ ± 0.5% tanδ ≤ 1.2 x stated value at 100 kHz Insulation resistance: ≥ 100000 MΩ for CR ≤ 0.33 µF ≥ 30000 s for CR > 0.33 µF Resistance 60068-2-20 Solder bath at + 260°C to soldering Method 1A ± 5°C with screening heat * Immersion of the terminations into the solder bath shall be completed in a time not exceeding 1 s and the terminations shall remain immersed to the specified depth for 10 + 1 s and then be withdrawn. ∆C/C ≤ ± 0.5 % tanδ ≤ 1.2 x stated value at 100 kHz No visible damage. Climatic 60384-1 IEC 60068-2.2 dry heat 16 h sequence para 4:21 IEC 60068-2-34 damp heat, one cycle, IEC 60068-2-1 Test Aa 2 h Insulation resistance: ≥ 100000 MΩ for CR ≤ 0.33 µF ≥ 30000 s for CR > 0.33 µF ∆C/C ≤ ± 0.5 % tanδ ≤ 1.2 x stated value at 100 kHz Damp heat IEC 60068-2-3 + 40°C and 90 – 95% RH steady state Test Ca 56 days No visible damage. Insulation resistance: ≥ 50000 MΩ for CR ≤ 0.33 µF ≥ 15000 s for CR > 0.33 µF ∆C/C ≤ ± 1% tanδ ≤ 1.2 x stated value at 100 kHz Endurance, AC 1000 h at +85°C and 1.25 x UR AC No visible damage. ∆C/C ≤ ± 3% tanδ ≤ 1.5 x stated value at 100 kHz Insulation resistance: ≥ 100000 MΩ for CR ≤ 0.33 µF ≥ 30000 MΩ for CR > 0.33 µF Charge and 60384-17 10000 pulses and with discharge para 4.13 (2 x) dU/dt according to detail specification tanδ (100 kHz) ≤ 2 x stated value (100 kHz) ∆C/C ≤ ± 0.5% Insulation resistance: ≥ 50000 MΩ for CR ≤ 0.33 µF ≥ 15000 s for CR > 0.33 µF * Note: Generally, all small polypropylene capacitors are sensitive to the soldering heat due to the relatively low melting point of polypropylene material (160°C - 170°C). This is why the suitability of the soldering process should be checked before the use of especially PHE426 in 5 and 7.5 mm pitches. Consult KEMET for recommended temperature profiles. Evox Rifa Leaded Film Capacitors 95