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135D277X0015T2 Datasheet(PDF) 10 Page - Vishay Siliconix |
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135D277X0015T2 Datasheet(HTML) 10 Page - Vishay Siliconix |
10 / 14 page 135D www.vishay.com Vishay Revision: 09-Apr-13 10 Document Number: 40024 For technical questions, contact: tantalum@vishay.com THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT ARE SUBJECT TO SPECIFIC DISCLAIMERS, SET FORTH AT www.vishay.com/doc?91000 GUIDE TO APPLICATION 1. AC Ripple Current: Subjecting a capacitor to an AC voltage causes an AC current to flow through it. The amplitude of the current is dependent on the impedance of the capacitor at the frequency of the applied signal: where: I = Ripple current V = Applied AC voltage Z = Impedance of capacitor (frequency dependent) This current causes heating in the capacitor because of I2R losses (R is the equivalent series resistance at the applied frequency). This heating or power dissipation, is one of the limiting factors of the capacitor’s ripple current rating. These power dissipation ratings are based on a calculated + 50 °C internal temperature rise in still air. The maximum allowable ripple currents given in the Standard and Extended Ratings tables are based on these ratings and the maximum equivalent series resistance at that frequency. The relationship is written as follows: where: P = Maximum power I = Maximum ripple current R = Equivalent series resistance Therefore: where: R is in P is in W I is in ARMS 2. AC Ripple Voltage: In operation, the peak voltage across the capacitor (DC working voltage plus peak ripple voltage) must not exceed the rated working voltage of the capacitor. The DC component of the applied voltage should be sufficiently large to prevent polarity reversal in excess of 3 V at + 85 °C or 2 V at 125 °C. There will be a point at the lower frequency and capacitance values when the peak AC voltage will be the limiting factor on the ripple current - not its heating effects. For example: Given a 25 μF, 8 V capacitor in the “C” case code and assuming a ripple current application at a frequency of 120 Hz, the total maximum allowable peak to peak voltage at + 25 °C is: In order to allow the full swing of 11 Vpp and not exceed rated forward or rated reverse, a DC bias of 2.5 V is assumed to be applied. From the ”Standard Ratings Table”, the maximum ripple current at 40 kHz is 0.820 A. Compensating for the lower frequency from the “Ripple Current Multipliers” tables: This current rating is calculated strictly on the basis of maximum power dissipation. Now calculate what impressed voltage this amount of current will cause across this capacitor. Assuming a sinusoidal voltage, calculate the rated peak to peak current: where: ESR = 4 (from “Standard Ratings” table) Therefore: and Therefore, the peak voltage of the capacitor is the limiting factor for the ripple current and can be calculated as follows: or CASE CODE MAXIMUM PERMISSIBLE POWER DISSIPATION AT + 25 °C (W) IN FREE AIR C1.00 F1.55 T1.75 K1.95 I V Z --- = PI 2 R = I P R ---- = 8 V F + 3 VR 11 V pp = I RMS (120 Hz) 0.820 A x 0.6 0.492 A RMS == I pp I RMS x 2 2 0.492 x 2.828 1.39 A pp = = = V pp impressed I pp x ZC 120 Hz = Z C120Hz ESR 2 (X C(120 Hz) + 2 = X C 1 2 fC 1 2 120 25 x 10 -6 53.1 == = Z C 4 2 53.1 2 + 53.3 = = V pp impressed 1.39 A pp x 53.3 = 74.1 V pp 11 V pp = Max. I pp V Cpp allowed Z C ----------------------------------------- 11.0 V 53.3 ------------------ 0.206 A pp = = = 0.206 22 --------------- 0.073 A RMS at 120 Hz = |
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