154

In an AC application heat is generated within the capacitor

by both the AC component of the signal (which will depend

upon signal form, amplitude and frequency), and by the

DC leakage. For practical purposes the second factor is

insignificant. The actual power dissipated in the capacitor is

calculated using the formula:

P = I

E

Z

2

I = rms ripple current, amperes

R = equivalent series resistance, ohms

E = rms ripple voltage, volts

P = power dissipated, watts

Z = impedance, ohms, at frequency under

consideration

Using this formula it is possible to calculate the maximum

AC ripple current and voltage permissible for a particular

application.

2.2 MAXIMUM AC RIPPLE VOLTAGE

From the previous equation:

E

R

where P

for the product under consideration (see table).

However, care must be taken to ensure that:

1. The DC working voltage of the capacitor must not be

exceeded by the sum of the positive peak of the applied

AC voltage and the DC bias voltage.

2. The sum of the applied DC bias voltage and the negative

peak of the AC voltage must not allow a voltage reversal

in excess of that defined in the sector, ‘Reverse Voltage’.

2.3 MAXIMUM PERMISSIBLE POWER

DISSIPATION (WATTS) @ 25°C

The maximum power dissipation at 25°C has been calculated

for the various series and are shown in Section 2.4, together

with temperature derating factors up to 125°C.

For leaded components the values are calculated for parts

supported in air by their leads (free space dissipation).

The ripple ratings are set by defining the maximum tempera-

ture rise to be allowed under worst case conditions, i.e.,

with resistive losses at their maximum limit. This differential

is normally 10°C at room temperature dropping to 2°C at

125°C. In application circuit layout, thermal management,

available ventilation, and signal waveform may significantly

affect the values quoted below. It is recommended that

temperature measurements are made on devices during

operating conditions to ensure that the temperature differential

between the device and the ambient temperature is less than

10°C up to 85°C and less than 2°C between 85°C and 125°C.

Derating factors for temperatures above 25°C are also shown

below. The maximum permissible proven dissipation should be

multiplied by the appropriate derating factor.

For certain applications, e.g., power supply filtering, it may

be desirable to obtain a screened level of ESR to enable

higher ripple currents to be handled. Please contact our

applications desk for information.

2.4 POWER DISSIPATION RATINGS

(IN FREE AIR)

TAR – Molded Axial

SECTION 2:

AC OPERATION — RIPPLE VOLTAGE AND RIPPLE CURRENT

2.1 RIPPLE RATINGS (AC)

Case

Max. power

size

dissipation (W)

Q

0.065

R

0.075

S0.09

W

0.105

Temperature

derating factors

Temp. °C

Factor

+25

1.0

+85

0.6

+125

0.4

Case

Max. power

size

dissipation (W)

A0.09

B0.10

C

0.125

D0.18

Temperature

derating factors

Temp. °C

Factor

+20

1.0

+85

0.9

+125

0.4

TAA – Hermetically Sealed Axial

Case

Max. power

size

dissipation (W)

A

0.045

B0.05

C

0.055

D0.06

E

0.065

F

0.075

G0.08

H

0.085

J0.09

K0.1

L0.11

M/N

0.12

P0.13

R0.14

Temperature

derating factors

Temp. °C

Factor

+25

1.0

+85

0.4

+125

0.09

TAP/TEP – Resin Dipped Radial

TAP/TEP Technical Summary and

Application Guidelines