Plastic Film Capacitors

(Example) Derating of rated voltage to operating temperature. Rated upper limit temperature 85

℃,

Upper category temperature 105

℃, Derating of rated voltage to which is 1.25 %/℃ at more than 85 ℃

1.3 Permissible voltage (R.M.S) in current corresponding to DC Rated voltage

・ A noise suppression capacitor ( AC rated voltage) should be used at the primay side power supplies.The design which

premised on use by 50Hz or 60Hz sine wave.

・ In case of applying voltage in alternating current (50Hz or 60Hz sine wave) to a capacitor, permissible voltage(R.M.S).

The capacitor of DC rating should not be used at the primary side power supplies.

1.4 Derating of rated voltage when using at high frequency

When using at high frequency, there is a risk of thermal runaway (smoke, fire) due to self heat generation in the capacitor.

Derate the operating voltage according to the example below.

For use at high frequency, we recommend ECHU(X)/(C), ECWF(A)/(L), and ECWH(A)/(C)/(V) types.

＜Derating example of operating voltage＞

Capacitor used

: ECWF2154JA (250 V.DC, 0.15 μ

Ｆ)

Operating frequency

: 40 kHz (sine wave)

Permissible current (entry the value from specification) : 40 kHz 2.0 Arms

Therefore, the operating voltage at sine wave 40 kHz is lower than to 53 Vrms (derating ratio 58%), as

compared with AC permitted voltage of 125 Vrms at commercial frequency.

(It is necessary to derate until the self heating temperature rise of the capacitor is below the specified value.)

〈Caution〉

(1) Use the peak value (Vo-p) of the Pulse voltage applied between the both terminals of the capacitor within the

DC rated voltage.

(2) When using at high frequency, it may lead to breakdown due to withstand voltage deterioration by self heat

generation. Therefore, measure the self heating temperature rise value of the capacitor, and make sure it is within

the specified.

(3) Protection for safety should be required in the case of the voltage over the rated voltage (permitted voltage) may

be applied to the capacitor due to abnormal action such as trouble elsewhere in the circuit.

Film capacitors are low in internal impedance, and hence a very large current may flow depending on the circuit. In particular,

when turning power switch on and off, make sure a very high pulse current may flow.

When a current exceeding the permissible range flows into capacitor, this can cause the capacitance value to deteriorate or

an open circuit condition, temperature rise occurs due to self heat generation, this cause can deterioration of withstand

voltage and result in short circuit, possibly leading to smoke or fire.

In the application, make sure current is within permissible current or self heating temperature is within permissible self

heating temperature rise limit shown on each delivery specifications.

2.1 Permissible current

The permissible current must be considered by dividing into pulse current (peak current) and continuous current

(rms current) depending on the breakdown mode, and when using, therefore, make sure the both currents are within the

permissible values.

2. Permitted current

2022/1/14

V =

=

= 53 Vrms

2.0

2

×3.14×40×103×0.15×10-6

I

2πfC

Cap. Surface Temp.(℃)