Plastic Film Capacitors

2.2 Permissible current to operating frequency

The film capacitor varies in the frequency characteristic of the dissipation factor (tanδ) depending on the dissipation factor,

and hence the permissible rms current for operating frequency differs depending on the capacitor type. In particular, when

operating at high frequency, the dissipation factor (tanδ) increases, and when using over the permissible current, it may

include the thermal runaway, possibly leading to smoke or fire. Shown below are typical examples of permissible current

by frequency (rms value) of the ECQE(F) type using polyester film and ECWF(A) type using polypropylene film. For detail

inquire us by presenting the operating conditions, or make sure the own temperature rise of the capacitor and the capacitor

surface temperature are within the permissible range in the worst operating conditions.

2.3 The capacitance and the permissible currents

The permissible rms current varies with the capacitance value. The permissible current (rms) values by the frequencies

and by the capacitance of representative types are shown below. In actual use, inquire us for detail by measuring the

voltage and current waveforms, ambient temperature, and own temperature rise.

Type

: ECQE(F)(Polyester)

Type

: ECWF(A)(Polypropylene)

Rated voltage

: 250 V.DC ⇒

Rated voltage

: 250 V.DC ⇒

150 Vrms 60Hz (at sine wave)

125 Vrms 60Hz (at sine wave)

Operating temp. : -40 to 85

℃ (Cap. surface)

Operating temp. : -40 to 85

℃ (Cap. surface)

2.4 Permissible current to pulse current

・ When used in switching circuits or snubber circuits a momentary high current pulse may cause local heat generation.

This causing the capacitance value to deteriorate or an open circuit condition. Local heat generation may also induce

smoke or fire. The pulse permissible current (10000 times) isobtained by the product of dV/dt (V/μs) value that is

entering to the specification and capacitance (μF).

・ The dV/dt (V/μs) value of a film capacitor is determined by the element structure, and in the metalized type, in particular,

the internal evaporated electrode and external takeout electrode are connected by metalized contact (metal spraying),

and hence due caution is needed because the upper limit of dV/dt value is low.

・ The dV/dt values corresponding to rated voltage and capacitance value of representative types are shown in page 6.

When used in a high current pulse circuit, check the pulse permissible current (Ao-p).

Please contact with us, If pulses are applied more than 10,000 times.

＜How to determine pulse permissible current＞

When voltage V(V) is applied to capacitor C (F for farad), the electric charge Q(C) is expressed in formula

①.

Ｑ＝Ｃ・Ｖ ‥‥‥‥

①

The charging current I(A)flow in the capacitor at this time is expressed in formula

②.

I

＝dQ/dt ‥‥‥‥

②

Differentiating both sides of formula

① by timet and putting into formula ② yields formula ③.

dQ/dt = C

・ dV/dt

I = C

・ dV/dt ‥‥‥‥

③

Therefore, the pulse current is determined as theproduct of the capacitance value C (μF) and voltage change dV/dt

per μs.

(Example)

In the case of ECQE4224KF (permissible dV/dt)

Rated voltage

: 400 V.DC

Capacitance

: 0.22 µF

Permissible dV/dt value : 37

Pulse permissible current : 0.22(μF)×37 ≒ 8Ao-p

(however, number of repetitions is 10,000 times or less), that is, momentary pulse current can be used up to 8 Ao-p.

Make sure the rms current is within the permissible value.

2022/1/14

(Note)

The graphs illustrated

are for reference only.

Waveform of current

and temperature rise of

capacitor are key

factors to determine

permissible current. For

actual application,

consult our sales

representative or sales

office.

5.0

1.0

0.5

0.0

10

100

50

4.5

4.0

3.5

3.0

2.5

2.0

1.5

10.0μF

4.7μF

2.2μF

1.0μF

0.47μF

0.22μF

0.10μF

0.047μF

0.022μF

0.010μF

100

50

Frequency (

ｋHz)

Frequency (

ｋHz)