258

CG01-I

EMI LEADED FILTERS

EMI SUPPRESSION FILTERS

VARISTOR-CAPACITORS

DSS710 Series

The reason the 3-terminal structure provides excellent

high frequency characteristics.

Bypass capacitors should logically be able to remove

more noise as frequency increases. In actual fact, the

electrodes and lead wires of the capacitor have series

inductance as shown in Fig. 3, and this causes an LC

resonance when the frequency is between 1MHz and

50MHz. As a result, when the frequency is higher than

the self-resonance frequency, the noise suppression

capability of the bypass capacitor is drastically reduced

because the capacitor functions as inductor. To solve

this problem, the DSS series has one side of the capacitor

electrodes connected to two lead wires. This eliminates

the series inductance to the capacitor. Furthermore,

a ferrite bead is attached to each lead wire to form a

T-shaped filter, thus providing efficient noise suppression.

Appearance

Ferrite bead:

Absorbs high-frequency noise.

Varistor:

Bypasses high-voltage

surges to ground in order

to protect circuits.

Capacitor:

Bypasses high-frequency noise.

Symbol

12-22

223S

Conventional 2-Lead Capacitor

3-Lead Capacitor (DSS Series)

Fig. 3 Equivalent circuit

12-22

223S

M

M

3 -TERMINAL STRUCTURE

APPLICATIONS

NOISE ABSORPTION EFFECT OF

VARISTOR-CAPACITOR

Waveform when a

Varistor-Capacitor is

not used (surge from

a noise simulator).

Varistor-Capacitor

is used to suppress

the surge

shown below

Waveform after the

noise passes through

a Varistor-Capacitor.

Protection of circuitry

is achieved.

The Varistor-Capacitor is capable of removing even

1200V surges and will withstand 2000V impulses.

SCALE:

200V/Div.

10NS/Div.

Systems

Lines to be connected to

Effects

Engine Controllers

Power lines, I/O for

Protection of systems from excessive voltage. Prevents ignition noise,

low-frequency current

lightning surges, etc. from causing malfunctions.

Automobile

Power lines, audio

Protection of system from excessive voltage. Prevents ignition noise from

Audio Equipment

output lines

influencing audio current.

Computers

Power lines, I/O lines for

Protection of systems from excessive voltage. Prevents radiation and

low-frequency current

conduction noise.

DC Motors

Power lines

Prevention of brush noise.