EMI LEADED FILTERS
EMI SUPPRESSION FILTERS
VARISTOR-CAPACITORS
DSS710 Series
NOISE ABSORPTION EFFECT OF
3-TERMINAL STRUCTURE
VARISTOR-CAPACITOR
Appearance
Symbol
12-22
223S
M
SCALE:
200V/Div.
10NS/Div.
Ferrite bead:
Absorbs high-frequency noise.
Waveform when a
Varistor-Capacitor is
not used (surge from
a noise simulator).
Varistor:
Bypasses high-voltage
surges to ground in order
to protect circuits.
Capacitor:
Bypasses high-frequency noise.
Varistor-Capacitor
is used to suppress
the surge
The reason the 3-terminal structure provides excellent
high frequency characteristics.
shown below
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.
12-22
223S
M
Waveform after the
noise passes through
a Varistor-Capacitor.
Protection of circuitry
is achieved.
3-Lead Capacitor (DSS Series)
Conventional 2-Lead Capacitor
The Varistor-Capacitor is capable of removing even
1200V surges and will withstand 2000V impulses.
Fig. 3 Equivalent circuit
APPLICATIONS
Systems
Lines to be connected to
Effects
Power lines, I/O for
low-frequency current
Protection of systems from excessive voltage. Prevents ignition noise,
lightning surges, etc. from causing malfunctions.
Engine Controllers
Automobile
Audio Equipment
Power lines, audio
output lines
Protection of system from excessive voltage. Prevents ignition noise from
influencing audio current.
Power lines, I/O lines for
low-frequency current
Protection of systems from excessive voltage. Prevents radiation and
conduction noise.
Computers
DC Motors
Power lines
Prevention of brush noise.
258
CG01-I
MURATA [ muRata ]
