SMPS Capacitors
SMPS Capacitor Applications
FOREWORD
High speed switch mode power supplies place high
demands on the capacitors used in the input or output filters
of Resonant DC-DC or Pulse Modulated DC-DC converters.
AVX Corporation has developed several multilayer ceramic
(MLC) capacitor styles for these switcher applications. These
capacitors have been extensively tested and characterized
and found to have almost ideal performances to meet the
stringent requirements of these applications.
Output Filter Capacitor
The output from the switching circuit of a Switcher consists
of current on and off. From an elevated DC reference, this
current is an AC ripple additive on the DC. In order to smooth
this ripple effect, a filter circuit (usually inductive input) is built
to allow a storage of energy to take place during the rising
ripple portion and to allow a discharge of energy during the
falling ripple portion.
The ESR and ESL of the capacitor contribute to the net ripple
effect. The output filter capacitor is chosen for ESR, and with
previous types of capacitors, multiples were used in an
attempt to lower the net ESR. The MLC offers ESRs well
below the minimum allowable to lower noise levels, thus
eliminating the need for multiple units.
Input Filter Capacitor
The Input Filter capacitor is required to perform two functions:
To supply an unrestricted burst of current to the power supply
switch circuitry and to not only do it without generating any
noise, but to help suppress noise generated in the switch
circuitry. It is, in effect, a very large decoupling capacitor. It
must have very low ESL, capabilities for very high dv/dt, as
well as di/dt and it must have a very low ESR to eliminate
power loss.
The distance from the primary DC source, as well as the type
of capacitor used in this source (usually electrolytics),
presents a very high inductance to the input of the Switcher.
The MLC input capacitor, with its excellent ESL and ESR
characteristics, is located physically close to the switch
circuitry. Repetitive peak currents, inherent with the Switcher
design, require a high ripple capability, as well as high surge
capability for transients, both induced and conducted from
other sources. MLCs have both these capabilities.
Other MLC Capacitors for
SMPS Applications
AVX also manufactures coupling, decoupling, resonant and
snubber capacitors for SMPS applications. Contact AVX for
Application Specific S.M.P.S. capacitor requirements.
Olean, NY, USA
716-372-6611
Coleraine, Northern Ireland
++44(0) 28703 44188
St. Apollinaire, France
++33(0) 38071 7400
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AVX [ AVX CORPORATION ]
