wilmer companioni - kemet webinar -- capacitor application ......microsoft powerpoint - wilmer...

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Capacitor Fundamentals

Low Voltage DC Applications

© 2017 KEMET Corporation

Component

Solutions

Market

Segment

Dielectric &

Products

System Solutions

Design Discipline

Circuit

Application

Selecting the Right Component


What is Low Voltage DC?

Consumer Industrial Computing Telecoms Automotive Medical Mil/Aero


Trends

http://www.futuretimeline.net/subject/computers-internet.htm

http://magazine.sfpe.org/issue-73-effects-radiant-heat-flux-clean-agent-performance-class-c-fires

1.Mark Owen et al. “Datacom Equipment Power Trends and Cooling Applications”, ASHRAE Datacom Series, ASHRAE, Atlanta, GA, 2012.


Capacitor FundamentalsParasitics


Electrode Plates Dielectric

The value of a capacitor is measured in farads. For 1 farad of capacitance, 1 coulomb of charge is stored on the plates, when 1 volt of force is applied.

1 farad = 1 coulomb / 1 volt

1 coulomb represents ~ 6 x 1019 electrons

Common Structure


fCXZ C 2

1

“Pure” Capacitor

Where:f is frequency (Hertz)C is capacitance (Farads)

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E-01 1.E+01 1.E+03 1.E+05 1.E+07

Imp

ed

an

ce (

Oh

ms)

Frequency (kHz)

Impedance vs. Freq. 47 µF Capacitance

C


Capacitor with Equivalent Series Resistance

C ESR

22 ESRXZ C

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Imp

ed

an

ce (

Oh

ms)

Frequency (kHz)

Impedance vs. Freq. 47 µF Capacitance 0.25 Ohms ESR

0.10 Ohms ESR

0.05 Ohms ESR

0.01 Ohms ESR

0.001 Ohms ESR


Capacitor with Equivalent Series Resistance and Inductance

1.E-03

1.E-02

1.E-01

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E+05

1.E-01 1.E+00 1.E+01 1.E+02 1.E+03 1.E+04 1.E+05 1.E+06 1.E+07 1.E+08

Imp

ed

an

ce (

Oh

ms)

Frequency (kHz)

Impedance vs. Freq. 47 µF Capacitance with 2.5 nH ESL

0.25 Ohms ESR

0.10 Ohms ESR

0.05 Ohms ESR

0.01 Ohms ESR

0.001 Ohms ESR

C ESR ESL

22ESRXXZ LC

fLX L 2Where: L is in Henries

self-resonant frequency.

LCf

2

1


Capacitor FundamentalsParasitics and Ripple Voltage


Capacitor Equivalent Circuit


Switch Closed

CurrentON

ChargeCapacitor Supply

LoadRequirements

LoadCurrent

ESRVC = VL(Closed) - VESR

Capacitor ChargeESR Impact


Switch Open

CurrentStopped

DischargeCapacitor Supply

LoadRequirements

LoadCurrent

ESR

VL(Open) = VC - VESR

VL(Open) = VL(Closed) – 2xVESR

Capacitor DischargeESR Impact


Ripple Voltage Effects

Ideal

MLCC (X5R)

Polymer

+ ESR

+ L

+ DC Bias

+ Cap Roll-Off


Capacitance: 200 µFESR: 33 mΩESL: 100 nH

20m

v

ESL Voltage Spikes

Capacitance InducedVoltage drop

ESR Voltage drop

Voltage recovery from Power Supply Unit (PSU)

Transient Response (C+ESR+ESL)


Capacitor FundamentalsRipple Current and ESR


Ripple Current Capability

• Ripple current refers to the AC portion of the current signal applied to a device.

• Heat is generated by ripple currents.

• Several factors contribute to the ripple capability of a capacitor:

– Dielectric material and associated DF

– Electrodes

– Frequency

– Package size (surface area)

– Package leads

– Allowable temperature rise

– Heat sink & cooling system


Ripple CurrentTemperature Rise


Ripple CurrentESR Changes with Temperature

Impedance and ESR – C1206C106K8RAC @ 25C with 0VDC Bias Impedance and ESR – C1206C106K8RAC @ 85C with 0VDC Bias


Ripple CurrentK-SIM Example: C1206C106K8RAC


Why ESR is ImportantPower Consumption (Heat)

Lower ESR Lower Power Losses Higher Efficiency


Why ESR is Important

• Why ESR is important:– Power Loss = 𝐼 ∗ 𝐼 ∗ 𝐸𝑆𝑅

– Simplified to 𝐼 below (loss is a little higher with 𝐼 )

𝑃 = 1A x 1A x 0.010Ω = 10mW (using 1A average current)𝑃 = 5A x 5A x 0.010Ω = 250mW (using 5A average current)

Lower ESR Lower Power Losses Higher Efficiency


ESR Comparisons Across Dielectrics

Dielectric Min. ESR [Ohms]

Aluminum Polymer 0.003

Ceramic 0.004

Tantalum Polymer 0.005

Aluminum Electrolytic 0.005

Tantalum MnO2 0.01

Film 0.01


Thank You!

wilmer companioni - kemet webinar -- capacitor application ......microsoft powerpoint - wilmer...

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