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Pulse Test of Firing Capacitor Characteristics
NDIA Fuze Conference Baltimore, MD 7-9 July 2015
7 July 2015 1
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Insight
7 July 2015 2
Generally I’m not known for being too bright,
But, a Google search can make you an instant genius !
=
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Source of Technique
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High Frequency Measurements Web Page Douglas C. Smith URL: www.dsmith.org
A Web search turned up a “Technical TidBit” on the referent web site “Measuring Capacitor Self-Inductance and ESR”
The purpose was to measure inductance and ESR with regards to the capacitors’ pulse performance as a bypass capacitor in a digital circuit or its ability to shunt current in an ESD role.
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New Application
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Most capacitor data is given at AC. Some data is DC but not pulse.
When we perform a ringdown test, We are looking for peak amperes, inductance, and resistance.
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Pulse Testing
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So, can we do pulse testing, and how does it relate to ringdown data?
Doug Smith Fixture
New Test Fixture
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Test Set-Up
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Pulse Generator 1 µsec pulse 2.5 volt amplitude 50 Ω source
Oscilloscope 100 MHz or Better 5 mv / div, 10 nS / div-typical Dependant on inductance, etc.
Use 50 ohm coax cables with BNC connectors, ~ 2 Ft and equal lengths.
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What Do We See?
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Typical Capacitor Charge Waveform
If we zoom in, this is what we see !
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What Does That Waveform Represent?
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Parasitic Inductance of Capacitor,
ESR of Capacitor,
Since we use a 2.5 volt pulse into a 50 ohm resistor, current, I (di) is 50 mA
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Testing
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Like a Kid with a new toy, I started testing all kinds of stuff!
Capacitors NovaCap Wright Poly Film High voltage ceramic Regular chip ceramic
CVRs Barrel Clamp (Stripline)
Inductors
But, not the cat
Resistors
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General Parts
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Surface Mount Resistor, .10 Ohms Measured L=2.2 nH, R=100.73 mΩ
Molded RF Inductor 220 nH Measured 186 nH
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Firing Capacitors
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Pulse Test Ring Down
NovaCap 3640R144K152P IPEAK 2544 A
L= 1.530 nH L= 13.72 nH
R= 126 mΩ R= 42.31 mΩ
Wright SMN6964TR IPEAK 2035 A
L= 4.115 nH L= 16.49 nH
R= 213 mΩ R= 65.74 mΩ
Vishay PolyFilm ? IPEAK 1487 A
L= 13.65 nH L= 35.52 nH
R= 237 mΩ R= 65.74 mΩ
Summary of Pulse Test vs. Ring Down in Freddie Fireset
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Barrel CVR Measurement
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Pulse Measurement Data: L=9.259 nH, R=15.9 mΩ
CVR Resistance is .005087 Ω, At 50 mA, E≈ 258 µV. Not likely to measure that on my scope! But, it could also imply 10 mΩ of Fixture Resistance.
Clamp CVR is ~ 2 nH less
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A Potential Firing Cap ?
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High Voltage X7R Dielectric, 500 – 3,000 VDC (Commercial & Automotive Grade)
Kemet C2225C104KFRACTU 0.1 µF, 1.5 KV
Pulse Data: L=1.49 nH, 130 mΩ So I put two in parallel, must be twice as good, right?
2 in Parallel, Pulse Data: L=1.02 nH, 94 mΩ Well, not quite!
Have not performed ring down yet. Most all data sheets say X7R material not suitable for pulse applications. Need to run that to ground.
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Summary
The test method may have value in testing potential capacitors and measuring other components
There appears to be a correlation between pulse inductance and performance
There is a weak correlation between pulse ESR and performance
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Questions?
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Fred E. Piering Weacomm, Inc. 2585 Tuscaloosa Trl Maitland, FL 32751-5149 [email protected] Office: 407-645-1688 Cell: 321-356-0239