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For every magnetics component you design or specify, it is
immensely valuable to measure and archive the terminal impedance
characteristics at each step of your design, development,
and transition to manufacturing. This measurement is a sensitive
measure of how well the magnetics part is being built, and
can catch problems before they show up as failures on the
production line or in the field. This page describes how to
make these measurements.
More Application Notes
- Using the above setup, measure
the short-circuit
and open-circuit impedance of the power transformer from 10 Hz to 15 MHz. This
data should be collected for all magnetics that you build
or specify during the design and development phase of your
project. (Only one measurement for a power inductor). You
will use the data to help evaluate new manufacturers, and
as part of the comprehensive record of the magnetics' performance.
-
Make sure that
the short circuit you apply is of low
impedance, especially
for low-turn transformers. A terminating loop of just a
few cm diameter can result in an inductance measurement
significantly higher that the internal leakage of the transformer
you are trying to measure.
-
Measure dc
winding resistances with a four-terminal measurement setup. You can use a simple lab current
source and Fluke voltmeter to get very accurate dc measurements.
A similar setup with the AP 200 Parallel frequency response
analyzer will produce good results at frequencies up to
1 MHz or more for low resistances.
-
Leakage inductance
is a function of frequency. Make sure you specify the measurement frequency for both leakage inductance and magnetizing inductance
to your manufacturer.
-
For most switch-mode
power transformers, a sense resistor of either 0.1 or 1 ohm can be
used to extract the needed frequency response data.
-
With these
measurements, you will have data to calculate:
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Magnetizing
Inductance
-
Winding
Resistance(s)
-
Leakage
Inductance(s)
-
Open Circuit
Resonance and Q
-
Short Circuit
Resonance and Q
-
Winding
Capacitance (as low as 3 pF with the AP 200 Parallel
More Application Notes
Related page: High-Frequency
Magnetics Design Myths
© copyright
Ridley Engineering, Inc. 2007
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