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CogniPower has developed an improved way to monitor current in the high-speed, high-current environment that is found in switched-mode power converters.
Accurate Current Measurement From DC To 10 MHz at 50 Amps
Our patent-pending current probe was created to address limitations of conventional techniques when monitoring AC and DC currents in switched-mode power converters. The combined needs for DC accuracy, high bandwidth, excellent common mode rejection, and low cost could not be met without new developments. Our probes use an ultra-low inductance sense resistor in conjunction with a novel sampling bridge to extend excellent common rejection to higher frequencies.
No Derating is Needed
Unlike clamp-on probes, no derating is needed. Below is a derating curve for an expensive, clamp-on current probe:
The graph is for a probe rated at 150 amps and 10 MHz – but not both at once. The maximum sustained current that can be measured at 10 MHz is 10 amps. Further, the insertion loss at 10 MHz is 0.1 ohms. That amounts to a major inefficiency at the higher currents.
Low Insertion Loss
Insertion loss from existing probes changes the behavior of the device under test, thereby limiting the usefulness of clamp-on probes for higher-current, higher frequency measurements.
Our insertion losses can be 10 to 100 times lower than clamp-on probes.
Interchangeable Sense Resistors
CogniPower current probes accept interchangeable sense resistors. With the appropriate sense resistor, arbitrarily high currents can be measured at full bandwidth. Ask us about high voltage options.
Previous approaches using sense resistors and differential amplifiers suffer from common mode rejection limitations. Our new current probe can handle situations where both ends of the sense resistor swing rapidly between different voltages, such as in buck-boost configurations.
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Waveforms showing a fast 36 V common mode voltage swing (bottom trace) and the
amplified output signal (top trace). The input signal is a 100 kHz triangle
wave, 100 mV peak-to-peak, superimposed on the 36 V square wave.
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Another view of the waveforms from the previous image, with the timescale set to 10 ns/div. The
slew rate is over 15,000 V/μs (bottom trace).
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The negative common mode transition is similar to the positive edge, also seen at
10 ns/div.
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We measure the common mode rejection to be greater than 70 dB at 100 MHz.
Use with Any Oscilloscope
The CogniPower current probe is powered by a built-in, rechargeable battery, and will work with any make of oscilloscope. Because it is self-powered during use, no extra paths are created through the power supply wiring. The probe is designed to survive the expected occasional mishap.
Introductory Price: $995
The low introductory price reflects our intention to further integrate the current probe circuitry to reduce its cost and size to the point that current monitors built on these principles
can be economically built into individual switched-mode power converters. Think of the possibilities.
More pictures of the current probe
Download brochure (769 KB)
Download our 2009 APEC presentation (2.19 MB)
Download our 2010 APEC presentation (1.9 MB)
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