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Blog LabView process to measure DC:DC converter efficiency
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EMI-Reduction-Techniques
Engagement
  • Author Author: Jan Cumps
  • Date Created: 4 Jan 2025 11:49 PM Date Created
  • Views 1733 views
  • Likes 10 likes
  • Comments 8 comments
  • RoadTest
  • dc-dc
  • vishay
  • 2000-scan
  • dmm6500
  • smps
  • keithley
  • labview
Related
Recommended

LabView process to measure DC:DC converter efficiency

Jan Cumps
Jan Cumps
4 Jan 2025

I'm evaluating a Vishay microBRICK switch mode converter. The converter is Vishay's  Reference Design for a 4.5 V to 60 V Input, 6 A, DC/DC Synchronous Buck Module SIC967 . One of my lab tests is to validate efficiency specs. In this post, a LabView flow is going to replicate a characteristic chart from the datasheet.

image

Efficiency test

The SIC967 datasheet has a particular chart that's easy to replicate with the evaluation board: Efficiency vs. Output Current, with VOUT = 5 V, fsw = 500 kHz.

image

The chart shows the efficiency curve for output current between 0 and 6 A, for 4 different input voltages. This is one of the available setups of the kit. 

image

Bench setup

I'm using 3 instruments for this exercise. ALl are LabView capable:

  • PSU: Rigol DP832A, with channel 1 and 2 in series
    • Deliver Vin (12 - 24 - 36 - 48 V)
    • Measure input current
  • eLoad: my own
    • draw current from the DUT, between 0.1 and 6 A
  • Bench meter: Keithley DMM6500 with 2000-SCAN card (6 inputs used)
    • 1: internal DMM temperature for cold junction compensation of channel 2
    • 2: thermocouple attached to SIC967
    • 3: Iout - measures the voltage drop over the kelvin terminals of the eLoad's shunt resistor
    • 4: Vin at the DUT's probe points
    • 5: Vout at the DUT's probe points
    • 6: Vpowergood at the DUT's probe points

image

LabView

image

  1. PSU settings
  2. eLoad settings
  3. execution progress
  4. bench meter results

Setup

Initially, the flow connects to the 3 instruments and sets them up:

PSU:

Set Channel 1 and 2 to 0V, set current and Over Voltage limits, and set them as tracking, This will take care that when the flow changes the voltage of Channel 1, channel 2 follows along.
I've done that because 1 and 2 are in series to be able to deliver 48 V. The channels are switched on.

eLoad:

I'm using the low level direct DAC write API of the load. The load is set to draw 0 A, and activated.

Bench meter:

The first 6 channels of the scanner card are configured:

  1. Temperature, RTC, Pt100: measures the point where the thermocouple is connected to the card - the cold junction
  2. Temperature, Thermocouple, K-type: measures the switch IC case temperature
  3. Volt, 1 V dc: measures the shunt resistor of the eLoad. We 'll divide this value by 0.05 Ohm to get output current.
  4. Volt, 100 V dc: measures the input voltage at point of load
  5. Volt, 10 V dc: measures the output voltage at point of load
  6. Volt, 10 V dc: measures the power good signal

Flow

  • Loop through the input voltage, from 12 to 48 volt. In 12 V increments
    • Loop through the output currents, from 100 mA to 6A, in 55 steps
      • get input current from the PSU
      • get the 6 measurements from the bench meter
      • write data points to an excel file

It's a big flow. Here's the little excerpt where the bench meter samples the 6 channels, all at once:

image

The complete project is attached to this post.

Results

Spreadsheet: Column A - > N are generated by the LabView flow. O -> R are calculations based on them. S -> V are the results put in a matrix for the chart below.
I made the Rshunt value configurable. Although it's close to 0.05R, it drifts a little based on its temperature. And the impact on efficiency accuracy is significant.

The spreadsheet is attached.

image

Graph: compare it with the graph from the datasheet at the beginning of this post

 image

Thank you for reading

measureefficiency_35.zip

labview.zip

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Top Comments

  • Jan Cumps
    Jan Cumps 7 months ago in reply to JWx +1
    Except for the Rigol oscilloscope, all instruments that I used have USB that does not share ground with the measurement leads / probes. I relied on that. I didn't use an isolator, just one of those very…
  • Jan Cumps
    Jan Cumps 7 months ago in reply to JWx +1
    additional warning: I used an extension card in my bench meter. It turns it from 1 channel into 10 channels. These are all 10 isolated from each other . 2 relays per channel take care that one channel…
  • Jan Cumps
    Jan Cumps 7 months ago in reply to JWx

    additional warning: I used an extension card in my bench meter. It turns it from 1 channel into 10 channels. These are all 10 isolated from each other .

    2 relays per channel take care that one channel is fully wired out before another channel is wired in.

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  • Jan Cumps
    Jan Cumps 7 months ago in reply to JWx

    Except for the Rigol oscilloscope, all instruments that I used have USB that does not share ground with the measurement leads / probes. I relied on that. 

    I didn't use an isolator, just one of those very cheap USB extenders, to get enough ports for the meeasurements.

    I did not use the oscilloscope in the automated test setup, just connected it when I wanted to collect some screen captures.

    I ran the test setup isolated from ground. My power supply has the option to either work isolated or grounded.

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  • JWx
    JWx 7 months ago

    Nice setup! I am thinking about building something like this (using GNU Octave as a controller)... I have a question - is it safe to assume that USB connectors of the hardware are isolated, or better to use USB isolated bridges (for example ADUM3160 based) when connecting them to the computer?

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  • DAB
    DAB 7 months ago

    Great post Jan.

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  • wolfgangfriedrich
    wolfgangfriedrich 7 months ago

    Thanks for doing the light load tests as well. Those values are often overlooked for systems that have sleep mode and performance is worse than expected when not changing modes.

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