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Cheap DC-DC and AC-DC Converters Automated Efficiency Measurement Method

Well, the thing is – now you can easily buy DC-DC converter chips for less than $0.2 in relatively small quantities. And because of that, and because different voltages required by microcontrollers and other chips – you can find yourself putting two or even more DC-DC converters on a single board.

Designing a DC to DC converter is a bit more problematic than using linear regulator. And one of the things you need to do – is to graph its efficiency vs. output current, or input voltage, etc.
So in the end you could get graphs like these:

That’s a pretty flat response and high efficiency – but that’s not always like that.

Usually this kind of things is done using programmable power supply in conjunction with programmable electronic load and some software, like LabView or even simple Python scripts + some spreadsheet software.

When you don’t have programmable power supply and/or programmable electronic load – then you have to do this manually with four multimeters, spreadsheet software and maybe a piece of paper.

Unfortunately it takes hell of a lot more time than with using previous method… but at least it’s as cheap as it gets :)
And if you need to do this every time when you changing some aspect of you converter, like inductor, for example – then you wasting lots of time, plus you’ll be bored to death pretty soon.

The method

Well, my idea itself is nothing new, in fact I wouldn’t be surprised if someone have already made something to solve this problem (I haven’t done much research on this topic)

So the idea is to connect those four multimeters to your computer and write specialized software which would help to effortlessly make those efficiency graphs of DC-DC or/and AC-DC converters.

The pros of this method are:

  • The chances are that you already have four multimeters that can be connected to PC
  • You can use a simple adjustable power supply and electronic load, and manually set input voltage and output current load
  • This is much cheaper than buying a proper programmable PSU and programmable electronic load, because to buy PSU and EL with somewhat accurate readings and good resolution you need to spend more than $1k on each – those cheap chinese PSUs and ELs are just piece of crap when it comes to readings accuracy
  • You can easily test both DC-DC and AC-DC converters, and you don’t have to buy separate high voltage programmable PSU to do so
  • Did I say it’s cheap? Four cheap multimeters with decent accuracy, resolution and PC connectivity would cost you next to nothing. For example UNI-T UT61E 22000 counts DMM with DC accuracy (+/-)0.1%+2 counts cost only $65. Of course that accuracy would be much lower in time, but still!
  • You can combine any four multimeters you have, that can be connected to PC
  • It is possible to use cheap programmable electronic loads and power supplies in conjuction with multimeters to do fully automated testing with good accuracy
  • It’s much much faster than doing this by hand

Cons:

  • In case of using ordinary PSU and EL you still need to do something by hand, like adjusting input voltage and load current
  • It is somewhat slower with cheap multimeters than with using proper PSU and EL, but for that price – who cares?
  • Also, if not using triggers you might need to click a button each time you adjust input voltage or load current to take measurements (but it’s just one click – not manually typing readings from each of four multimeters to spreadsheet)
  • Someone has to write this software..

Unfortunately right now I don’t have much time to sit and write this piece of software. I was going to write it from scratch using C++ and QT – so it can run on Windows, Linux and Mac. Plus I wanted it to be open source. But since right now I’ve got lots of things to do, I’ve decided to just write this small article, so maybe someone would want to do this.

But! There’s already big part of the job is done. Guys from http://sigrok.org have already done interfacing with different multimeters and other measurement equipment. It’s an actively developing project, that needs more contributors, so visit http://sigrok.org – they need your help to put more devices to the “supported devices” list.

So having drivers for various multimeters in place, there only left to write a software that can take that output, do some calculations and make a graph(s).

And I understand, that it’s not that easy to do that, in fact many and many hours needed to develop a GUI, make internal logic and don’t forget about usability. But as I said, if I can’t do it right now, I don’t want to keep this idea(if you can call it that) to myself. Maybe it’ll eventually help someone… who knows?

2 comments

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  1. paul says:

    for $0.2 no wonder you have null eficiency at low voltages.can u post a schematics,too (actually i need one bluetooth bcd-210)

    1. admin says:

      lamest comment in a long time :)
      there’s 4 things you wrong about:
      1. Efficiency is not null, it drops to 72% and 75% respectively.
      2. Not low voltages, but low load currents.
      3. Graphs are from ~$5 or so, converter from Linear Technology, and definitely not for $0.2 converter.
      4. $0.2 converter chip, I was talking about is MC34063 – which could be pretty efficient – depends on how you use it.

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