Full Build Analogue DC Load

In previous videos we looked at how to build an analogue electronic DC load and also a few different displays that could help with seeing what’s going on
So it has finally come to fruition and I am pleased to show the first build from what we have learned
This unit will handle plenty of load, I have already left it for several hours with 30V and 1.5Amps so 45 Watts, and it was barely above ambient and have also loaded with 60V at 1.5Amps with no ill effects so I have confidence it will perform for most of my desired uses
The display provides 4 digits of remarkably accurate readings for voltage and current and the unit will also handle input from an Arbitrary Waveform Generator (0-5V representing 0-5A) and up to about a 2 - 3 KHz square wave if you so desire.
I will be following up in the near future with a microcontroller based version but for now I at least have a good tool for the LAB that will be very handy for testing power supplies and batteries as well as a few other options I’m sure
Schematics etc. will be posted soon so you can build your own or you can refer to previous videos for more details
The only thing lacking right now is a fan control so slow it down when not running with a big load, this would be nice from a noise perspective but not essential

[@elboa8]

One to build, for sure. Thanks Peter.

[@mortenrolsing7137]

Realy love your videos, Thanks. I am realy learning a lot. Greatings from Denmark

[@TheBreadboardca]

Here is a post on Element 14 where I have the schematic posted and the STL files for the front panel I created www.element14.com/community/groups/test-and-measurement/blog/2015/07/31/complete-analogue-dc-load-0-5a-0--60v-but-not-300w

[@necbd8893]

Great job 👏

[@milanmladenovic]

Great video. Thanks

[@hankus253]

Wish some of the items you were pointing out were in view of the camera.

[@gnomishworks]

Great job on the DC load. A bit long a parts, but well done. Question on the voltage reference. Would it help the Mosfet drive if you used a 10v reference instead of 5v and amplified the arbitrary waveform input by 2. It seems everything else is 10v capable. I have a couple of LT1236AIS8-10 references and wondered if that would work/help. Thanks

[@TheBreadboardca]

It is all 10V compatible so it would not harm. and yes, if you up the reference to 10V you will need to either adjust the ARB input to match or divide it a little differently to compensate. either way will work

[@thecombatengineer7069]

DC load BOM : $50, Agilent 33622A $3900. For just $3950 you could have your own!

[@TheBreadboardca]

Actually the 33622A is about 8000CDN ++ as it also has all the options, Memory, GPIB, BenchVue etc. But more seriously, if I had a really low cost wave gen with as good a rise time at the time I would have used it as the source, the point there was to have an excelent input rise time in order to minimize its effect from the final measured rise times. When your measuring or characterizing something you should try to have measurements and source signals at least 10 times the resolution, im pretty sure I exceeded that lol.

[@jurgenollig6196]

Many thanks also for that, I am learning a lot too.

[@felixcat4346]

Nice vid, but it would have been better to not compartmentalize the theory using the function gen utilization and the trimmer pot. Not obvious to the uninitiated what the benefit of introduction of wave forms in a device like a dummy load is useful for.

[@suzaneouroumis8150]

Hi Peter, I believe there is a weak link in the DC load circuit. I build one and it was working fine. For some unknown reason the DC load mosfet shorted inside - while checking the mosfet offline - i found its showing continuity between drain and source. After replacing the mosfet the DC load was not working- i found the opamp is heating - replaced opamp and its working now. Do you think the gate should be driven through an optocoupler ?

[@TheBreadboardca]

It should not be necessary, I have seen many similar designs and they all drive the FET directly., an opto would only be needed if there is a significant difference between the source voltage and the op-amp output range that would take it out of its operating range or common mode voltage. I have used mine several times with no issues. If you have further information regarding the scenario that caused the failure i would love to hear it.

[@elboa8]

Final circuit please, Peter!

[@TheBreadboardca]

elboa8 www.element14.com/community/groups/test-and-measurement/blog/2015/07/31/complete-analogue-dc-load-0-5a-0--60v-but-not-300w

[@elboa8]

Peter Oakes Thanks...