Electronics > Projects, Designs, and Technical Stuff
Another counstant current load for critics
001:
Hi
Is it good or bad project? :-//
https://diyodemag.com/projects/dummy_load
floobydust:
Bad.
Whales:
From the article:
(Viewing this image required javascript + a lightbox. :'( )
Whales:
Wait, they consider this a switching device? But this looks like a linear regulator.
Hmm, they have a scope shot of something that looks switching. There are no grid squares, so I can't tell what the 100mV scale means, but I suspect they have just zoomed into the ripple.
Also I am not sure you really need the 9V regulation stage. Ditch it and use your 12V directly unless your 12V source is unstable. I suspect it was born of them changing it from the "5V" design they mention.
Overall: it's a simple design built with jellybean parts. The IRF540 most people will use will be a greymarket fake (it works fine but won't meet datasheet specs, be wary of their remarks regarding the 175degC die limit). My only thought is to whether or not this device is stable and under what conditions.
Whales:
Some specific quotes about this design:
--- Quote ---Whilst this isn’t a perfect system, due to inefficiencies in both the MOSFET and the operational amplifier
--- End quote ---
"inefficiencies in the MOSFET" isn't the right wording or line of thought here. That's too easy to construe in many incorrect ways, this class of device always has the same "efficiency" regardless of the MOSFET used.
--- Quote ---the op-amp will attempt to rectify this difference by increasing the voltage at the output. This, in turn, saturates the gate of the MOSFET, which allows current to flow from the MOSFETs Drain to the source.
--- End quote ---
I would have thought this device operated the FET mostly in the linear region, not the saturation region.
I once bought or obtained an issue of Diyode after being recommended it. I didn't end up liking it, but I can't remember the full details.
It looks like they're focusing on the whole round trip of making a device from breadboard to box. That's nice. It's made from jellybean parts, it's performance won't be anything fancy, and there are a lot of tweaks I would do to the PCB for better perf; but I think that's outside their aims and misses the point. It's not intended to be an amazing spec dummy load, but instead shows you how you can start making your own (simpler) alternative to the off-the-shelf products the mention in the opening.
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