Interest in an arbitrary load - Page 1
Forum section: electronics / projects

author: sahko123
author_rank: Frequent Contributor
timestamp: July 16, 2020, 02:47:53 pm
content: I want to gauge the interest in designing an arbitrary load generator which can take an input from a waveform generator and turn it into a load at say 100mV per amp or 1v per amp of input. I'm also wondering olif anything like that alreasy exists and at what expense and maybe if there's enough interest it might be a fun thing to design. I know there are alot of active loads on rge forum but I've not yet seen one with a waveform input just dc loads.

author: magic
author_rank: Super Contributor
timestamp: July 16, 2020, 04:42:31 pm
content: Many of the existing ones could be made programmable by replacing a single potentiometer with a BNC jack, as they are basically opamp+transistor voltage followers which try to "mirror" the setpoint voltage on the shunt resistor. Maybe you would want some input protection, either to save the load from bad generator or to save the generator from catastrophic failure of the load. And there is the question of bandwidth...

author: sahko123
author_rank: Frequent Contributor
timestamp: July 16, 2020, 05:08:29 pm
content: Yeah mostly i think it would be for testing how power supplies would respond to ripple current so the higher the bandwidth the better.

author: MarkF
author_rank: Super Contributor
timestamp: July 16, 2020, 05:45:30 pm
content: You mean something like the eLoad I built?A 0-5V external signal provides a 0-2.5A load current.I forget now, but I believe the eLoad has a response up to 5KHz.

author: sahko123
author_rank: Frequent Contributor
timestamp: July 16, 2020, 06:37:30 pm
content: I guess so but 5khz isn't even halfway up the audio range

author: MarkF
author_rank: Super Contributor
timestamp: July 16, 2020, 07:44:53 pm
content: Quote from: sahko123 on July 16, 2020, 06:37:30 pmThinking about this a little more...A few months ago, I seem to remember this subject being discussed.Maybe hunt around. There a quite a few threads on eLoads here.

author: joeqsmith
author_rank: Super Contributor
timestamp: July 16, 2020, 11:00:02 pm
content: I made a switching one once.https://youtu.be/uRLLzFZlWrI

author: TheMG
author_rank: Frequent Contributor
timestamp: July 17, 2020, 12:32:04 am
content: Quote from: sahko123 on July 16, 2020, 06:37:30 pmFor the overwhelming majority of programmable load use cases, that is more than enough. Maybe there's some very niche application where that would be useful, but right now I can't think of one, what do you have in mind exactly???

author: sahko123
author_rank: Frequent Contributor
timestamp: July 17, 2020, 05:57:36 am
content: Audio power amplifiers because you want to get as high frequency a power supply load respouse as possible which often times doesn't really matter but in certain use cases where your using exceptionally low power transformers without leaving headroom for power. Like in a linear supply. That and it would still be interesting to try see how high frequency a response is possible and what limits it. Its essentially a way of testing a power supply that drives a high frrequency and high current load and not just on an off transient response but more complex things aswell or whatever the arbitrary function gen is capable of. My somewhat cheap and cheerful generator rigol dg812 can do the drive voltage of a car spark plug which means I could try make it capable of higher voltages like 200 or maybe 300v granted still nowhere as high a voltage as spark plugs but still.

author: MarkF
author_rank: Super Contributor
timestamp: July 17, 2020, 05:37:50 pm
content: I took a quick look at the Siglent SDL1020X-E DC Load for example.It has a CC Dynamic mode to 25 kHz.5KHz is pretty respectable considering it's only 1/10 the cost.The fly-in-the-ointment here is that the output of an audio amp is not DC.There is a negative voltage component not acceptable for the Load.

author: TheMG
author_rank: Frequent Contributor
timestamp: July 17, 2020, 06:33:14 pm
content: Quote from: sahko123 on July 17, 2020, 05:57:36 amThat would normally not be a concern, since the circuit design should make use of decoupling capacitors, so the power supply and/or regulator never "sees" those high frequencies.