How To Breadboard An Electronic Load Design For Testing - Page 1
Forum section: electronics / beginners

author: t1d
author_rank: Super Contributor
timestamp: September 11, 2018, 04:05:25 am
content: IIRC, breadboards can add capacitance. Op amps are prone to oscillations. So, is it even possible to correctly test an e-load, on a breadboard?Additionally, there is the issue of heat. Mount the MOSFETs, off of the Bbd, I would think. The current sink resistor might get hot, too.What would be safe working volts and amps? The control circuit is +9v to -9v.I am working on Jay's design.https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/My proposed schematic is attached.

author: JS
author_rank: Frequent Contributor
timestamp: September 11, 2018, 05:46:50 am
content: Well, for high currents, as high current path is usually pretty simple I like to run it outside the breadboard with alligator clips to the power package pins or solder some wires, or just build a small perfboard with some current reinforcement of the power stage. I just measured contact resistance to be about 50mΩ, so for a 5A load you will see about a watt in the contact which seems that it might get warm to me.For low speed circuits capacitance isn't usually that problematic, I've just measured about 40pF for the long power strips, so from there I'd guess a few pF between adjacent lines. That will be in the order of parasitics you are likely to see in a PCB so not much to worry about. Of course breadboard isn't a place for RF stuff but for a DC load control circuit it's just fine.About the voltage, 18V is nothing, you are safe there, I'd be comfortable with 50V as well, I have pushed things making a mains dimmer on a breadboard and I'm alive, 220V here so it can withstand 310V peaks between adjacent rows, I'm not saying you should do that but I can tell the story.Once designs get messier I prefer to etch a PCB and test things there, put as many dummy components as I think it might need, any non populated components doesn't make a difference and any dummy series component needs a jumper but that's not the end of the world. I can make a PCB in very little time and I hold the flag for self etchers even with all PCB manufacturers out there making dirt cheap PCBs, but they take a few weeks to get to me, I can redraw a PCB, make it and have it populated in just a few hours!JS

author: t1d
author_rank: Super Contributor
timestamp: September 12, 2018, 12:00:51 am
content: JS, this is really good information; thank you. I feel much more confident, in moving forward to Bbd the circuit. Breadboarding will allow me to try different designs.

author: joeyjoejoe
author_rank: Frequent Contributor
timestamp: September 12, 2018, 10:03:28 pm
content: I'm working through a similar challenge on a breadboard currently and I'm finding voltage drop is a bit annoying when trying to detect current. Have to make sure the current stays "outside" the breadboard traces.

author: Sceadwian
author_rank: Unknown
timestamp: September 12, 2018, 10:54:03 pm
content: That's likely contact resistance. The traces themselves can actually handle modest current but every one of those little jumpers is another contact resistance point.Quote from: joeyjoejoe on September 12, 2018, 10:03:28 pm