Looking for good simple DIY project of Electronic Load  - Page 1
Forum section: electronics / projects

author: 001
author_rank: Super Contributor
timestamp: November 07, 2018, 05:12:17 pm
content: Hi!I`m Looking for good (i.e. stable and rugged) simple (since I`m 60 years old tech, not an engineer) DIY project of Electronic LoadNo mc`s, only discrete transistors and some opams -- I hope to build it from my basement scrapit would be nice that I could modify the circuit for different voltages and currentsCan You recommend one please?

author: ogden
author_rank: Super Contributor
timestamp: November 07, 2018, 06:35:28 pm
content: This project looks good, seems to match your requirements:https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/

author: dardosordi
author_rank: Regular Contributor
timestamp: November 08, 2018, 02:27:34 am
content: Jay’s load (link in previous message) fits the description perfectly. I’ve built one and I’m pretty happy with it.

author: MarkF
author_rank: Super Contributor
timestamp: November 08, 2018, 02:56:35 am
content: The thing I don't like about Jay's Dynamic Load is that you need a dual power supply. I built something similar to Dave's Dummy Loadand Peter Oakes Loadthat only requires a single +12V supply. I set my max current at 1.5A but with a change in the sense resistor to 0.1 ohm and a very large heat sink and fan you could go to 5A.This is what I did:

author: 001
author_rank: Super Contributor
timestamp: November 08, 2018, 12:10:10 pm
content: Thank You!But IXYS are WERY expencive units!I have no one in my basement junkCan I use some common MOSFETs?

author: MarkF
author_rank: Super Contributor
timestamp: November 08, 2018, 01:00:52 pm
content: What current range are you looking for?Or, what MOSFETs do you have?The IRFP064 MOSFET I used is only $2.59 USD atMouser.

author: aheid
author_rank: Regular Contributor
timestamp: November 08, 2018, 01:46:12 pm
content: Quote from: 001 on November 08, 2018, 12:10:10 pmIt's my understanding you'll want to avoid trench-style MOSFETs, and rather go for planar MOSFETs.Here's a couple of references I foundhttp://www.eeherald.com/section/design-guide/mosfet_new_trench.htmlQuoteQuoteAndhttps://www.powerelectronics.com/discrete-power-semis/are-trench-fets-too-fragile-linear-applicationsQuote

author: perieanuo
author_rank: Frequent Contributor
timestamp: November 08, 2018, 05:01:58 pm
content: I built one with one zener, one opamp LM358 and 4 mosfets, works great up to 5A without too much heating (well I put one cooler from an older processor), tooked 30 mins to assemble, works great.only the multiturn is maybe a issue, you can put thoe a normal potentiometer.if you can't find the schematic on google,whistle I'll post it myselfI think I can go up to 20 amps with the thingEnvoyé de mon iPad en utilisant Tapatalk

author: 001
author_rank: Super Contributor
timestamp: November 08, 2018, 05:05:31 pm
content: The main problem is MOSFET SOAso I need only 0.2-0.4A but 400VCan I use some oldy but goldy BJTs like BU508A?

author: aheid
author_rank: Regular Contributor
timestamp: November 08, 2018, 07:26:30 pm
content: Quote from: 001 on November 08, 2018, 05:05:31 pmYou say "only", but 0.4A * 400V = 160W that the load needs to dissipate, that's not "only"...Looking at the BU508A datasheet, at 400V the SOA rates it at about 0.0175A max, or 7W. So doable if you have about 30-40 of them in parallel.Going by the datasheet something likeFGH40N60SMDFshould do it, assuming you're able to keep the case at 25C, but I'm no expert so.

author: 001
author_rank: Super Contributor
timestamp: November 10, 2018, 02:27:01 pm
content: Quote from: aheid on November 08, 2018, 07:26:30 pmYeaI can use oldstyle welding gear for parts

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: November 12, 2018, 12:42:18 am
content: Hi,Making a high voltage load has its challenges, because of the Safe Operating Area, SOA, of the MOSFETs in the linear region.Bipolar transistors do not solve the problem. BJTs suffer from something called second breakdown, if operated at high voltage and low current.Here is a concept for putting MOSFETs in series to make a high voltage load. I would use IRFP450 transistors in this circuit. I didn't have a SPICE model handy.I have put three MOSFETs in series in each position. This technique can be used for any number greater than 2.The main downsides to this technique:1) The minimum input voltage to the load is increased by one gate threshold voltage for each MOSFET. As shown the minimum input voltage is about 10V.2) The MOSFETs have to insulated from the heatsink.The upside:1) It really helps with the SOA problem.I would keep each MOSFET dissipation to be under 40W.In the example shown I have 6 MOSFETs so 240W with suitable (very large) heatsinks.I have attached the LTspice model.Regards,Jay_Diddy_B

author: 001
author_rank: Super Contributor
timestamp: November 12, 2018, 07:22:10 am
content: Quote from: Jay_Diddy_B on November 12, 2018, 12:42:18 amawesome idea!thank You! best regards