Electronic DC Load - Design and Build to test PSU Project

RE: Electronic DC Load - Design and Build to test PSU Project

alanthom — Mon, 28 Jan 2019 07:57:06 GMT

Dear Peter

I know enough to be dangerous [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-2564479c-fee6-492c-97d0-3633459da592/3872.contentimage_5F00_1.png:16:16]

Could you pse help. I built your cct and had much fun. I built the prototype on vero board and had one error. Corrected and things are looking good but!!! The MOSFET is driven on hard and no matter what I check, it short circuits the load. To try and assist, here are some measurements:

Measured at pin 2 on REF02 = 12,17v - correct, using a 12v reg.
Measured on pin 6 of REF02 = 5,47v - correct
Measured on pin 7 of op amp = max 5,47v and min 0,592v adjusting POT 2 (10k lin)
With switch selecting internal (not signal external signal), measuring pin 3 of op amp = max 3,27v min 0v
Measured on pin 1 of op amp, before 10k res = 18,3v
Measured after res 10k, driving MOSFET = 18,3v constant.... irrespective of POT 1 (10k lin) and POT 2

So the MOSFET is on hard IMHO. This is a mistake on my board but I just don't seem to be able to identify the error in wiring.

Any advice would be much appreciated.

BTW - any news re a printed cct board...I'm still trying to learn KiCad. A pdf of the track layout would help so much!

But I do not expect you to do my job for me [View:/resized-image/__size/16x16/__key/commentfiles/f7d226abd59f475c9d224a79e3f0ec07-2564479c-fee6-492c-97d0-3633459da592/3872.contentimage_5F00_1.png:16:16]

Warm Regards out of Africa

Alan

RE: Electronic DC Load - Design and Build to test PSU Project

stephanc — Wed, 28 Jun 2017 14:09:52 GMT

Dear Peter

How do one go about selecting the MOSFET.
I would have thought 5A 30V would be ample. The 70 Amps mosfet (IRFP064) has a very steep Id Vgs curve at low amps. Is this relevent?

I would have thought a requirement would be a 'Linear MOSFET'. What does it mean?

Would any of these be usable

1. IRL540N

2. IRF730B

3. CEP83A3

4. HRF3205

5. S20N60C3S

How would I parallel more that one to spread the heat better? Would you need some sort of balancing resister?

Why did you use a 50K for the current adjustment pod and not a 10K?

As you can see. I'm quite the novice!

Kind regards

Stephan

RE: Electronic DC Load - Design and Build to test PSU Project

Former Member — Sat, 30 Apr 2016 00:14:41 GMT

Thank you John

Sorry for my English

You know where I can buy the resistor R1

RE: Electronic DC Load - Design and Build to test PSU Project

Robert Peter Oakes — Fri, 29 Apr 2016 05:39:09 GMT

Hi All, I am also now in the process of gearing up to continue the project, I will start by providing a review and then proceed to automation, adding DAC control and ADC feedback to various controllers like Arduino, LaunchPads and Raspberry PIs. I will include parts list this time arround as well to help out sourcing parts.

But as John stated, my aim is to teach you what you need to design and build your own and as such am happy to answer any questions to help clarify the design I have presented

RE: Electronic DC Load - Design and Build to test PSU Project

Former Member — Fri, 29 Apr 2016 04:53:57 GMT

Maybe it would be good to put a parts list

RE: Electronic DC Load - Design and Build to test PSU Project

Former Member — Fri, 29 Apr 2016 04:29:53 GMT

The other question is that resistance put to increase the amperage

RE: Electronic DC Load - Design and Build to test PSU Project

Former Member — Thu, 28 Apr 2016 21:02:02 GMT

Hi, this excelent

But I have a problem

where not get resistance R1

Someone can tell me where to buy it? R1

RE: Electronic DC Load - Design and Build to test PSU Project

DAB — Tue, 02 Jun 2015 18:43:00 GMT

Great post Peter,

Have you considered do a PC board and providing a parts list for others to make your design?

DAB

RE: Electronic DC Load - Design and Build to test PSU Project

michaelkellett — Tue, 02 Jun 2015 08:45:06 GMT

@Peter, I may have missed it somewhere but I'm not sure what transient response you are aiming for with your power supply. Decent commercial supplies offer 50uS transient response times (I checked Keysight and Rigol) - so if your load is to be able to test to this sort of spec you need a 5uS response time - I can't quite understand why you are aiming as low as " only a few hundred Hertz".

If you reduce R6, possibly use a faster op amp and tune the compensation capacitor I can't see why you shouldn't get a much better response.

For transient tests I'm more likely to use a power resistor switched by a MOSFET which is either on or off - less flexible but (almost) 100% stable !

For steady state stuff I have an computer controlled electronic load but it was a lot pricier than your home brew.

RE: Electronic DC Load - Design and Build to test PSU Project

jw0752 — Tue, 02 Jun 2015 05:30:28 GMT

This looks like a great project. I need one of these more than I need another power supply. I will follow your project with interest.

John