Looking for good simple DIY project of Electronic Load

[001]

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 Load
No mc`s, only discrete transistors and some opams -- I hope to build it from my basement scrap 

it would be nice that I could modify the circuit for different voltages and currents


Can You recommend one please?

[ogden]

This project looks good, seems to match your requirements:

https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/

[dardosordi]

Jay’s load (link in previous message) fits the description perfectly. I’ve built one and I’m pretty happy with it.

[MarkF]

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 Load



and Peter Oakes Load



that 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:

   

[001]

Thank You!

But   IXYS are WERY expencive units!  I have no one in my basement junk 
Can I use some common MOSFETs?

[MarkF]

What current range are you looking for?

Or, what MOSFETs do you have?

The IRFP064 MOSFET I used is only $2.59 USD at Mouser.

[aheid]

But   IXYS are WERY expencive units!  I have no one in my basement junk 
Can I use some common MOSFETs?

It's my understanding you'll want to avoid trench-style MOSFETs, and rather go for planar MOSFETs.

Here's a couple of references I found http://www.eeherald.com/section/design-guide/mosfet_new_trench.html

To have a clear estimation of the max power stress allowed on the device involved, we performed a test with the heat-sink out of the plenum and disabling the thermo resistor. The test was performed starting from low duty cycles continuously monitoring the plastic body temperatures. The device failed at 30% duty cycle after almost 25 minutes continuous working, joining in the plastic body case a temperature of 330°C. The result gives us an indication that the device has a high thermal stability before failing.

In the application STP141NF55 was replaced by a new trench device and the test results were vice versa negative. The device failed almost instantaneously when the duty cycle was switched on. This confirms that high current density technology makes a device weak in linear mode operation. In fact, linear mode working inside the device structure creates hot spots that probably exceed the 330°C, pushing the device itself in thermal runways.

And https://www.powerelectronics.com/discrete-power-semis/are-trench-fets-too-fragile-linear-applications

Beware of trench FETs operating in the linear mode. Published SOA data may not be adequate to determine safe use in your specific application. Also, published SOA data may be incorrect. Therefore, it's recommended that testing is performed using a representative thermal system and operating conditions beyond those required by the application.

[perieanuo]

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 myself
I think I can go up to 20 amps with the thing


Envoyé de mon iPad en utilisant Tapatalk

[001]

The main problem is MOSFET SOA
so I need only 0.2-0.4A but 400V

Can I use some oldy but goldy BJTs like BU508A?

[aheid]

The main problem is MOSFET SOA
so I need only 0.2-0.4A but 400V

Can I use some oldy but goldy BJTs like BU508A?

You 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 like FGH40N60SMDF should do it, assuming you're able to keep the case at 25C, but I'm no expert so.

[001]

The main problem is MOSFET SOA
so I need only 0.2-0.4A but 400V

Can I use some oldy but goldy BJTs like BU508A?

You 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.

Yea
I can use oldstyle welding gear for parts 

[Jay_Diddy_B]

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

[001]

awesome idea!

thank You! best regards