Electronics > Projects, Designs, and Technical Stuff

My constant current load - 90W , 3A 30V

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Harvs:
But they don't meet your voltage requirement  :-//

Anyway you've bought them now, so just make sure you don't exceed that 55Vds.

I would still use separate control loops and forget about matching FETs.  But that's you're choice, and I guess you've already got that board made and the single high powered resistor.

BTW, I only talked about the IXFK230N20T because it was the cheapest FET that met your package requirements.  By no means was that a one off case, it's just the cheapest I could find.

Spikee:
@ Harvs :

Sorry for the confusion :P my specs are very loose ... i just made up some specs .
I was very buzy whit a college project all week but today i had time to lasercut the front panel @ the FabLab in my school.

(still have to sand of the exessive black marker ink. I should have selected higher power to engrave the text so it would be black but ... beginner fault  :-//  )

Pic:


I still need to laser out some holes and make some extra markings , but it is a start.


I have learned that seperate control loops and seperate load resistors is the way to go but i now have this pcb and i would like to use it.

Spikee:

--- Quote from: blackdog on November 29, 2012, 11:21:14 am ---Hi Spikee

Buy 5 a 10 of these Fets:
http://www.dickbest.nl/index.php?_a=viewProd&productId=2164

Select the fet's, see picture


Kind regarts,
Blackdog

--- End quote ---

The results: (had to put a few 1k pots in series to get 1A accuratly ...)

https://dl.dropbox.com/u/100819959/mosfet%20scatter.pdf

It won't be super accurate because the current would shift about. But i measured as good as i could.

Fet 2 and 4 would be the best match.  I will test the rest of my circuit in a few hours.

gr. spikee

blackdog:
Hi Spikee,

Fets 2 and 4 looks good :-)

I know its a little drifty, thats wy i told you to mount the Fet on a heatsink.
If i told you use 30V and 1.5A... No way, drift all over the place.
You dit a fine job.

Please let me see your final schematic.

Kind regarts,
Blackdog

Spikee:
i mounted it on the heatsink but they were still a bit drifting . The fan wasn't hooked up so i did a second test whit short on time and let the heatsink cool to the same temp. I got the same results =) . I just mounted the two fets and need to find a good spot to mount the resistor.
I'm drawing a simple schematic for you.

Output schematic:
the gate resistor is mounted directly on the gate pin of the mosfet.


Thanks spikee

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