Electronics > Projects, Designs, and Technical Stuff
My constant current load - 90W , 3A 30V
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Spikee:
Most of the code is uploaded now. I still have to connect the mosfets together and screw the resistor on the heatsink

Pics:
Hello world :
https://www.dropbox.com/s/i4czyuqh3wfhxnm/2012-12-05%2022.08.35.jpg

Mosfets on heatsink:
https://www.dropbox.com/s/xdn9em9bar9b0d5/2012-12-05%2022.09.21.jpg

Mounting of mosfet:
heatsink -> thermal grease -> mica plate -> thermal grease -> mosfet
robrenz:

--- Quote from: blackdog on December 05, 2012, 08:30:04 pm ---0.1 Ohm wire resistor... Mmmm

~ 9cm, copper wire, 0.1mm diameter.

Try it,

--- End quote ---

That's called a fuse  ;D
Spikee:
It is all hooked up now =) .
i made a small mistake at the dac (upside down) and after i put it correctly it  shorted somehow after a while.
Since it is verry late and i should go to bed i just put it in pwm mode and play whit it.
I got it around 80-90W and you could feel the mosfets get hot after a few minutes (not to hot .. just hot :P )
the heatsink temp was climbing resonably fast (fan still on 5v , other people are sleeping) but did not get over 40 deg.c for the time i tested it.

I need to order a new dac and that will take a few days, until then i can just play in pwm mode.

gr spikee
LEECH666:

--- Quote from: blackdog on December 05, 2012, 07:19:02 pm ---Hi Spikee,

For the best sharing of the currents give eacht Fet a small Source resistor (0.1 Ohm)
And, don't forget to place the Fets on the good site of the heatsink!

This is the way to do it...


Kind regarts,
Blackdog

--- End quote ---

Hi blackdog,

what's the purpose of C1 in this circuit?

Sorry I don't want to high jack this thread, but I am working on my noob attempt of a higher powered dummy load in this thread. Should I add this capacitor in my circuit?
blackdog:
Hi Leech666

It's for stability, its best mounted close to the Fet end the lower site of the 0.1 resistor.
You can keep it as small as posible if you modulate the current source with relativ high frequenties and low current's.
In every design you make you have to check the values, is my design stable?
In almost every schematic on the Internet I see no or not enough decoupling.
Decoupeling is very important!!!

Some info over decoupling and why
TI
www.ti.com/lit/an/sloa069/sloa069.pdf

Analog Devices
www.bramcam.nl/MT-101.pdf



Kind regarts,
Blackdog
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