electronic adjustable resistor

[luka]

Does any one have this kind of resistor?
For testing supplys,amps,...

 

[mrshow4u]

I'm not sure what you need. These might not deal with reverse polarities, ....I didn't check'm out. <http://www.home.agilent.com/cgi-bin...sg:pro&ID=1000001518:epsg:pro&COUNTRY_CODE=US>

 

[luka]

Yes like that, but I would like to build one myself,but I dont know where to start, and I don't have any schema for now.

 

[mrshow4u]

You could parallel up a bunch of MOSFET's and bias the gates up to make an adjustable power resistor. I've never tried that, but in concept it works. It sounds interesting

 

[luka]

That's what I thougt, but gate drive must be somewhat complicated, because it has to keep the resistance the same, independeble of voltage applyed to mosfer's.

 

[mrshow4u]

.. Yes, that's where the "fun" would come in. You'd have to monitor the summed currents, measure the voltage across the MOSFETS, then adjust the Vgs to mantain the load resistance.

 

[luka]

Now how to do that...

 

[luka]

It would be great to have adj. max current to.

 

[luka]

Uuu and max power limit.

http://www.elektor-electronics.co.uk/Default.aspx?tabid=28&art=50616

 

[jackinnj]

We have a great company in NJ -- Transistor Devices -- which makes electronic loads -- they have units which will dissipate 120kW !!! Very often you will see their units for sale on EBay or at Hamfests:

An externally hosted image should be here but it was not working when we last tested it.

 

[paulb]

We have a great company in NJ -- Transistor Devices -- which makes electronic loads -- they have units which will dissipate 120kW !!! Very often you will see their units for sale on EBay or at Hamfests:

Hey, I had one of their electronic loads. Took it apart for heatsinks, and the chassis become my P3A amp. It's in my living room.
I wonder if it worked? Never tried it. Got it for really cheap.

 

[powerbecker]

Yes like that, but I would like to build one myself,but I dont know where to start, and I don't have any schema for now.

Hello Luka,

this kind of circuit is fairly simple!
Much more simple is to "google" for it:
eg "electronic load" or "electronic load circuit"
(I try it!)

Regards
Heinz!

 

[gmphadte]

U need to construct an adjustable current sink.
Something like shown below

Gajanan Phadte

 

[Christer]

U need to construct an adjustable current sink.
Something like shown below

Gajanan Phadte

No, that's just an adjustable current sink. He wanted an adjustable resistance.

 

[gmphadte]

V remaining fixed, if u change the current, u are changing the resistance.
Just different names for the same thing

Gajanan Phadte

 

[Christer]

But I don't think V was assumed fixed. I think he really wanted a circuit that behaves as a resistance, but where you can set the resistance.

 

[gmphadte]

Such circuits and the commercial product shown can only test DC, such as DC power supplies, batteries etc. They are mostly employed for discharging batteries for testing purpose IMO.
For testing amps, no idea

Gajanan Phadte

 

[gmphadte]

May be he can make a motorised rheostst and control it electronically.

Gajanan Phadte

 

[luka]

powerbecker

I think simle enough will be this circuit.

Christer and gmphadte,

You are both right.
1.)It is for DC use
2.)But it can be used for low freq. ac, if you use rectifier

Read the article and you will know what I want.

I would like to get layout for PCB from one of you I any one has it.
If not I will just have to made it by myself.

What do you think?

 

[gmphadte]

Nice find.
Assemble it on a veroboard if u are in for a quick solution.
No Eagle with me.
If u don't have it, download it from cadsoft.de

Gajanan Phadte