Hi
Thank you all so much for the replies.Much appreciated!!!
@ Hero999 : current needs to be a square pulse.But your idea is interesting and I am thinking on how it could be improved to suit my needs..(i will explain my exact circuit requirement at the end)
@ ericgibbs : I will be more clear on my requirement.Since this is not an experiment,was just trying to put it in easy words
@ crutschow : The current will be slightly higher (with 1.25V drop).I am looking at LM338 on same principles after your suggestions,since the requirement is changed to variable current up to 5A.
@ KMoffet : Interesting !!!
I will explain exactly what I am intending to do.
The load under consideration is a kind of nichrome fuse,of which I have to test some parameters with my equipment.
Current should be variable from 1A to 5A in steps of 1A constant.
Voltage need not matter and I would be building a CV of 15V (I feel would be sufficient)
Now I have to program a one time pulse starting at 50ms up to 500ms in steps of 50ms.
After everything is set and I press 'FIRE' or something I will switch on a MOSFET to give a path to the current through the Load.
I am unable to understand a few things here though.
I primarily will set current with a fixed resistor bank and using a short circuit instead of load.
e.g. For 3A=15v/5E so would use a smaller R at say 4.5E to get a higher current. 15V/4.5E=3.33A (considering unknown load)
After this is set,I input value of pulse at say 50ms.
After this,I put the load on O/p and press 'FIRE'.
Now during this 50ms time I should limit the current w/o any overshoot at 3A by using some kind of variable resistor.
If the Load value is 5E then current will come down to 1.5A,which the circuit should compensate by either increasing the voltage or by a constant current source.
If I use a transistor as a variable resistor,wont the error correction take some finite time?which will not be permissible.
I hope I am clear enough..
Thanks and please get back with your valuable suggestions as always!!!