Constant DC current source

[Affan]

I have been given a project to make a 2 ampere constant dc current source.
Can anyone explain to me the simplest method to do it? I have only 2 days, please help me!

 

[Nigel Goodwin]

You need to give more information, what is it feeding, and what supply does it need to be fed from.

 

[Affan]

The power suply might be a voltage source. Actually i dont know much about it. All i need is to make a circuit which outputs Constant 2A current.

 

[Nigel Goodwin]

There's not enough information there to make anything really, is this purely a homework question, and not a practical project?.

 

[Affan]

If anyone just asks you to build a 2A dc current source without any further details. What would you do and how would you do it sir?

 

[Affan]

It is a practical project. Ok please tell me what all information is necessary?

 

[JimB]

If anyone just asks you to build a 2A dc current source without any further details. What would you do and how would you do it sir?

I would then ask the following questions:

How accurate must the 2A be?
What supplies are available?
Do the supplies vary, and if so, by how much?
What load is it driving?
Does the load vary, and if so, by how much?
Are there any size or weight constraints?
Is it supposed to be portable?
When do you need it?
How much money have you got to pay for it?

JimB

 

[Nigel Goodwin]

It is a practical project. Ok please tell me what all information is necessary?

If it's a practical project then you must know what it's feeding?.

 

[Affan]

Sir this current source will be used to supply 2A constant dc current to variable loads. Portability isnt required. The current should be constant. Power supply can be of any suitable type.(Also tell me the most suitable power supply).(I am a first semester engineering student).

 

[Speakerguy]

Use an LM338K in a TO-3 package configured as a current source. It only requires one resistor in addition to the LM338K. You will need a power supply that can deliver two amps and a voltage that is 2.5V higher than whatever voltage might be developed on the output. It will need a large heatsink.

 

[Affan]

Please provide some further explanation and circuit diagram.(As i told i am a first semester student)

 

[Speakerguy]

Google "LM338K" and look at the data sheet.

http://users.pandora.be/davshomepage/current-source.htm

This is for the LM317. The LM338K basically works the same way, but it will do more current (the LM317 only does 1.5A).

 

[Affan]

Thankyou very very very much sir! If I would need any more help for the project, I will ask you Insha Allah.

 

[Affan]

Can we somehow use a larger resistor to make the project? Because resistor of this resistance(R<50ohm) are rare here.

 

[justDIY]

connect resistors in parallel to reduce the total resistance

 

[Krumlink]

Just use an 47 ohm resistor. It is close enough, then the Tolerance should help out too.

 

[Affan]

Thank you very much. My teacher has approved the circuit diagram and now I will implement it.

 

[Cry_Wolf]

Can we somehow use a larger resistor to make the project? Because resistor of this resistance(R<50ohm) are rare here.

I guess you are in Pakistan

 

[Affan]

Exactly Sir! I am from Rawalpindi, Pakistan. One more question sir. Which one among LM338K and LM340 would be better to implement this 2A dc current source project and why?

 

[Roff]

Just use an 47 ohm resistor. It is close enough, then the Tolerance should help out too.

Krumlink, you should add a smiley when you're joking. I'm afraid our OP took your advice seriously.