current drop at lm317 const current source

[kermit]

I googled for a constant current source and came along the lm317.
I both simulated it (in multisim) and built up the simple circuit, but I neither get a constant current when i attach a load!

I followed this circuit: https://www.roboternetz.de/bilder/konstantlm317.gif.
Everything is fine if the circuit remains open, however attaching a load let the current drop significantly.

Do you see any failures in "my" design?

Thanks

 

[Nigel Goodwin]

You don't give any details of what you've done, what the source is, or what the load is.

 

[Willbe]

You don't give any details of what you've done, what the source is, or what the load is.

Ask Boncuk, but I think your battery is backwards.

 

[Hero999]

Yes the battery symbol and terminals don't match.

 

[mvs sarma]

I googled for a constant current source and came along the lm317.
I both simulated it (in multisim) and built up the simple circuit, but I neither get a constant current when i attach a load!

I followed this circuit: https://www.roboternetz.de/bilder/konstantlm317.gif.
Everything is fine if the circuit remains open, however attaching a load let the current drop significantly.

Do you see any failures in "my" design?

Thanks

Get to the data sheet and applications shown there. your doubts would be cleared. Study them, don't test on Multisim!

 

[markhao]

hehe, just make it in the actual... just replace parts if it is blown.

success is a series of failure!

goodluck

 

[Boncuk]

First of all, how did you make the battery symbol? Normally the long terminals are the + connections and the short ones are -.

Using Proteus ISIS the current is constant.

Have a look.

Might be MultiSim has a better supply and simulates the depleting battery as well.

 

[Boncuk]

Oops, nervous finger.

Hint: For currents below 10mA use the LM317L. Its minimum current is 1mA, but might go down to 500µA.

The LM317 requires a minimum current of 10mA. Everything below won't be stable.

 

[Hero999]

I suspect that the problem is that the drop-out voltage is too high for his application.

The LM317 has a drop-out voltage from anywhere between 1.5V to 2.5V depending on the current and temperature, then you have to add on 1.25V for the voltage referance which gives 2.75V to 3.75V. This means that if he's doing something like powering a blue LED from a 6V supply then it won't work.

 

[kermit]

solved

hi guys,
in fact i should have thought twice before actually posting...

first of all: i didnt create the circuit i linked to - i just linked to the resource i used.

second: you are right: i tried to build a perpetuum mobile that is, the consuming power was higher than it actually could be (load was much too high in order to drive my desired current through the it)

thanks for all your help
kermit