How to convert a Adjustable Reg. to auto adjust

[TKS]

I have found a Usefull LM regulator (LM138) wich will give me 5amps.
the problem is it is adjustable sow it means it doesn´t sees ground??

Is it true that if the input voltage changes on the part, that the output is also changed????

Wich little chip could make it auto adjustable?
An opamp maybe?

could someone draw me up a small sheme?

Tks

 

[Nigel Goodwin]

I have found a Usefull LM regulator (LM138) wich will give me 5amps.
the problem is it is adjustable sow it means it doesn´t sees ground??

Is it true that if the input voltage changes on the part, that the output is also changed????

If it DID, then it wouldn't be a regulator! - don't worry about it!, it's a variable REGULATOR - the resistors set it's output voltage, regardless of the input voltage (assuming it's within a suitable range).

 

[TKS]

ok nigel but i thought of a setup where the input voltage is stable..

and this component just took away a given voltage of it.

At least i´m very easy done with the question

is it true tha that if i add a BC transistor Npn from the adjust pin after the resistance to ground that i have a enable / disable switch??

Thanxs

 

[Nigel Goodwin]

ok nigel but i thought of a setup where the input voltage is stable..

and this component just took away a given voltage of it.

At least i´m very easy done with the question

is it true tha that if i add a BC transistor Npn from the adjust pin after the resistance to ground that i have a enable / disable switch??

Yes, you can set it to it's lowest possible output (about 0.7V or so?), it was often done for standby mode in TV sets.

 

[TKS]

thanxs!

i´m sorted now i need to find a source for it!

 

[eng1]

is it true tha that if i add a BC transistor Npn from the adjust pin after the resistance to ground that i have a enable / disable switch??
Thanxs

Are you going to use the transistor as a digital switch? When the transistor is off the current has no path to ground and the IC acts as a current source.