Current Regulator for power supply

[sparky!(Sean)]

I have built me a ac to dc voltage regulated power supply, but now i want a little more out of it and i am wondering if I could build another circuit to where I can control the amps but i have no idea how to do this any help is greatly appreciated

 

[ChrisP58]

Post the schematic of what you have, and we'll see what it would take to add current limit control.

 

[sparky!(Sean)]

This is bascially the circuit that i usedView attachment 64470View attachment 64471

 

[dr pepper]

Making the 317 adustable for both current and voltage is a little tricky, you might be better off with something like a l200 which is deigned for that.

However heres someones project write up for a power supply using 2 317's, one for current limit and another for voltage limit.

http://chemelec.com/Projects/Power-Supply/Power-Supply.htm

 

[Mr RB]

I've often used two LM317s. The first is the current limiter and the second is the voltage regulator. You need to provide 7mA or so more from the current regulator LM317 as you lose a few mA in the second (voltage) regulator.

Assuming that in most cases you don't need to regulate current that precisely and can allow a few mA current error it works fine.

 

[sparky!(Sean)]

Would you use different circuity or the same on the current regulator

 

[Mr RB]

An LM317 current regulator is simpicity itself, you just need the LM317 and one resistor (from Vadj to Vout, which sets the current limit). Then patch the thing in series on the power wire, before your voltage regulator.

I think we need a sticky on making LM317 variables PSUs and dual LM317 current limited PSUs, the same questions seem to come up a lot!

 

[sparky!(Sean)]

Ok thanks so much

 

[sparky!(Sean)]

Ok I am a curious one don't want to bother you but if you do that how does it not act like a voltage regulator and how does it act like current limiter

 

[sparky!(Sean)]

Also i am a little confused still on how to hook it up so i tried my best to draw it out tell me if i am right or wrong and whereView attachment 64533

 

[Roff]

Here is the basic scheme.

 

[harold777]

Hi there, new to Forum, but I think that cct (Post#10), is wrong. My understanding (is/was) you have a fixed R from Output to Adjust and then a variable to Gnd. The fixed Res and variable need to be low values so the chip-current is small compared with the bleed current, but this may be so as make calculating OP voltage easier.

I looked at National Semiconductor who provide a .pdf Data Sheet . . . surely the place for posters to start?

As I come for Britain, there is a tendency to adopt European conventions and the ziz-zag (for resistors) went out about fourty years ago, we use a rectangle and values are designated with R, k, or M, thus a speaker might be 8R0 and the input to a DMM about 20M - this scheme avoids the use of ohm symbol (omega) which is inconvenient to include in a short message, on a sketch, etc.
If you use feint squared paper, it is very easy to get comnponents in a very neat layout, ready for the photocopier which (usually) makes the grid disapear.

I suggest OP has a read of that datasheet and all will be revealed, along with significant parameter worries he'd not thought of.

Is that any help?

PS Post#11 is spot-on as I read it, but I think OP wanted a blow-by-blow explanation....

 

[Roff]

Hi there, new to Forum, but I think that cct (Post#10), is wrong. My understanding (is/was) you have a fixed R from Output to Adjust and then a variable to Gnd. The fixed Res and variable need to be low values so the chip-current is small compared with the bleed current, but this may be so as make calculating OP voltage easier.

I looked at National Semiconductor who provide a .pdf Data Sheet . . . surely the place for posters to start?

As I come for Britain, there is a tendency to adopt European conventions and the ziz-zag (for resistors) went out about fourty years ago, we use a rectangle and values are designated with R, k, or M, thus a speaker might be 8R0 and the input to a DMM about 20M - this scheme avoids the use of ohm symbol (omega) which is inconvenient to include in a short message, on a sketch, etc.
If you use feint squared paper, it is very easy to get comnponents in a very neat layout, ready for the photocopier which (usually) makes the grid disapear.

I suggest OP has a read of that datasheet and all will be revealed, along with significant parameter worries he'd not thought of.

Is that any help?

PS Post#11 is spot-on as I read it, but I think OP wanted a blow-by-blow explanation....

Your LM317 configuration is for a voltage regulator. Have you read the entire thread? After doing so, if you still have questions, see the current regulator schematic on p. 18 in the**broken link removed**.
Come back here if you still have questions.

 

[sparky!(Sean)]

No I get it now when I said I didn't it was directed at mr rb