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Adjustable Constant Current Drive

Hi

I'm trying to design an adjustable constant current drive to supply a
current of 250mA.

I've been trying to use OP amps but have been running into problems as
I need to limit the supply voltage to +/- 5v

Any help would be much appreciated.

G
 
P

Paul Burke

Jan 1, 1970
0
I'm trying to design an adjustable constant current drive to supply a
current of 250mA.

I've been trying to use OP amps but have been running into problems as
I need to limit the supply voltage to +/- 5v

Is the load floating or grounded? What resistance/ impedance are you
driving? What frequency response do you need?

Paul Burke
 
Paul said:
Is the load floating or grounded? What resistance/ impedance are you
driving? What frequency response do you need?

Paul Burke

Its for driving an experimental LED. Not really concerned with
frequency response. As long as I can get 250mA(which can be adjusted,
so I can check a range of drive currents) in there from that supply
voltage and not use any expensive components I'll be happy.

Thanks

Graeme
 
J

James Beck

Jan 1, 1970
0
Its for driving an experimental LED. Not really concerned with
frequency response. As long as I can get 250mA(which can be adjusted,
so I can check a range of drive currents) in there from that supply
voltage and not use any expensive components I'll be happy.

Thanks

Graeme

Look at the NS LM10.
Pretty should work just fine and you will not even need the negative
supply. Gives you a 200mV Vref and an op amp, to use as an error amp,
all in an 8 pin DIP.

Jim
 
L

Leon

Jan 1, 1970
0
Its for driving an experimental LED. Not really concerned with
frequency response. As long as I can get 250mA(which can be adjusted,
so I can check a range of drive currents) in there from that supply
voltage and not use any expensive components I'll be happy.

Thanks

Graeme

You can use an LM317 voltage regulator as a variable current source.
Details are in the data sheet. Another technique is to vary the voltage
to the base of an NPN BJT with the LED between the collector and the
positive supply. This will provide a constant current to the LED,
depending on the base voltage.

Leon
 
J

John Jardine.

Jan 1, 1970
0
Hi

I'm trying to design an adjustable constant current drive to supply a
current of 250mA.

I've been trying to use OP amps but have been running into problems as
I need to limit the supply voltage to +/- 5v

Any help would be much appreciated.

G

As Leon mentions, maybe this kind of arrangement ...

o-------------------o-------5V
| |
.-. .-.
| | | |4.7 ohm
| | | |
'-'150 ohm '-'
| |
| | PNP Darlington
.-. |< TIP ???
| |<---------------|
| | |\
'-' Pot |
| 100 ohm |
| o
|
.-. |
| | < V Special LED
| | < -
'-' |
| 220 ohm
| o
| |
| | 0-250ma
| |
o-------------------o-------0V
-
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