Adjustable Constant Current Drive

  • Thread starter graeme.cunningham@googlem
  • Start date
G

graeme.cunningham@googlem

Guest
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
 
graeme.cunningham@googlemail.com wrote:

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 Burke wrote:

graeme.cunningham@googlemail.com wrote:

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
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
 
In article <1156499846.438918.303960@m73g2000cwd.googlegroups.com>,
graeme.cunningham@googlemail.com says...
Paul Burke wrote:

graeme.cunningham@googlemail.com wrote:

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

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
 
graeme.cunningham@googlemail.com wrote:
Paul Burke wrote:

graeme.cunningham@googlemail.com wrote:

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

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
 
<graeme.cunningham@googlemail.com> wrote in message
news:1156420236.347910.56500@m79g2000cwm.googlegroups.com...
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
-
(created by AACircuit v1.28 beta 10/06/04 www.tech-chat.de)
 

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