Current Supply Design - Electronic Circuits Projects Diagrams Free

jacobs_ladder · 12th September 2003, 11:19 PM

Project Takes 2 input signals. One 0 to 5V representing desired current, the other 0 to 5V representing the MAX current. The output is linear with respect to the input signal.

I've tried using an op amp voltage to current amplifier but i cannot get it to work properly.

I plan on using a comparator to selector to choose the correct signal to drive the current source. But the current source is what is giving me problems now. Any tips out there. Please feel free to help.

P.S. Driving a Diode Laser.

nettron1000 · 13th September 2003, 03:56 AM

Quote:

I've tried using an op amp voltage to current amplifier but i cannot get it to work properly.

Do you have a schematic of your circuit that you can post ?

Roff · 14th September 2003, 03:14 PM

You need to provide more info.
1. Do you need a current source or a current sink?
2. What is the maximum current?
3. Is the load connected to ground or a DC voltage?
4. What is the highest voltage the output must sustain?

jacobs_ladder · 14th September 2003, 07:58 PM

max load voltage drop is 5V max current is .2A

input range is from 0 to 5 V... the op amp circut is simple and up to .6 V it is perfect... 1V = 40 mA

this is a current source, and the load is connected through a resistor to ground. the resistor controls the amp per volt of the driver amplifier.

EDIT: added schematic

nettron1000 · 14th September 2003, 08:53 PM

Appears to me you need to add a transistor to the output. An Opamp is a voltage gain device while a transistor is a current gain device. Heres an example circuit.

http://www.elecdesign.com/Files/29/2985/Figure_01.gif

jacobs_ladder · 14th September 2003, 09:26 PM

much appreciated. I upped the rails to 15V, added a transistor to the output, and bingo.

Thanks again.

Roff · 15th September 2003, 06:52 PM

Mr. Ladder, I'm not sure what your circuit looks like now, but the one you posted is a voltage source, not a current source. Try running at a fixed voltage for V3 and changing the load. You'll find that the current is not constant, but instead equals V3/R2.
You have the + and - pins on the op amp reversed. This usually works in simulations (I'm not sure why), but it won't work in hardware.

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12th September 2003, 11:19 PM	(permalink)
jacobs_ladder	Current Supply Design Project Takes 2 input signals. One 0 to 5V representing desired current, the other 0 to 5V representing the MAX current. The output is linear with respect to the input signal. I've tried using an op amp voltage to current amplifier but i cannot get it to work properly. I plan on using a comparator to selector to choose the correct signal to drive the current source. But the current source is what is giving me problems now. Any tips out there. Please feel free to help. P.S. Driving a Diode Laser.

14th September 2003, 03:14 PM	(permalink)
Roff	You need to provide more info. 1. Do you need a current source or a current sink? 2. What is the maximum current? 3. Is the load connected to ground or a DC voltage? 4. What is the highest voltage the output must sustain?

14th September 2003, 08:53 PM	(permalink)
nettron1000	Appears to me you need to add a transistor to the output. An Opamp is a voltage gain device while a transistor is a current gain device. Heres an example circuit. http://www.elecdesign.com/Files/29/2985/Figure_01.gif __________________ Two roads diverged into a woods...i took the one less travelled by. R. Frost.

14th September 2003, 09:26 PM	(permalink)
jacobs_ladder	much appreciated. I upped the rails to 15V, added a transistor to the output, and bingo. Thanks again.

15th September 2003, 06:52 PM	(permalink)
Roff	Mr. Ladder, I'm not sure what your circuit looks like now, but the one you posted is a voltage source, not a current source. Try running at a fixed voltage for V3 and changing the load. You'll find that the current is not constant, but instead equals V3/R2. You have the + and - pins on the op amp reversed. This usually works in simulations (I'm not sure why), but it won't work in hardware.