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LM334 constant current source "inverse" design?

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Zero999:

--- Quote from: zdelarosa00 on March 25, 2019, 04:39:10 pm ---Ok. I would go to that LM317 circuit if needed. Thanks.
But I have another doubt...
What if I use an OpAmp to amplify the current source? Is that more stable?

And on another idea: Is it a good idea to put a transistor as active load at RSET in the LM317 adj resistor and change current trought there?

--- End quote ---
No, you can't just replace resistors with transistors, like that.

If you want to use an op-amp, then there are plenty of op-amp constant current circuits.

What are you trying to do?

zdelarosa00:
I really just want a simple to understand circuit for conrtolling a laser diode (OPV300)...
The thing is, I would like it to be as less integrated as possible, I mean, complete 1 voltage regultator 1 set resistor setups totally work but I would like to modulate the brightness fairly quick, and there is I2C digital potentiometers but are not nearly as fast.

So, that is why I was going for the current reference, set resistor, transistor and all components separately, for simplicity I thought of a MOSFET at the output since for me, givenis much more easy to produce a varying voltage to modulate brightness.

How fast? Maybe 400KHz tops or so.

At this point i am not really sure how to proceed.

Zero999:

--- Quote from: zdelarosa00 on March 26, 2019, 10:14:10 am ---I really just want a simple to understand circuit for conrtolling a laser diode (OPV300)...
The thing is, I would like it to be as less integrated as possible, I mean, complete 1 voltage regultator 1 set resistor setups totally work but I would like to modulate the brightness fairly quick, and there is I2C digital potentiometers but are not nearly as fast.

So, that is why I was going for the current reference, set resistor, transistor and all components separately, for simplicity I thought of a MOSFET at the output since for me, givenis much more easy to produce a varying voltage to modulate brightness.

How fast? Maybe 400KHz tops or so.

At this point i am not really sure how to proceed.

--- End quote ---
More questions I'm afraid.

Do you want continuously variable control i.e. be able to set the current from any value between 0mA and 7mA?

Or do you just want to pulse the LED on and off at 400kHz?

How are you controlling this? Presumably a microcontroller.

What power supply voltages do you have available?

How critical is the current regulation?

If all you need is to pulse it at at 7mA, you have a nice stable supply voltage and current regulation is not important, then simply connecting the OPV300 to the output pin of the microcontroller via a suitable current limiting resistor will do the job.

If you need to continuously vary the current between 0mA and 7mA, with a decent level of precision. You need a DAC, clocked a double the maximum frequency of interest and a voltage to current converter. The voltage to current converter can be made with a fast enough op-amp, with sufficient output current capacity.
https://www.allaboutcircuits.com/textbook/semiconductors/chpt-8/voltage-to-current-signal-conversion/
https://www.allaboutcircuits.com/technical-articles/the-howland-current-pump/
http://www.ti.com/lit/an/snoa474a/snoa474a.pdf

zdelarosa00:
OK I'm ready...

1) Continuous control would be useful but I'm almost certain I will just use pulsed modulation.

2)Yes a microcontroller is the source of the modulation, but for experimentation purposes a signal generator can be used.

3)I think power supply voltage is not a problem, +-32v 2A. And +5v 3A. Why is this pertinent?

4)Critical enough to not burn the laser.

5)That uC-DAC-OpAmp Translator sounds like a very good idea, I guess there is no transistor at the output here.

Zero999:
I think you should try connecting the laser diode to the microcontroller output via a resistor.

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