Hello!
I would like to try and make a constant current source from a switching regulator to power a laser diode. I would also like to be able to adjust the output current in real time via a 0-5V signal from a DAC. Finally, I'd like to offset the output current slightly so that when the modulation signal is low there's still a little bit of current output. This would be used to set the threshold current, as most of these diodes don't do anything till over 50mA or so.
I think this should be possible using a switching regulator, I have used laser drivers in the past that work in a similar way but without the analog modulation.
I think I have something that will work, but would like to see if someone knows a better way. Here is a photo of what I have so far.
On the left is the modulation voltage source, followed by a potentiometer divider to set the main gain, then followed by another divider to drop the scale to 0-1V. On the right is the bias gain, a similar resistor divider from potentiometer. Before summing these two voltages they are passed through unity gain opamps to prevent inbalance between the resistor dividers. This final voltage represents the requested output current. I would like this driver to be able to drive up to 1A, so as configured in the photo 1A = 1V.
On the lower half is the feedback, a pretty simple current sense amplifier configured to output 1V/A.
Now I think I should compare the two voltages, if the target is higher than the feedback voltage I need a higher voltage on the feedback pin on the regulator, and if it's lower I need less. Would a comparitor and some dividers to set the output voltage to match the switching regulator be enough? Or is there a better way? With a basic comparitor circuit I am getting the expected digital output, but what can I do to get a more analog-like feedback?
Thank you for any advise, I have next to no knowledge of this analog stuff!
I would like to try and make a constant current source from a switching regulator to power a laser diode. I would also like to be able to adjust the output current in real time via a 0-5V signal from a DAC. Finally, I'd like to offset the output current slightly so that when the modulation signal is low there's still a little bit of current output. This would be used to set the threshold current, as most of these diodes don't do anything till over 50mA or so.
I think this should be possible using a switching regulator, I have used laser drivers in the past that work in a similar way but without the analog modulation.
I think I have something that will work, but would like to see if someone knows a better way. Here is a photo of what I have so far.
On the left is the modulation voltage source, followed by a potentiometer divider to set the main gain, then followed by another divider to drop the scale to 0-1V. On the right is the bias gain, a similar resistor divider from potentiometer. Before summing these two voltages they are passed through unity gain opamps to prevent inbalance between the resistor dividers. This final voltage represents the requested output current. I would like this driver to be able to drive up to 1A, so as configured in the photo 1A = 1V.
On the lower half is the feedback, a pretty simple current sense amplifier configured to output 1V/A.
Now I think I should compare the two voltages, if the target is higher than the feedback voltage I need a higher voltage on the feedback pin on the regulator, and if it's lower I need less. Would a comparitor and some dividers to set the output voltage to match the switching regulator be enough? Or is there a better way? With a basic comparitor circuit I am getting the expected digital output, but what can I do to get a more analog-like feedback?
Thank you for any advise, I have next to no knowledge of this analog stuff!