hi,
This is what I see using the @Bordodynov TIP120.

Are your LTS Control settings as per this image clip.?
E


Update:
Interesting to note the discontinuity at about 75mSec on both your and my plots.????

 

Hi,
My settings are the same as in the image you posted, maybe its related to the fact we are not using the same TIP120.
The discontinuity after 75msec is really strange, i think it looks better in my image from some unknown reason.

More interesting than the fine adjustments, from your experience how you will tackle this kind of switching? maybe i need to take another approach?

Thank you

 

hi 89,
For a discussion reference, do you have sketch of an Idealised waveform you would like to create.?

E

 

Hi,
My main goal is to create constant current source between 0-200mA, controllable by 0-3.3V analog input from MCU,
And can be modulated (ON/OFF only) by square 0/3.3V PWM signal (changeable frequency up to 10khz and DC 0-100% from MCU).

V3 In my schematic should provide the analog 0-3.3V (MCU PWM with MCP4725 PWM to analog)
and V2 should modulate the signal by PWM from MCU.

I'm not sure about high side switching / low side switching , BJT/MOSFET...

Thank you,

 

hi 89,
The 22n cap on the output of the U3 OPA was causing instability in the OPA.
Modified the TIP input drive and feedback loop.

E

 

Dear Eric,
Thank you for your help .
As far as my understanding and checks, most likely that switching will be done better with MOSFET indeed.

I tried today connecting MOSFET gate driver(TC4420) from my MCU to the FQP30N06L in order to fully activate it from the MCU's 3V3 , and although I added all the required bypass capacitors and resistors it involved quite significant noise taking into consideration the laser sensitivity.

I already purchased some smaller MOSFET and until then, I guess the easiest way will be to extract the PWM signal from industrial function generator instead of my MCU.

Beside that, everything seems to work just fine

Thank you!

 

hi 89,
Thanks for letting me know how you are progressing with the project.

Please keep me upto date on the future development of the project.
Eric