Building a Current Source with an OpAmp!

[@GuyOuiOui]

Amazing explanations and scientific approach! Keep that amazing energy and passion .

[@EEforEveryone]

Thank you for the Encouragement GuyOuiOui, and thanks for watching!

[@T2D.SteveArcs]

very good that was a lot of words in a row lol best words of the vid tweekage and converse,,, that was really good well done fella, can you show adding a soft start for driving laser diodes

[@EEforEveryone]

Hi Tested to Destruction! Ha, yeah... I guess I started making up some words. :) Absolutely we can talk about adding soft start! As a quick idea, we're about to make a more typical controller, with PID. A simple integrator with a relatively long time constant may be enough to get you moving in the right direction though! More to come there! Cheers!

[@amratsingh5206]

I want to use this circuit to drive bunch of LEDS in constant current. Can I connect the non inverting input of op amp (vref) directly to the GPIO of my microcontroller. To PWM the constant current source. My PWM signal not only varies by duty cycle but also by PWM frequency between 200Hz to 5000Hz very quickly. I can’t low pass filter the pwm output which people are suggesting me to do. How would you approach this scenario? Is it okay to connect it directly?

[@EEforEveryone]

Hello Amrat, a couple thoughts: depending on what "a bunch" means, you might have a lot of power dissipated in a linear current source for that application. If you say that you can't filter the pwm output, I'm guessing that transient response is very important to you. Perhaps consider driving this circuit with a digital potentiometer, or SPI DAC. In fact, some microcontrollers have analog outputs (DACs) built-in! Like everything, this circuit has limits, especially with regard to transient response. I'm not sure if it will directly work for what you have in mind. My best recommendation is to pull the LTspice model (should be linked in the description), change the inputs and outputs for what you're trying to do (string of LEDs, 5kHz pwm input), and see what the stresses look like in the critical components!

[@chinmaykaul7746]

Hi, i wanted to create a 1A current source at 70khz, what changes do i need to make in this circuit?

[@EEforEveryone]

Hello! One of the biggest changes you'll need to make is generating a modulated current source. This is configured with a DC reference. The second biggest change is being able to generate a positive and negative voltage, where this is currently configured to only apply positive voltage. The end schematic may end up looking very different!

[@power-max]

But an opamp is an (imperfect) integrator. It should have very high gain at low frequencies, but begin rolling off -20dB/dec (a classic integrator response) after 10Hz or so. There should be a lot less steady-state error. I think the problem may be common mode voltage range of the OP07 or maybe the input offset voltage? It's an old part. I have some OP27's and OP37's around and I think those are supposed to be precision parts. Perhaps try connecting a resistor network to the offset null pins.

[@EEforEveryone]

Interesting thoughts! I've long since left this sim collecting dust, but great point about how there continues to be evolution and improvement in components. I'll have to give some higher-performance parts a try!

[@RLDacademyGATEeceAndAdvanced]

Good

[@EEforEveryone]

Thank you1