I was used the normal op amp to replaced it, but I still can't find the potentiometer, it's weird, I used the pot before, but I can't find it after I was updated a couple times later.
The op amp is at the\lib\sym\opamp\opamp.asy

@ScottWang, Thanks! I did find an opamp2 too. I did find a potentiometer from the LT Spice's yahoo group.

 

@ScottWang, Thanks! I did find an opamp2 too. I did find a potentiometer from the LT Spice's yahoo group.

I don't have a Yahoo Email, but I found this wonderful webpage for the Lib of LTspice --
LTspiceIV-library Library Listing Expanded.

 

Nice! Thanks @ScottWang

 

I don't have a Yahoo Email, but I found this wonderful webpage for the Lib of LTspice --
LTspiceIV-library Library Listing Expanded.

Excellent link for the rest of us too, Scott. Thanks!

 

Excellent link for the rest of us too, Scott. Thanks!

You are welcome, so you also have playing the LTspice?

 

Sorry, lost this thread.

 

Sorry, lost this thread.

@ronv Any more commonly available equivalent for the OPA743? Can't seem to find it in my part of the world.

 

It's not to fancy.
It needs to be able to sense at ground. So common mode range must include ground. It's nice if the output can drive at least 10ma to ground.
Not real fast, but a gain bandwidth of say 6 to 10 Mhz.

 

OK. Did some research on the local market and couldn't find it. Would either of these work?

OPA337 (this one is 3MHz)
TSV912IST
MCP6291

 

OK. Did some research on the local market and couldn't find it. Would either of these work?

OPA337 (this one is 3MHz)
TSV912IST
MCP6291

That's a bummer. They won't work on a 12 volts supply.
I bet you can find a LM358 or LM324.

 

@ronv, thanks! Those are available quite easily. I do have a 5V supply too. Come to think of it, I could use the 5V to power one of these and the laser.

 

@ronv, thanks! Those are available quite easily. I do have a 5V supply too. Come to think of it, I could use the 5V to power one of these and the laser.

5 volts may not be enough with the laser needing 4.5.

 

Right. 12V it is. I'm gonna try this out with the LM358. Will keep you posted.

 

I simulated the schematic in TINA-TI (attached the image and the TSC file here) since I did not have many of the libraries in LTSpice and the ones I installed weren't exactly working right. Now without the PWM source at the non-inverting terminal of LM358, the circuit simulates just fine with a constant current of 1.4A. However, with the PWM source in (0-5V at 1ms intervals. This essentially would simulate the laser switching ON and OFF from the MCU), the load current shows about 3A . What am I missing here?

 

I simulated the schematic in TINA-TI (attached the image and the TSC file here) since I did not have many of the libraries in LTSpice and the ones I installed weren't exactly working right. Now without the PWM source at the non-inverting terminal of LM358, the circuit simulates just fine with a constant current of 1.4A. However, with the PWM source in (0-5V at 1ms intervals. This essentially would simulate the laser switching ON and OFF from the MCU), the load current shows about 3A . What am I missing here?

The pwm signal needs to be an open drain output from the MCU - no active pull up.
Be careful with the 15 nf cap to ground. It may cause instability.

 

you need a kind of power electronics circuits . you can use either buck converter and boost converter. if you are using buck converter, you can design constant current source buck converter using uc3842 pwm controller IC using it as a constant current mode. you may use this link http://microcontrollerslab.com/led-driver-using-uc3842/ as a reference where author design constant current buck converter for LED driver.
let me know if you have any question

 

The pwm signal needs to be an open drain output from the MCU - no active pull up.
Be careful with the 15 nf cap to ground. It may cause instability.

Ah I see, but then I'd have to make the Arduino pin as an INPUT pin to disable the pull ups. Would something like this work? (attached)

 

you need a kind of power electronics circuits . you can use either buck converter and boost converter. if you are using buck converter, you can design constant current source buck converter using uc3842 pwm controller IC using it as a constant current mode. you may use this link http://microcontrollerslab.com/led-driver-using-uc3842/ as a reference where author design constant current buck converter for LED driver.
let me know if you have any question

Thanks. I think there are simpler chips available with fewer and cheaper components. Such as AP65200 and ST1CC40. The idea here is to learn by designing more fundamental stuff.

 

Ah I see, but then I'd have to make the Arduino pin as an INPUT pin to disable the pull ups. Would something like this work? (attached)

That would work, but you need to remove the 20K so the 2007 can pull the + input of the op amp all the way to ground to shut it off.

 

Awesome! Thanks @ronv.