Hi guys, below is a design I made for a 12V laser driver for a CNC
http://imgur.com/a/rDFcP - schematicv
http://imgur.com/a/FY5nk - reality
ref_pwm is a PWM signal (or if you want... a DC one, you can skip the filter if so) of a few KHz, it's duty cycle sets the reference voltage anywhere in the range of (0-3.3V). [3.3 = max PWM output of your uC]
This sets the the reference for the current loop.
lase (or I guess lase bar lol) pulls down the reference voltage to zero, killing the current in the loop.
RC filters are used to lower the edge on the PWM signals to make it easy for the loop to follow the reference.
the 1K res on the output of the opamp feeding into the gate of the MOSFET makes the load not compleltly capacitive, which the opamp (might) not like, depends on yuur choise of opamps.
Pick something which has common mode input range that goes all the way down to zero (LM324 works) as we are sensing aruond this range
I picked a 1OHM resistor for the sense resistor because it also acts as a degeneration resistor, lowering sensitity of the loops, helping avoid osscilations
I tested it out, works great.
I'm using relay to short the laser when not in use to avoid issues with frying the laser
Vcc = 10~12V (based on your max current)
---------PROS
easy,safe,cheap
---------CONS
bulky,ineffecient
http://imgur.com/a/rDFcP - schematicv
http://imgur.com/a/FY5nk - reality
ref_pwm is a PWM signal (or if you want... a DC one, you can skip the filter if so) of a few KHz, it's duty cycle sets the reference voltage anywhere in the range of (0-3.3V). [3.3 = max PWM output of your uC]
This sets the the reference for the current loop.
lase (or I guess lase bar lol) pulls down the reference voltage to zero, killing the current in the loop.
RC filters are used to lower the edge on the PWM signals to make it easy for the loop to follow the reference.
the 1K res on the output of the opamp feeding into the gate of the MOSFET makes the load not compleltly capacitive, which the opamp (might) not like, depends on yuur choise of opamps.
Pick something which has common mode input range that goes all the way down to zero (LM324 works) as we are sensing aruond this range
I picked a 1OHM resistor for the sense resistor because it also acts as a degeneration resistor, lowering sensitity of the loops, helping avoid osscilations
I tested it out, works great.
I'm using relay to short the laser when not in use to avoid issues with frying the laser
Vcc = 10~12V (based on your max current)
---------PROS
easy,safe,cheap
---------CONS
bulky,ineffecient