Drive PWM laser using external mosfet module?

Reefwarrior

Hi all,

Is it possible to drive a PWM laser using an external mosfet module, directly from a Duet2?

Can something like this work?

https://www.aliexpress.com/item/4000609702577.html?spm=a2g0o.9042311.0.0.27424c4dLwaDTK

Rgds
Tinus

o_lampe

@reefwarrior
If you want to switch power on/off, they should work. But for PWM laser control, I'd use a level shifter. They switch faster with shorter rise/fall time. That makes the output clear and sharp.

Reefwarrior

@o_lampe Are you referring to a logic-level shifter?

o_lampe

@reefwarrior Yes, I just checked the supplier. They should have them, but probably in a lot of 50-100 PCBs as it seems.

Reefwarrior

@o_lampe Can you perhaps advise as to how I should connect what?

Reefwarrior

So there are 3 connectors on the diode laser. + / - / TTL

As soon as voltage is applied (12V) to + and -; the laser 'fires'.

Can this thing be driven by the duet board? And if so, how?

dc42

@reefwarrior the TTL input is usually a PWM-capable input for controlling the laser. This can be driven directly from the LASER/VFD output of a Duet 3 (including Duet 3 Mini) or from a PWM output of a DueX board or Expansion Breakout board.

If you have a Duet 2 without one of those expansion boards, then the recommended approach is to use a 74HCT02 gate to level-shift one of the expansion connector heater outputs. See the "Duet 2 Additional Hardware" tab at https://docs.duet3d.com/en/User_manual/Machine_configuration/Configuration_laser for details. If you find that too hard then you can purchase the Expansion Breakout Board.

Reefwarrior

@dc42 Thank you for the help!

SupraGuy

Very timely, as I was just looking for this information myself to drive a PWM laser from a Duet 2 Wifi.

I ended up purchasing boards from JLCPCB.com, and they appear to have a minimum order quantity of 5 (And for some reason, it's cheaper to buy 15.) ... So I have 15 on the way, populated with the SMT components C1 and U2. It was a bit unclear as to which side H1 connected to. It looks like it should go on the bottom of the board, though I'm not sure which header it connects to. If it's on the expansion board, that could be a problem for me, and I might need to figure some other stuff out, but it appears to occupy pins 1-8 of the 50 pin expansion header.

Anyway, I've got the boards on the way, and 8 pin headers coming separately. I'll probably just solder wire to the board for the DC in and laser out, since neither JLCPCB nor Digikey seemed to have appropriate connectors in stock when I looked.

For what the extra cost, maybe I should have just bought a Duet 3 6HC instead.

ktapper

@supraguy You got any extra printed boards?

Denis

@dc42 If my laser is 24 volts, can I connect to the PWM from the LASER/VFD output and power it from the 24v input or from the heater?

dc42

@Denis said in Drive PWM laser using external mosfet module?:

@dc42 If my laser is 24 volts, can I connect to the PWM from the LASER/VFD output and power it from the 24v input or from the heater?

If the laser accepts a 5V or TTL level PWM input signal, then you can connect the LASER/VFD output to that and the laser power supply voltage is immaterial. Make sure that you have the Duet and laser grounds connected.

olliss

@dc42 said in Drive PWM laser using external mosfet module?:

@Denis said in Drive PWM laser using external mosfet module?:

@dc42 If my laser is 24 volts, can I connect to the PWM from the LASER/VFD output and power it from the 24v input or from the heater?

If the laser accepts a 5V or TTL level PWM input signal, then you can connect the LASER/VFD output to that and the laser power supply voltage is immaterial. Make sure that you have the Duet and laser grounds connected.

I had out9 connected to pwm. and the power for the laser connected to the out1 connector, because I wanted to turn the power on/off with it. I tested the laser and everything seemed to work fine until I realized that even though out1 is off my diode laser fan still runs.
Luckily nothing seems to have broken.
so did i understand correctly that i can't control the laser power directly from the duet board when i want to turn it on/off?
Maybe I should put a relay in between.

T3P3Tony

@olliss the output connectors switch the ground side, not the power supply side so that wont work. you can put a external switch (like a relay, SSR etc) in between to turn off the power.