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Author Topic: PWM Control For Laser Diode  (Read 1826 times)
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Elysion
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« on: January 06, 2015, 06:28:54 18:28 »

Hi All,

I bought a 2w. powered 445nm. laser diode from the below link.

http://www.ebay.com/itm/2W-Copper-445nm-M140-Blue-Laser-Module-W-X-Drive-405-G-2-Glass-Lens-/180950109519?pt=LH_DefaultDomain_0&hash=item2a21778d4f

I use it on my DIY cnc to cut stencils. I use relay for controlling it but I want to use pwm signal to control it.

It has its constant current driver on it. I don't want to take it out so in front of this CC driver, I want to put a pwm controlled voltage changer.

Driver begins to run the LD (Laser Diode) after 4.5 volt up to 8.4V max. This means I have to shift at range of (0V or 4.5V) <-> (8.4).

What do you suggest for this control? Sorry for my bad English.

Thanks,
Oguz


 
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Kain
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« Reply #1 on: January 06, 2015, 07:27:01 19:27 »

A simple DC/DC buck converter would allow you to step down 12VDC to whatever you need it be. I am not sure if you are trying to build the voltage controller or buy one. COTS buck converters will be cheaper than trying to make your own. For instance, Texas Instruments PTN78060WAZT can do what you need. The adjusting element is 1 resistor which could be a potentiometer. Are you planning on using automatic gain control for the laser or manually adjusting it?

Georgi
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CocaCola
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« Reply #2 on: January 06, 2015, 09:01:35 21:01 »

You can buy 3W PWM LED driver modules on Ebay cheaper then you can realistically build them, simply put a voltage divider on the module to control maximum output and you should be golden...
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cncbasher
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« Reply #3 on: January 06, 2015, 10:38:18 22:38 »

perhaps one of these drivers
http://www.ebay.co.uk/itm/Laser-diode-driver-0-5A-100kHz-ANALOG-TTL-405nm-445nm-635nm-650nm-808nm-3-12V-/231440680711
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CocaCola
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« Reply #4 on: January 06, 2015, 11:46:00 23:46 »


Good #%^#$%& $50 USA? EEK!

The OP didn't post design specifics or specific needs, but anyway...

A cheap option is to skip PWM and simply use something like this instead, both voltage and current control for dirt cheap...

http://www.ebay.com/itm/LM2596S-DC-DC-Constant-Current-and-Voltage-Adjustable-Module-LED-Driver-B-S5-/281360424522

Or PWM modules like this...

http://www.ebay.com/itm/DC12V-DC24V-36V-48V-52V-PWM-DC-Motor-LAMP-LED-Speed-Controller-Driver-Governor-/290943263920

http://www.ebay.com/itm/SG3525-Adjustable-Frequency-100-400kHz-PWM-Controller-Module-Professional-/351251705028

BTW those are not recommendations or anyway reflective of the totality of what can be found all over Ebay, just some examples I snagged...
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Elysion
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« Reply #5 on: January 12, 2015, 10:49:42 10:49 »

Hi,

Thank you very much for the responses. ı'll try some and feedback here for future references.

Oguz

Posted on: January 08, 2015, 08:39:07 08:39 - Automerged

Hi,

I don't want to trust low pass rc filters done with opamp so I'll use a pic which will meet the pwm signal and turn it to an analog dc signal over a spi dac (mcp4921) and drive a single supply, rail to rail opamp(#1) and this opamp will drive OP548 power opamp (#2).

I'm not sure about driving #2 power opamp with #1 buffer. It seems as gain control unit and very low drive current needings of #2 doesn't require #1. When the parts arrived, I'll try. Will give feedback for the future reference.

thanks
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kreutz
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« Reply #6 on: January 12, 2015, 11:35:27 23:35 »

I am sorry to tell you that placing a Voltage regulator in series with a current source will do absolutely nothing (from the point of view of controlling the diode current/power), unless you set up a voltage below the compliance value for your current source, in which case, the current regulation will not work anymore. What you might want to get is  a "voltage controlled current source" which is a completely different design.

If your goal is to get a voltage in the compliance range for your diode driver circuit, then you don't need a voltage regulator, any rectified voltage supply which can supply 6Vdc @ 2Amps will do.

« Last Edit: January 12, 2015, 11:45:00 23:45 by kreutz » Logged
solutions
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« Reply #7 on: January 13, 2015, 02:54:39 02:54 »

Just put a switch (aka MOSFET) between the current source and the diode. It's not rocket science - LEDs are most precisely controlled by current, not voltage, and you don't need to, and should not, be mucking around with "voltages"....anywhere.

Just because you measured a change in voltage doesn't mean that is what you control. Fastest way to let the functionality-smoke out of your diode.

You are also making this waaaay too complicated for a toy - just change the cutting speed and leave the laser alone.
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Gallymimu
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« Reply #8 on: January 14, 2015, 02:15:50 02:15 »

Also be careful, laser diodes are pretty sensitive to voltage and current overshoot.  Quite easy to blow them up.

This is probably not an issue since it has a driver built in. BUT, by virtue of having a driver built in may make PWM virtually impossible.  It may have enough capacitance internally that PWM at anything but a super low frequency may just piss off the Buck converter.
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Droneman1982
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« Reply #9 on: February 10, 2015, 04:12:11 16:12 »

Why don't want to use a simple linear regulator? Is it portable or stationary? If it is stationary you can simply use d LM317 in constant current mode with some basic filtering at the input ad a good output capacitor. Just remember to never connect the diode with the supply already on (also put a bleeder resistor on the output capacitor) or you will blow the diode.

For portable uses i remember Flexdrive, very clever design and very compact, but quite expensive!

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kreutz
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« Reply #10 on: February 10, 2015, 07:43:13 19:43 »

You can always put a power logic gate Mosfet in parallel with the Laser diode (at the output of the current regulator circuit) and divert the diode current to ground, apply PWM to the mosfet gate. IRL540 will work. This is the cheapest and simpler solution.
« Last Edit: February 10, 2015, 08:08:16 20:08 by kreutz » Logged
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