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Old 01-16-2012, 06:13 PM #1
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Default DDL driver switch

Hello all,
I'm building a DDL driver which will be turned on and off by a microcontroller. I understand that the power switch must be between the battery and the driver. This is so the lm317 is never operative with no load, correct? For this reason an N-channel Enhancement MOSFET in this configuration WOULD NOT WORK as this would only disconnect the load from the driver.http://www.electronics-tutorials.ws/...tor/tran21.gif(replacing the lamp with the DDL circuit)

Using a P-channel MOSFET will work, however this would be negative logic:http://www.electronics-tutorials.ws/...tor/tran59.gif(laser on when Vg is LOW)

Is there any way to control a DDL driver using a MOSFET with positive logic?


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Old 01-16-2012, 06:50 PM #2
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Default Re: DDL driver switch

If the LAMP is replaced by the DDL circuit, and the DDL circuit is then powering the LD itself, then I don't see the flaw in your first circuit (conceptually). I'm not well versed in the practical use of MOSFETs, but based on my understanding of how they work and what they do, the first approach seems conceptually sound to me.
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Old 01-16-2012, 07:35 PM #3
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Default Re: DDL driver switch

I think its easier to just eliminate the LM317 and use just use a transistor based constant current source and hook it up to your PWM micro-controller.

Here's a link that might help you: The new stuff!! Constant Current Source #1
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Old 01-16-2012, 07:56 PM #4
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Default Re: DDL driver switch

Quote:
Originally Posted by rhd View Post
If the LAMP is replaced by the DDL circuit, and the DDL circuit is then powering the LD itself, then I don't see the flaw in your first circuit (conceptually). I'm not well versed in the practical use of MOSFETs, but based on my understanding of how they work and what they do, the first approach seems conceptually sound to me.
My understanding was that in a DDL driver the LM317 is set up in a constant current mode, adjusting the voltage in order to keep a constant current flowing between OUT and ADJ. Disconnecting ground would turn off the LD, and thus removing the necessary current draw on a lm317. I guess I'm not very familiar with how a lm317 functions though.


Quote:
Originally Posted by Jufran88 View Post
I think its easier to just eliminate the LM317 and use just use a transistor based constant current source and hook it up to your PWM micro-controller.

Here's a link that might help you: The new stuff!! Constant Current Source #1
That sounds promising actually. Thank you. That instructable isn't exactly what you're proposing right? Just a starter point? I adjusting the duty cycle controls the current while the amplitude adjusts the voltage?
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Old 01-16-2012, 08:05 PM #5
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Default Re: DDL driver switch

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Originally Posted by sprocketme2 View Post
My understanding was that in a DDL driver the LM317 is set up in a constant current mode, adjusting the voltage in order to keep a constant current flowing between OUT and ADJ. Disconnecting ground would turn off the LD, and thus removing the necessary current draw on a lm317. I guess I'm not very familiar with how a lm317 functions though.
It should be perfectly safe to kill the GND into the LM317. I think I understand your concern. But by disconnecting GND, you're also opening the the DDL driver's input circuit, so the IC stops doing its work. What you don't want to do is open the DDL's output circuit (to the diode) while it's working.

So you should be fine to disconnect either the Driver+In or the GND.
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Old 01-16-2012, 08:13 PM #6
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Default Re: DDL driver switch



You'll need to calculate for the maximum set current with a sense resistor, R3.
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Old 01-16-2012, 08:53 PM #7
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Default Re: DDL driver switch

Quote:
Originally Posted by Jufran88 View Post


You'll need to calculate for the maximum set current with a sense resistor, R3.
this looks like the best option for me. I'm guessing this will also be pretty efficient, and allow me to control the power of the laser within software. thank you
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Old 01-16-2012, 09:03 PM #8
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Default Re: DDL driver switch

No problem, it's all in the link I posted.
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FS: 3A selectable test loads *IN STOCK* - link

405nm 455 mA BDR-S06J GUIDESMAN (G2 Drive) - link
445nm 1500 mA A140 SOLARFORCE L2 GUNMETAL (FLEXDRIVE V5) - link
445nm 1566 mA A140 SIPIK HK21 (G2 Drive) - link
473nm B&W Tek BWB-10-OEM - 10mW
532nm SKY Lasers DPL - 200mW
638nm 1071 mA GUIDESMAN (AMC7135) - link
638nm 1053 mA SS 26650 (AMC7135) - link

LED Maglite 3D DD SST-90 5700K w/ Aspheric lens - link
LED Maglite 3D XM-L U2 bin - link
LED Maglite 2D Triple XM-L U2-1C bin - link

My DIY LPM - link
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