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'[EE] Looking for a high PWM Frequency LED Driver'
2016\09\20@015600 by Jim Ruxton

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I was wondering if anyone knows of a high PWM frequency LED driver I could use. I would like to drive 4  Cree CXB3590 COB LEDs in series (36 Vx4 3.6A)  .  I would like to be able to have a PWM frequency of at least 20 KHz if possible. It would be used with high speed video so the high frequency would be used to avoid strobing. Also I am hoping for an off the shelf driver like the Mean Well drivers , not one that I would design and build. Seems like most of the commercially available drivers have a PWM frequency topping out around 3 Khz. Would it be possible to use one of these drivers, run it full out with a FET in series or shunting the LED string to do the PWMing rather than use the built in PWM function. Curious if anyone has any experience that would send me in the right direction.

Thanks,

Jim

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2016\09\20@023500 by Brent Brown

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Hi Jim,

I don't know what's available in off the shelf PWM drivers. But to avoid strobing altogether you may need to consider filtering the PWM to supply the LED's with smooth DC current. You don't say what frame rate the high speed video is, but it's possible you'd see various undesirable effects at almost any PWM frequency if the LED's & camera are not synchronised.

Brent

On 20 Sep 2016 at 1:55, Jim Ruxton wrote:

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2016\09\20@024322 by Jim Ruxton

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Thanks Brent,

I could filter the PWM but I would also like to be able to change the intensity fairly quickly as well which is another reason I would prefer using unfiltered PWM.

Jim



On 2016-09-20 02:34 AM, Brent Brown wrote:
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2016\09\20@025637 by rubenjonsson

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Instead of PWM dimming you can use linear dimming. It is basically a
switching regulator at around 300kHz to 1MHz that regulates the current
linearly. You can normally dim linearly down to a couple of hundred mA,
below that you need to PWM dim.

You can see the difference between linear and PWM dimming in a
datasheet for a led driver. For example TPS92640/1 (which has both
linear and PWM dimming): <http://www.ti.com/lit/ds/symlink/tps92640.pdf>

An alternative is to use a power supply with constant current setting
and just set the current that you want. But 150V might be a limiting
factor here.

/Ruben

On Tue, 20 Sep 2016 18:34:58 +1200, "Brent Brown"
<spam_OUTbrent.brownTakeThisOuTspamclear.net.nz> wrote:
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2016\09\20@102918 by Bob Ammerman

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Is there any way to sync the LED PWM with the high speed camera?

~ Bob Ammerman
RAm Systems

> -----Original Message-----
> From: .....piclist-bouncesKILLspamspam@spam@mit.edu [piclist-bouncesspamKILLspammit.edu] On Behalf
Of
> Brent Brown
> Sent: Tuesday, September 20, 2016 2:35 AM
> To: Microcontroller discussion list - Public. <.....piclistKILLspamspam.....mit.edu>
> Subject: Re: [EE] Looking for a high PWM Frequency LED Driver
>
> Hi Jim,
>
> I don't know what's available in off the shelf PWM drivers. But to avoid
strobing
> altogether you may need to consider filtering the PWM to supply the LED's
with
> smooth DC current. You don't say what frame rate the high speed video is,
but
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> your membership options at http://mailman.mit.edu/mailman/listinfo/piclist

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2016\09\21@130548 by Jim Ruxton

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Thanks a lot for the suggestions. I want to be able to control the intensity with a PIC so I can't use a typical power supply with constant current setting and yes the high voltage of approx. 144 volts DC makes that a limiting factor. When it comes down to it ideally I need a constant current supply that outputs at least 144 volts at 3.6 A. This supply then needs to be controllable via at least 20 kHz PWM. I guess alternatively I could use 4 36 Volt constant current drivers . Still wondering however if anyone knows if I could put a FET in series with the LEDs using a driver such as this one. http://www.meanwell.com/webapp/product/search.aspx?prod=hvgc-320

Also someone asked if I could sync the the PWM to the camera but unfortunately it could be used with different cameras so that would be difficult.

Thanks,

Jim


On 2016-09-20 02:56 AM, EraseMErubenjonssonspam_OUTspamTakeThisOuTbredband.net wrote:
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2016\09\21@142639 by Van Horn, David

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Long exposure and small aperture?

-----Original Message-----
From: @spam@piclist-bouncesKILLspamspammit.edu [KILLspampiclist-bouncesKILLspamspammit.edu] On Behalf Of Jim Ruxton
Sent: Wednesday, September 21, 2016 11:06 AM
To: RemoveMEpiclistTakeThisOuTspammit.edu
Subject: Re: [EE] Looking for a high PWM Frequency LED Driver

Thanks a lot for the suggestions. I want to be able to control the intensity with a PIC so I can't use a typical power supply with constant current setting and yes the high voltage of approx. 144 volts DC makes that a limiting factor. When it comes down to it ideally I need a constant current supply that outputs at least 144 volts at 3.6 A. This supply then needs to be controllable via at least 20 kHz PWM. I guess alternatively I could use 4 36 Volt constant current drivers . Still wondering however if anyone knows if I could put a FET in series with the LEDs using a driver such as this one. http://www.meanwell.com/webapp/product/search.aspx?prod=hvgc-320

Also someone asked if I could sync the the PWM to the camera but unfortunately it could be used with different cameras so that would be difficult.

Thanks,

Jim


On 2016-09-20 02:56 AM, spamBeGonerubenjonssonspamBeGonespambredband.net wrote:
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