Long exposure and small aperture? -----Original Message----- From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] On Behalf Of= Jim Ruxton Sent: Wednesday, September 21, 2016 11:06 AM To: piclist@mit.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 intensit= y with a PIC so I can't use a typical power supply with constant current se= tting and yes the high voltage of approx. 144 volts DC makes that a limitin= g 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 con= trollable via at least 20 kHz PWM. I guess alternatively I could use 4 36 V= olt 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.=20 http://www.meanwell.com/webapp/product/search.aspx?prod=3Dhvgc-320 Also someone asked if I could sync the the PWM to the camera but unfortunat= ely it could be used with different cameras so that would be difficult. Thanks, Jim On 2016-09-20 02:56 AM, rubenjonsson@bredband.net wrote: > Instead of PWM dimming you can use linear dimming. It is basically a=20 > switching regulator at around 300kHz to 1MHz that regulates the=20 > current linearly. You can normally dim linearly down to a couple of=20 > hundred mA, below that you need to PWM dim. > > You can see the difference between linear and PWM dimming in a=20 > datasheet for a led driver. For example TPS92640/1 (which has both=20 > linear and PWM dimming):=20 > > > An alternative is to use a power supply with constant current setting=20 > and just set the current that you want. But 150V might be a limiting=20 > factor here. > > /Ruben > > On Tue, 20 Sep 2016 18:34:58 +1200, "Brent Brown" > wrote: >> Hi Jim, >> >> I don't know what's available in off the shelf PWM drivers. But to=20 >> avoid strobing altogether you may need to consider filtering the PWM=20 >> to supply the LED's with smooth DC current. You don't say what frame=20 >> rate the high speed video is, but it's possible you'd see various=20 >> undesirable effects at almost any PWM frequency if the LED's & camera=20 >> are not synchronised. >> >> Brent >> >> On 20 Sep 2016 at 1:55, Jim Ruxton wrote: >> >>> I was wondering if anyone knows of a high PWM frequency LED driver I=20 >>> could use. I would like to drive 4 Cree CXB3590 COB LEDs in series=20 >>> (36 >>> Vx4 3.6A) . I would like to be able to have a PWM frequency of at=20 >>> least 20 KHz if possible. It would be used with high speed video so=20 >>> the high frequency would be used to avoid strobing. Also I am hoping=20 >>> for an off the shelf driver like the Mean Well drivers , not one=20 >>> that I would design and build. Seems like most of the commercially=20 >>> available drivers have a PWM frequency topping out around 3 Khz.=20 >>> Would it be possible to use one of these drivers, run it full out=20 >>> with a FET in series or shunting the LED string to do the PWMing=20 >>> rather than use the built in PWM function. Curious if anyone has any=20 >>> experience that would send me in the right direction. -- http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/chang= e your membership options at http://mailman.mit.edu/mailman/listinfo/piclis= t --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .