# high power strobe light



## mikeruth (Feb 5, 2015)

Good day folks new to this forum and I had ran a search using the criteria of STROBE and PULSE and got no where so here I am asking for some help. 

Preface on my quest. I have been using some old cheap *xeon flashers*. They flash about once every second. They are dirt cheap at $5.50 but are not rated for continuous duty. I need a minimum run time of 12 hours and in some cases 24/7. They are rated at 12 volts input. I've been using a 120VAC to 14 volt DC , 5 amp power supply. The flash tube is of course mounted on the PCB and I just mount the unit facing down from a ceiling and I get the effect I need. Covers a pretty good area(about the size of a two car garage) with a nice bright flash. Unfortunately even cutting the run time back to about 8 hours a day they fail within a couple weeks. 

So my quest has been to replicate this using today's modern high(er)power LEDS. So far I started out by building a basic 555 timer circuit and incorporated a N-Chanel MOSFET on the output. I tweaked this to have a very short pulse time. It's flashing at roughly once every two seconds. I haven't taken a temperature reading but I can just barely feel a slight warmth on the back of the LED heat sink. Oh this is a 5 WATT STAR *This one. *I don't have any additional heat sink on it. I actually have a 5 Watt unit running now that is working pretty well for the past 7 days. Schematic is at the bottom of this post. 

Ok so what I'm concerned about is how to best incorporate a LED driver when I step this up to a 50 or 100 watt LED. The 5 watt works but is no where near the flash that the xeon lamp was and again that's where I want to be. Should I be just looking at some type of PS that meets the roughly 36 volts 3.5amps of a 100W LED? I'm really not sure if a 50 Watt LED will do. I'm going to try it cause that would certainly be cool if I could get away with that. I just have to see in real life and real condition what it looks like flashed. 
Lastly, looking at the pulse strip below, and I know this is guessing right now, but just how much less of a heat sink might I be able to get away with since the duty cycle is so short>? I can always just sink one up and then start reducing it but your ideas or thoughts would be appreciated. 

Schematic- Variables have now been replaced with fixed units. 




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Pulse screen shot



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## Steve K (Feb 6, 2015)

a few comments on the design:
- you may want something to limit the current through the LED. It looks like either the mosfet resistance or the limited output ability of the power supply might be doing it now.
The 555 would benefit from having a bypass cap on the power pin. 0.1uF is typical. 
It might be a good idea to have a large cap from the anode of the LED to ground. The cap could provide a lot of the current surge that the LED requires. This would permit the use of a less powerful power supply. 

You should be able to calculate the power being used in the LED and size the power supply to provide the average required current. Further calculations should let you choose the right size of capacitor to provide the pulsed current that you need to have delivered to the LED.


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## mikeruth (Feb 6, 2015)

Steve K said:


> a few comments on the design:
> - you may want something to limit the current through the LED. It looks like either the mosfet resistance or the limited output ability of the power supply might be doing it now.
> The 555 would benefit from having a bypass cap on the power pin. 0.1uF is typical.
> It might be a good idea to have a large cap from the anode of the LED to ground. The cap could provide a lot of the current surge that the LED requires. This would permit the use of a less powerful power supply.
> ...



Thanks for the suggestions, I didn't put the cap on the power pin as I had seen so many 555 timer circuits without, certainly not a big deal and or expense. 
Good point on the large cap to the LED. I'll give that a go right away. I'm sure that will be more desirable one a 50 or 100 watt led is in there. 
I was a bit concerned about the initial inrush current, I believe spec was about 7 amps albeit for 10ns. 

Any one else?


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## Steve K (Feb 6, 2015)

inrush current.... yeah, that's something to consider. If the power supply is well designed, it might mind it. You could add a resistor of one or two ohms in between the power supply and the cap. Or add a current regulator circuit, although that will eat up some voltage. A polyfuse (also called a resettable fuse) might be good too. It's certainly worth the effort to add the cap, though. It can supply many amps of current and relieve the power supply of the need to produce that high level of instantaneous current.


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## more_vampires (Feb 6, 2015)

Steve, don't know if to lol or cry... Probably just have a seizure. My medicine is illegal in my state.


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## Steve K (Feb 6, 2015)

more_vampires said:


> Steve, don't know if to lol or cry... Probably just have a seizure. My medicine is illegal in my state.



I'm really not sure how to interpret this... I'll just assume that it's good??
In the meantime, I hope that you decide to LOL... it's probably better for you.


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## BVH (Feb 6, 2015)

I'm just curious. To the Op - does the effect created by the visible ramp-up, ramp-down and longer duration of the flash of the LED approximate the effect of the flash of the flash tube strobe? I would think that there is a fair amount of visible ramp-up and ramp down light produced by the LED that would tend to make the LED flash not nearly as effective/sharp as the flash tube?

To the experts - wouldn't the use of a driver be far easier on the LED and maybe extend its' life?


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## mikeruth (Feb 6, 2015)

BVH indeed there is the ramp up and I hate it but I'm not sure how else I can pulse a high power LED more effectively getting as much of the "flash" as I can. Indeed a Xeon strobe has a nice crisp sharp Flash. 

I'm totally open to any suggestions. I'm no EE that's for sure.


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## BVH (Feb 6, 2015)

I don't know your use or budget but aren't there commercial grade units available with much higher life times than what you're using now? To me, a strobe should be a real strobe due to the crispness of the flash as you describe it. An example: If you've ever seen "Runway End Identifier lights" at the end of the runway, they are true strobes and can be seen from 10's of miles distant. They are very eye-catching. I'm into short arc lamps and as such, when I search for SA lamps, I see lots of commercial flash tubes and some power supplies on Ebay. From Cermax, Oriel/Newport/Excelitas and other mainstream mfgs. It certainly seems that you have the electronics skills to put something together from individually purchased, commercial grade products. I do just that with used, Oriel/Newport/Cermax SA lamps and power supplies and have had nothing but good luck with all my used equip purchases off Ebay.


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## FRITZHID (Feb 7, 2015)

Bvh is absolutely correct. A high quality xenon strobe should last for many many hrs.
Look at the older aerial marker lights, they strobed for years before bulb failure.
They should be fairly easy to find and really shouldn't be that expensive.
The electronics in the strobe PS are fairly simple as well, therefore easy to modify (fps).
Not to mention you can find some really big strobe tubes!


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## SemiMan (Feb 8, 2015)

BVH said:


> I'm just curious. To the Op - does the effect created by the visible ramp-up, ramp-down and longer duration of the flash of the LED approximate the effect of the flash of the flash tube strobe? I would think that there is a fair amount of visible ramp-up and ramp down light produced by the LED that would tend to make the LED flash not nearly as effective/sharp as the flash tube?
> 
> To the experts - wouldn't the use of a driver be far easier on the LED and maybe extend its' life?




There will be virtually no ramp up on the LED and realistically virtually no ramp down either. The issue is the massively lower level of light output of the LED.

Good flash tubes will last 1 billion flashes, or about 4 years at 1 per second. I would expect that life goes up if you run them at reduced power.


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## DIWdiver (Feb 8, 2015)

Wow! You're lucky you haven't fried something yet. Using a 5A power supply to run a 700 mA LED, with no driver and lots of excess voltage is a seriously poor design. You're pushing the LED at least 7 times what it was designed for, possibly substantially more. A 5 ohm resistor should limit the current to a much more modest overdrive of 100% over max (about 1.4A instead of 0.7A).

Adding a large cap from the anode to ground would only (potentially) make the overdrive worse. Of course you'd need around 1,000,000 uF (1F) to even begin to make a dent in it.

I don't know why you'd see ramp-up or ramp-down. Given your circuit, the FET should turn on in about 1 microsecond, and turn off in several microseconds. Unless you are overheating the LED so much that it's output drops noticably.


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## Steve K (Feb 8, 2015)

has there been any mention of the pulse width? I'm assuming that, roughly speaking, the pulse should be 1ms or less.

I'm also assuming that the pulse frequency would be more than every few seconds... 

I'm inclined to agree with DIWdiver.. there is certainly room for improvement, and I don't see an obvious reason for a ramp up or down. Can MikeRuth show us photos of the circuit or how the ramp up time is measured?


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## DIWdiver (Feb 8, 2015)

The second pic in post #1 shows roughly 100 mS pulse width, a little less than 0.5 Hz. This is consistent with the circuit diagram posted.

Obviously, this is pretty long for a strobe pulse, but he's just experimenting for now. To get really low duty cycle, it's best to use two '555s, one for the short on time, and one for the long off time.

I know that LEDs are now used for camera strobes. Anybody know anything about the specs? I know that back in the dark ages we used 1/125 sec shutter speed for flash, which would equate to 8 mS, but the flash was expected to turn on after the beginning and turn off before the end of that time.


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## SemiMan (Feb 9, 2015)

DIWdiver said:


> The second pic in post #1 shows roughly 100 mS pulse width, a little less than 0.5 Hz. This is consistent with the circuit diagram posted.
> 
> Obviously, this is pretty long for a strobe pulse, but he's just experimenting for now. To get really low duty cycle, it's best to use two '555s, one for the short on time, and one for the long off time.
> 
> I know that LEDs are now used for camera strobes. Anybody know anything about the specs? I know that back in the dark ages we used 1/125 sec shutter speed for flash, which would equate to 8 mS, but the flash was expected to turn on after the beginning and turn off before the end of that time.




They are used for cell phone strobes, not real cameras. They really are not what I would call strobes, more like a light. They result in very long shutter times.

The 1/125 second is not the strobe time, it is the strobe sync time. The flash will happen sometime in that 1/125 second. A major reason for that is the mechanical design of the shutter that does not allow fast shutter speeds synced with the flash. 

The actually flash time is in the tens of microseconds typically .... and hundreds of thousands or millions of lumens.

Semiman


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## mikeruth (Feb 9, 2015)

Once again thanks to everyone that has so graciously provided some input. DIWdiver, I think you may have confused my preface. That power supply was being used on the Cheapo Strobe unit I had purchased from All Electronics. 
I have done some research now on the traditional strobes using Xeon tubes. Indeed I may have actually found a product from Berket specialty lighting. *This unit *in theory will do exactly what I need, although I have not contacted them yet to find out pricing. Pricing is an issue as I am looking to compete with a similar product that sells for $180.00, with replacement bulbs in the $70.00 range. I really wish I could just come right out and tell you what it is but, the lawyer says no. 

I'm still not giving up on the idea of using an LED. Again I haven't personally seen the brightness of 50 watt or 100 watt led yet. I'm going to order a couple of them this week. 
I know my Nitecore EC20 flashlight lights a room pretty substantially when pointed at a ceiling so one of these just might be possible. 

Once again Thank you everyone.


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## LedTed (Feb 9, 2015)

BVH said:


> I'm just curious. To the Op - does the effect created by the visible ramp-up, ramp-down and longer duration of the flash of the LED approximate the effect of the flash of the flash tube strobe?



Just a note: Persistence and beam types would be different between LED and Xenon sources.


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## SemiMan (Feb 9, 2015)

LedTed said:


> Just a note: Persistence and beam types would be different between LED and Xenon sources.



Persistence?


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## Steve K (Feb 10, 2015)

A bit of background info, in case there are others who know just a little about xenon strobes but are interested in making a LED version...
(like me).

the wiki page has some info on the basic characteristics that I found helpful. 
https://en.wikipedia.org/wiki/Strobe_light
"A typical commercial strobe light has a flash energy in the region of 10 to 150 joules, and discharge times as short as a few milliseconds, often resulting in a flash power of several kilowatts."

At the low end of the range, a 10 joule strobe that lasts 1ms still has an instantaneous power of 10kW! Getting that sort of peak power out of LEDs doesn't seem practical, even if you assume that an LED could handle a peak pulse power several times the continuous rating.


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## SemiMan (Feb 10, 2015)

Think much faster in many cases ... 10s of microseconds for many tens of thousands of watts.

Posted by really crappy Tapatalk app that is questionable wrt respect of personal data.


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