Need advice for making or buying a l.e.d. strobe lamp

[manoloco]

My friend wants to make a strobe lamp out of leds that is going to be used in a room of about 4x4 meters and 3m of height, are there any shops that carry items like this?, on the other side he is interested in making one himself, any recommendations for emitter and configuration to use?

Thanks!

 

[Lyndon]

What's the strobe rate? I built a strobe that pulses a LiteOn 1W star at a 1Hz rate using a 555 timer chip in free running mode. No resistor/current limiting: I just slam 12V straight into the LED and make sure the duty cycle is low enough to not overheat it.

I'm also designing a PC-based LED controller, but haven't had much time lately to work on it.

 

[Lightingguy321]

Your timer will either be a simple 2N3904 circuit with two one potentiometer or two resistors to set timing and two capacitors which set rate. Other wise you will be utilizing the NE555 timer cicruit. I recommend that the regulator is tied into the circuit before the timer, otherwise (from experience) capacitors on the regulator circuit will interfere with brightness and strobe rate of the LED.

 

[manoloco]

thanks for the replies!, i will forward this data to my friend, him and his uncle are interested in building the strobe, and i surely will follow so i can learn something

please any advice on buying or making a regulator circuit?

 

[Lyndon]

The circuit I described doesn't need a regulator. A 555 will run at up to 18V and the current through the LED is controlled by adjusting the duty cycle of the 555 which is set by the ratio of two resistors. It is the standard NE555 "free running" circuit that can be found by googling any of the 555 datasheets.

 

[VanIsleDSM]

Exposing the LED to 12v for any duty cycle isn't a good idea.. how many amp would that be? something horrendous..

If you're building a 555 timer already, it's very easy to have it switch a regulated supply to the LED.

Just use a simple linear driver, lm317, then a transistor from the 555 to switch the current from the lm317 to the LEDs.

Lots of info on making a 555 strobing circuit on the web.

 

[Lyndon]

The number of amps is irrelevant: we're talking about a forward biased LED, not reverse. What is important is that the potential failure mode of the LED from this operation is heating. If the die temperature is kept within limits -- and this is controlled by the duty cycle -- the LED will be fine.


Adding an LM317 or other linear regulator just decreases efficiency.

 

[markus_i]

The number of amps is irrelevant: we're talking about a forward biased LED, not reverse. What is important is that the potential failure mode of the LED from this operation is heating. If the die temperature is kept within limits -- and this is controlled by the duty cycle -- the LED will be fine.

Close, but no cigar. The current through the LED is limited by the internal resistance of your power supply - for any duty cycle and/or frequency, it's just that at higher frequency the internal resistance becomes non-linear. From your description (i.e. your contraption is working), I suppose you're using some small transformer supply, wall-wart or something, which has a sufficiently high internal resistance so that it doesn't fry the LED or its bond wires immediately. If you were to add a sufficiently large capacitor (a few thousand uF or so per LED) between the wall wart and LED driver transistor or try to run your strobe from a 12 V car battery, you'd discover that the bond wires are perfectly capable of acting as (non-resettable) fuses....

Bye
Markus

 

[VidPro]

we made a strobe that lights up a whole huge room, using a 555 and a relay, had it so i could adjust the on-time and rate, it was as good as a real strobe. it used a row of 10 X 3W leds Stars on a aluminum bar for heat sinking.
obviously a Mosfet (insted of relay) would have been better.

the 555 we used had a max output of about 200ma, so i used that to drive a relay.
i wasnt really trying to make a strobe, just a pulse charger for li-ion, and connected it TO the array.
the on/off speed of the leds was certannly fast enough for a strobe.

donno what i would have done for a driver thing, they arent designed for pulses like that on the input, and some drivers will Fail outright without a load on the output.
I drove all three , the 555, the relay, and the leds with li-ion battery, and also with a regulated power supply set for voltage control.

 

[VanIsleDSM]

Don't switch the input, switch the output with a mosfet or a transistor...

If I were you I'd use an LM317 for a current regulator and then a 555 to switch a transistor on the LM317 output to control the strobing.

 

[Lyndon]

You haven't refuted anything I said!

Let me repeat: the "horrendous" amount of current (VanIsleDSM's words) doesn't matter. What matters is heat. In your example the bond wires break due to melting, not because of supply current per se. Therefore, if the ON time of the LED is short enough that nothing absorbs a destructive amount of heat, it will not fail. Even a fast-blow fuse still needs to get up to melting temperature.

FWIW, the strobe was originally running from a bench supply with the current limit set to its max 3A. Outdoors (dark) testing was done with a 12V lead-acid battery. It works like a champ!

Close, but no cigar. The current through the LED is limited by the internal resistance of your power supply - for any duty cycle and/or frequency, it's just that at higher frequency the internal resistance becomes non-linear. From your description (i.e. your contraption is working), I suppose you're using some small transformer supply, wall-wart or something, which has a sufficiently high internal resistance so that it doesn't fry the LED or its bond wires immediately. If you were to add a sufficiently large capacitor (a few thousand uF or so per LED) between the wall wart and LED driver transistor or try to run your strobe from a 12 V car battery, you'd discover that the bond wires are perfectly capable of acting as (non-resettable) fuses....

Bye
Markus

 

[VidPro]

lyndon.
While heat is a major issue, no led is "perfect" the dies have areas that will break down sooner than others, and reduce output even when heat is not a factor, i have a theroy on it that goes further.
but an example of that is AC driven leds off a sine wave that is driven below and above spec in the 60cycles , but it not a heat issue.
Over TIME the leds both 5mm and high power , get dimmer and dimmer as parts of the whole fail to output any light. they still operate, but much of the emitting thing no longer puts out light.
from what i have seen AC driven leds are a total waste of leds, even after i lowered them down quite a bit, the spikes still did thier damage.
one set i tested there was never any reverse voltage, because i dioded one side one way and the other the other way (half wave rectification) but the spikes still keeled it.

i am sure Heat at the tiny jump point DOES still exist indeed, and that might be what damages the jump gates, i am just saying that you cant keep spiking it, as they do decline in output. think molecular on a eteched and doped surface

the output of a 555 only goes so high though, so with the right voltage and limitations of the 555 , many SYNCED 555s seem like a GREAT way to make a strobe cheap