brightest 5mm leds without a metal heatsink?

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mpteach

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Will an xp-g draw less ma than a xp-e or simply less vf? If its the latter i may just be transfering the heat from the led to the resistor and paying for the privilege. Do they have neutral tinted xp-g?

Assuming the battery doesn't drop excessive voltage and the dimming is noticeable and it can handle 350ma heat wise i'll use a amc7135, and if it can handle more then i'll use a resistor in parallel with the amc7135 for semi-regulation. Amc7135 are very cheap.... and much less complicated than running my 2 300mah lipo packs in series instead of parallel and using a buck driver..heh
 
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TorchBoy

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A resistor in parallel with the AMC7135 will result in the LED getting more current. A diode or two (or maybe a resistor) in series with the Vdd pin of the AMC7135 will mean the thing is operating out of regulation but probably in a well behaved manner. It could be fun figuring out the value of resistor you need. The AMC7135 needs 2.7 V and draws 0.2 mA in regulation.
 
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mpteach

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A resistor in parallel with the AMC7135 will result in the LED getting more current. A diode or two (or maybe a resistor) in series with the Vdd pin of the AMC7135 will mean the thing is operating out of regulation but probably in a well behaved manner. It could be fun figuring out the value of resistor you need. The AMC7135 needs 2.7 V and draws 0.2 mA in regulation.

Would a diode in series with vdd reduce or increase current through the 7135? This is a constant current regulator and not a constant voltage so i wonder if it will have any effect besides increasing the min regulation voltage from 2.7 to 3.3. Has anyone tried it?

I know a resistor in parralel would increase current thats why i said if it could handle more than 350ma id add a resistor for extra current. Only the first 350ma would be regulated and the rest direct drive, but semiregulation is better than no regulation and i know 700ma wont happen lol, if it didnt melt it would exceed my lipo specs. The high discharge lipos couldnt fit this thing.
 
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TorchBoy

TorchBoy

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Would a diode in series with vdd reduce or increase current through the 7135? ... Has anyone tried it?
It couldn't increase the current. If it dropped the voltage on Vdd below the point at which it could stay in regulation then you'd get a reduced current from the AMC7135; they drop out of regulation quite gracefully, not in a sudden death fashion.

I know a resistor in parralel would increase current thats why i said if it could handle more than 350ma id add a resistor for extra current.
OK... but you'd then be getting perhaps 1 watt of heat dissipated inside a small plastic case. Is that a good idea?
 
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mpteach

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It couldn't increase the current. If it dropped the voltage on Vdd below the point at which it could stay in regulation then you'd get a reduced current from the AMC7135; they drop out of regulation quite gracefully, not in a sudden death fashion.


OK... but you'd then be getting perhaps 1 watt of heat dissipated inside a small plastic case. Is that a good idea?

It probably wont handle more than that, i guess if it even handles that, i really dont know what it will handle. Lol yea it might be like holding one of those laptop powerbricks lol.

How is using a resistor to drop the amc1375 out of regulation for lower current better than just a resistor? When the voltage goes to low and the amc1375 drops out of regulation doesnt it go to direct drive?

edit: 4 of these flip keys taped together have nearly the same dimensions as my 45w laptop powerbrick.
 
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TorchBoy

TorchBoy

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It probably wont handle more than that, i guess if it even handles that, i really dont know what it will handle. Lol yea it might be like holding one of those laptop powerbricks lol.
I was thinking it might be more like holding a blob of melting plastic. :eek:

How is using a resistor to drop the amc1375 out of regulation for lower current better than just a resistor? When the voltage goes to low and the amc1375 drops out of regulation doesnt it go to direct drive?
I've never tried using a resistor like that. Hmm... I suppose the benefit would be in having a current ceiling. Yes, I guess it is direct drive, with a gradually reducing overhead.
 
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mpteach

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The inside of those power bricks are lined with copper sheet to spread the heat evenly over the exposed plastic area. Some of them still get almost hot enough to burn you though!

I cant really calculate the thermal resistance so when i get it set up im going to put a thermocouple in there and slowly turn up the current till i reach my maximum safe temperature.

I wish the 7135 was adjustable.

again is there anwhere faster than kai/dx to get the amc7135?Are there any warm xp-g tints yet?
 
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J_C

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I wonder how much current you could safely put through an XP-G if you use a big 12 gauge wire for a power lead to heatsink it. Seems easier/cheaper than the other alternative of using a 4mm copper rod, though I suppose instead of an official "rod" you could just get the largest diameter solid core copper wire you can locate, or for more cost effectiveness twist together several strands of 14 gauge, solder plate the end and cut, lap it to a flat surface... think I may end up trying that some day.

Wouldn't it be nice if they made some XP-G with an integral lens that attempted to focus a lot more?

Anyway, if you start lining the sides with copper sheeting it is likely you cut down on the RF range, but we don't know how much margin there is to play with on current distance vs minimal distance you require of it.
 
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