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connect a 3 WATT LED to a 6 VOLT 4.5Ah RECHARGEABLE BATTERY through a LED DRIVER (LM 317) CIRCUIT???? Answered

HII ALL ,,,WHAT IS THE CIRCUIT TO CONNECT A "3 WATT LED"  to a 6 volt 4.5Ah rechargeable battery through a LM317 DRIVER CKT??? I USED RESISTORS BUT THEY DISSIPATED MUCH MORE POWER THAN I THOUGHT??

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mpilchfamily
mpilchfamily

8 years ago

What is the forward voltage of the LED?

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sbdash11391
sbdash11391

Answer 8 years ago

3.5v forward drop , and 750 ma current at full brightness....a schema is highly appreciable

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frollard
frollard

Answer 8 years ago

If it has a 3.5 volt forward drop, don't use 6 volts to drive it with a linear regulator. The reason it gets hot is because it has to dissipate almost half (2.5 volts) at 700mA = 1.75 watts, just to regulate current. As always, I recommend either changing your input voltage to something more reasonable, or using a switch mode constant current driver.

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sbdash11391
sbdash11391

Answer 8 years ago

a switch mode current driver may not meet my space requirements so i decide to switch to 12 volts dc

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steveastrouk
steveastrouk

Answer 8 years ago

really ? You can get them onto less than a postage stamp ?

Steve

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sbdash11391
sbdash11391

Answer 8 years ago

but what about the external circuitry to drive a 3watt led....???

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steveastrouk
steveastrouk

Answer 8 years ago

What do you mean ? A switch mode LED driver fits with the led on about the area of a post stamp. And it wastes no energy.

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sbdash11391
sbdash11391

Answer 8 years ago

ow is it..actually you see the cause of all this fuss is that i never had any prior experience regarding any 3 watt led and i thought of giving my spot light a upgrade from halogen bulb to two 3watt leds....any way i am overwhelmed by your concern for us beginners...i never thought anyone would take it to his/her concern to answer my questions....... it is the help from guides like you which inspires us beginners to pursue our goals....thanks a ton....well could you suggest a book on starting electronics step by step

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frollard
frollard

Answer 8 years ago

so, let's reiterate.

You can get for very low price switch-mode power supplies that are VERY small and have variable input voltages. They are designed to limit the current, not the voltage, so the led gets just what it needs. In a flashlight size, the driver has to be very small - replacement flashlight drivers are usually 3-10 dollars, and are very efficient.

For example:
http://dx.com/s/watt+led+driver

Pick a driver that has the correct input voltage (mains 110/220v AC, or DC to match your battery pack). Decide if you want memory flash functions like high medium low, strobe, etc. Get that driver and wire it up. It's much easier than building your own.

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iceng
iceng

Answer 8 years ago

Or what is the current for the LED?

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steveastrouk
steveastrouk

8 years ago

You won't change the dissipation by using a 317, but it might be easier to get rid of.

trimmable current source.JPG
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sbdash11391
sbdash11391

Answer 8 years ago

would a 12v battery do

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steveastrouk
steveastrouk

Answer 8 years ago

Do what ? Burn more energy in your regulator ? Yes.