XPG R5 with no driver?
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znomit
Enlightened
Re: is an XPG with no driver ok?
Yes, you need a driver. LM317 is a good place to start but even a resistor will do.
Yes, you need a driver. LM317 is a good place to start but even a resistor will do.
Re: is an XPG with no driver ok?
Does this make sense:
If I have a 5v supply
And want it to be bright
so might want 1000ma
so for 3.3 vfwd
a 1.7 ohm resistor at about 2watts?
Is there any benefit to using a driver, over a resistor, beside heat/efficiency?
Does this make sense:
If I have a 5v supply
And want it to be bright
so might want 1000ma
so for 3.3 vfwd
a 1.7 ohm resistor at about 2watts?
Is there any benefit to using a driver, over a resistor, beside heat/efficiency?
Fichtenelch
Enlightened
The resistor depends on the current and the current depens on the light you want and the heatsink.
So, assuming..we have 9V and Vf...lets assume Vf with 3.7V.. so, the difference of 5.3V is what we want to get rid of.
R=U/I = 5.3/0.35 = 15,14 Ohm (350 mA drive current)
R=U/I = 5.3/1 = 5.3 Ohm (1A drive current)
could someone please correct me if i'm wrong
So, assuming..we have 9V and Vf...lets assume Vf with 3.7V.. so, the difference of 5.3V is what we want to get rid of.
R=U/I = 5.3/0.35 = 15,14 Ohm (350 mA drive current)
R=U/I = 5.3/1 = 5.3 Ohm (1A drive current)
could someone please correct me if i'm wrong
As I understand for 1000ma in your calcs I'd need a 6 watt resistor which is a problem. Maybe better to use a 5v supply.
Then:
5v
3.3 vfwd for a cree at 1000ma (I think - please correct me!)
1.7ohm
2watt resistor
Is there any benefit to using a driver, over a resistor, beside heat/efficiency?
Then:
5v
3.3 vfwd for a cree at 1000ma (I think - please correct me!)
1.7ohm
2watt resistor
Is there any benefit to using a driver, over a resistor, beside heat/efficiency?
Re: is an XPG with no driver ok?
some of it depends on the wallwart current output. If you have a 9v wallwart that only puts out 100ma it may struggle to drive the LED and burn up when the LED wants too much current from it while a wallwart putting out 500ma may drive it well at 700ma or more and a wallwart capable of 1000mah at 9v may fry the LED.
some of it depends on the wallwart current output. If you have a 9v wallwart that only puts out 100ma it may struggle to drive the LED and burn up when the LED wants too much current from it while a wallwart putting out 500ma may drive it well at 700ma or more and a wallwart capable of 1000mah at 9v may fry the LED.
Re: is an XPG with no driver ok?
depends on the driver, if it has a DC/DC convertor in it then it would be more efficient at converting even able to output more current than put into it by converting the excess voltage into current. some regulators are just smart resistors which regulate things at set limits so output is more stable. a resistor will start out bright and fade till it is all gone.
depends on the driver, if it has a DC/DC convertor in it then it would be more efficient at converting even able to output more current than put into it by converting the excess voltage into current. some regulators are just smart resistors which regulate things at set limits so output is more stable. a resistor will start out bright and fade till it is all gone.
DM51
Flashaholic
Re: is an XPG with no driver ok?
So if I have a 5 volts power supply that sources 4000ma - say from a computer, but I have a resistor, doesn't that resistor limit to *1000ma* and thus prevent the LED from burning up?
So if I have a 5 volts power supply that sources 4000ma - say from a computer, but I have a resistor, doesn't that resistor limit to *1000ma* and thus prevent the LED from burning up?
Re: is an XPG with no driver ok?
resistors are more suitable to drop voltage which limits current. If you have a 5 volt source at enough output to power what you need currentwise then you will need to just figure out the correct resistor size to drop the voltage down to the proper voltage needed to drive the LED at that current level, and the proper size of the resistor to dissipate the power that is lost. If the LED requires 4v to run at 1amp a resistor would have to drop 1 volt and would have 1 amp across it so would need to be a 1 watt resistor (watts law P=IE). At these types of higher current levels I recommend a driver instead but the proper resistor would work just fine.
