True Or False?
1. LED's are current controlled, not voltage? True or False
2. Regulators have a Maxium Limit they can supply before thermal regulation steps in...? True or False?
If (Answer1==TRUE & Answer2==TRUE)
//LED is safe.....
is that Logic incorrect? I know my cheap switching reg's can supply 15 - 30 watt (if heatsink is adequate) .. how
will a 100watt ever "dim" from a max of a 30watt power supply?....
I'm trying to explain why in some, yes SOME instances, it's safe not to use a resistor... providing you have perfect
regulation of voltage with no deviation whats ever from heat or otherwise.http://www.candlepowerforums.com/vb/showthread.php?284177-Direct-Drive
You'll find plenty of Lithium DD flashlights/torches on the market, they don't dim after 2 days lol, point is, anyone who claims "EVERY LED" need's some kind of current limiting device eg a Resistor or
Current Limiter (via a Semiconductor) is wrong, people in the flashlight world do it all the time, providing you don't supply > 4.2v (if it's possible, then sure add a limiter) on some LED.
Be 1 lumen from a 5mm LED or 50,000 from a monster sized emitter of LED arrays, as long as they don't go over that magical voltage number, I don't see the point of an LED on HIGH POWER LED's
if your LED requires a max of 50ma and anything over will kill it, yes give it a 300ohm resistor, protect it, but if your LED requies 100watts, and your power supply can only dish out 50watts at MAX.
Let's say we had a CV of 12v out (15v in via the Regulator) (30watt supply MAX before thermal shutdown kicks in)
12v in +(3.8v LED)- GND
Dead, if it were a 5mm LED.
BUT, after all, LED's are "Current Controlled"
In this instance, let's use a 3.8v LED that supplies an array of LED's but each LED can handle 5amps easy, the entire array let's assumes 100watts of energy.
it sees 12v, it does the same as the little 5mm, it tries to take as much current as possible... the Regulator does so and provies it's full 50watts
of energy to the LED.
Now, we have the LED running at half it's power, it's not dead, it's emitting very brightly and getting very very hot, but we have a nice big 500watt heatsink in the form of a huge finned
heatsink i ripped out from a very old square more heavily armored than a tank and did my back in getting it into the car... so let's now take a look at the regulator.
for argument sake it does manage to supply 50watts and it's not oscillating between low and high power because it's maxed out..
The voltmeter, will show 2-3.8v (since it's 50% capacity, i'd guess the voltage across - and + terminals to be around 50% around 2.8-3.v and a huge voltage drop because it can't supply enough current
as a result the voltage would drop to whatever the LED's is comfortable at emitting at a specific voltage, but sure enough that LED will be alive, unless that Semiconductor peaks > 100watts I really
can't imagine it dying.
but i'd love to see myself proved wrong, on these cheapy regulators, if you show me it going POOF from a really expensive regulator >$100 which supplies > 100watts then fair enough, goahead limit the current
because i would..... I'd also limit the current if i connected it directly to a 12v battery...
I just don't see the need to protect it from something that could never supply enough current to kill it.... take a lithium 4.2v battery, connect a >3watt LED, it should run perfectly fine with no next to no dimming for thousands of hours, LED's fade i'm not against using Resistors, i always do use them always, what i can't accept is people telling me ALL LED's regardless need some kind of current limiting, no not always, if you're careful enough all you need is a voltage controlled regulator and nothing more and be totally safe even with a 5mm LED.
Set 2v via an Adjustable Regulator, connect it in series with an ammeter and adjust until it hits 15-20ma, and stop, read the voltage....
even a 5mm is not going to dim if all you supply is a Precise Voltage, you know the regulator would never produce enough heat to drift off
desired voltage, just how is the LED going to dim without a resistor then?