So I know that LEDs need constant current drivers and it can be done with very simple circuit.
Now, lets say I want to power 10 LEDs in Parallel (???) and I want to use only one driver for all of them. So, 10 LEDs at 100mA each gives a constant current drive of 1A.
I hook them up and all of them turn on... YAY!
So now if ones of the LED burns, the 1A gets pushed through the other 9 LEDs and they can burn as well.
So a chain reaction occurs and I lose all LEDs!
Is there a circuit that allows for burned LEDs and safe keeps the other ones?
The only circuit that protects the leds is one that includes individual resistors for each led.
You can parallel as many resistor-led pairs as you like, but each one must consist of one resistor and one led in series . The parallel strings of resistor-leds are not vulnerable to chain reaction because each has it's own current limiting resistor.
Also, your statement:
So I know that LEDs need constant current drivers and it can be done with very simple circuit.
is not necessarily true. High-power LEDS do so for a led that draws 100 mA, if the operating voltage were 12V for example, and the forward current for that type of led was 100 mA @ 3.0 V
then 12V -3V = 9V/0.01 A = 90 ohms. (nearest standard value = 91 ohms
PR=0.1 A * 9V = 0.9 W (approx 1 W)
Current limiting resistor = 91 ohms, 1W
You need one of these in series with each led.
It's not good practice, generally speaking, but honestly, I think you can get away with putting the 10 LEDs in parallel (provided they're all identical leds), with one 1A constant current source like you originally planned. If one fails, putting 10% more current through the remaining LEDs will not trash them (unlike putting say, 10% higher voltage across them would) unless you're already driving the leds so hard that you don't even have 10% headroom - also, LEDs have a very long lifetime, so unlike a burned out bulb, a burned out LED is not a common problem.
LED arrays in which multiple identical LED dies or series strings thereof are connected in parallel are widely available commercially.
If the LEDs are not all the same, you definitely need separate current limiting for each one, since it relies on the I-V curve being similar.
DrAzzy:
It's not good practice, generally speaking, but honestly, I think you can get away with putting the 10 LEDs in parallel (provided they're all identical LEDs), with one 1A constant current source like you originally planned.
Oooh! You just wait until Mike reads this! We’ll never hear the end of it!
FardinB:
This is a good solution, but what I am working on, I cannot afford wasted energy due to resistance...
Then you are entirely confused, as you previously said:
FardinB:
So I know that LEDs need constant current drivers and it can be done with very simple circuit.
The "simple" circuit is either a resistor, or this one:
It controls the current by "wasting energy due to resistance" - that is precisely how it works.
Your only other option is to use a switchmode current driver - which is definitely not what I would call a "very simple circuit".
As already pointed out, there really is no way to bypass Ohm's Law. If the power supply
is fixed, the only way to make the current "constant" is to add resistance in series with the led. The fact that a transistor is used and the current maximum is controlled by the base current, doesn't make it any less resistive.
I wonder if the OP wants a solution for a problem.
There are ofcourse boost/step-up constant current LED drivers.
So you can have all your LEDs in series, and drive them efficiently.
Leo..
I have a bunch of those flat LED downlights in my house.
The 12watt ones use five LEDs in parallel. 12 strings x 5 LEDs = 60 LEDs per fitting.
I suppose if you keep the same LEDs at the same temperature on the same heasink, you shouldn't worry too much.
Leo..