Excellent Article on Protecting Two Parallel Strings of LEDs

[PhotonFanatic]

An interesting read for a common problem in the current issue of LED Magazine.

Title:

TECH NOTES: Avoiding thermal runaway when driving multiple LED strings A current mirror and monitor can save a parallel string from failure.

 

[StevelKnievel]

That's a good read. Thanks for the link!

 

[blasterman]

Explains a lot!

Superb - thanks for the link.

 

[Calina]

I started a thread on the same subject yesterday : http://www.candlepowerforums.com/vb/showthread.php?t=222562

Could a moderator please, regroup these two threads.

 

[jason 77]

oops double post........see below

 

[jason 77]

ok so let me see if I get this diagram on that article.....

The transistors labled BD139 look like one is a NPN and one is a PNP? Also am I to assume the 680R means 680 ohms, and 1R5 is 1.5 ohms?

 

[LukeA]

ok so let me see if I get this diagram on that article.....

The transistors labled BD139 look like one is a NPN and one is a PNP? Also am I to assume the 680R means 680 ohms, and 1R5 is 1.5 ohms?

Those all look like NPNs to me.

 

[Wiggle]

ok so let me see if I get this diagram on that article.....

The transistors labled BD139 look like one is a NPN and one is a PNP? Also am I to assume the 680R means 680 ohms, and 1R5 is 1.5 ohms?

They're both NPN, they just mirrored the symbols to keep the areas where the bases connect to those resistors cleaner.

 

[SafetyBob]

I am glad I am surfing this forum.....I am considering making a replacement lighting fixture for a utility room which has 75% of the original flourescent lighting (undercabinet) replaced with Seoul 4100K P4's from Mouser.

I was actually considering for the big fixture paralleling some of the led's. Unless I can get this little circuit together, I may just keep on doing my serial setups as I have been doing for the past year of so replacing broken flourescent fixures around the house.

I am looking into the Archie AC powered LEDs from Seoul for a instant on security light when any of my cameras detect motion around the house.....not that my Panasonic cameras are worthless, it's just in Night view mode you sure do take a hit on shutter speed. You need all the light you can get.

Do any of you routinely parallel your leds in say 2x6 strips?

Bob E.

 

[znomit]

So a pot on Q2 base will let you unbalance the strings. Any reason not to do this?
I'm thinking a bike light with wide and narrow triple/quad optics on separate strings so you can smoothly dial up any beam width.