"Ned Simmons" wrote in message
...
On Tue, 25 Sep 2018 09:15:10 -0400, "Jim Wilkins"
wrote:

"Ned Simmons" wrote in message
. ..
On Mon, 24 Sep 2018 19:30:37 -0700 (PDT), whit3rd

wrote:

On Monday, September 24, 2018 at 6:12:23 PM UTC-7, Ned Simmons
wrote:
On Sat, 22 Sep 2018 19:44:42 -0700 (PDT), whit3rd

wrote:

A constant current source is ideal for powering LEDs; with the
right
size LED (or the right multiplicity of paralleled LEDs) that's
useful power.

Sure, but you can't just connect parallel strings of LED's to a
constant current source and expect the current in the individual
strings will be equal.

Yet, it's done all the time. A 'nine-LED' flashlight with three
AAA cells
has nine strings of one LED each, in parallel.

Desk lamps with three or four LED strings in parallel are common,
also.
Sometimes resistors are added to each string, but not always.

So how do you insure that the current is divided equally among the
strings?

--
Ned Simmons

They are somewhat self-ballasting, as shown by the I-V curves.
https://www.electronics-tutorials.ws/diode/diode_8.html



Unless I'm misintrepeting the curves, or looking in the wrong place,
the graph shows a potential for runaway -- the slope of the curves
increases with increasing voltage.

Here's a similar curve for a tungsten filament, which is
self-ballasting.
https://www.quora.com/What-does-the-...lamp-look-like

This article talks about the hazards of paralleling strings of LEDs.
https://www.ledsmagazine.com/article...-magazine.html

--
Ned Simmons

Try this:
https://www.cree.com/led-components/...LA1BWKWMKW.pdf

The slope isn't straight like a resistor voltage divider, the reason
I qualified them as "somewhat". It also shows their limited tolerance
for reverse bias.

-jsw