- Jan 1, 1970
First offâ€¦ Thank you for all of you that are being helpful.
I now understand the points that youâ€™ve made about my original
question. Since then, I have dug into a more active circuit using
LM317 chip in constant current mode.
Here is a picture of the basic circuit off the Internet.
Here is an Internet calculator I used to size the resistor.
Here is a picture of my circuit (while running) and being lit by the bunch of LEDâ€™s.
And here is a close-up of the circuit.
I used calculator above which indicated I need the 56 ohm resistor
to give me an output current of 22.3 ma. With an input of 120.1 VAC,
I measure 107.1 VDC out of the full bridge. I also measured 106.6 VDC
coming out of the LM317 with no load connected. When connecting to
the load of 40 LEDâ€™s, I get a current of 10 ma. I kind of expected
this since the voltage drop over 40 LEDâ€™s is about 140V.
WHOA! You can't use an LM317 with more than 40V.
As I connect fewer and fewer LEDâ€™s the current goes up as expected.
However, I kind of expected the LM317 to start kicking in and keep the
current around 22.3 ma. In the picture above, you can see that at 36
LEDâ€™s, the current was showing near 30 ma.
Can you tell me what Iâ€™m missing? Some key words would be very helpful for me to research.
On the natinnal semiconductor data sheet the 40V limit is at the top of page 4
An example current regulator circuit can de seen on page 18, it's
basicallythe same as yours.
The 40V limit means the voltage difference between your LEDs and the
input should never exceed 40V. regular 110V AC can have DC peaks
up around 170V somewhere so your LED string is constrained to be one
that drops 130V or more else you risk damaging the LM317 and incorrect
don't forget the fuse.