K
Kevin Dressel
- Jan 1, 1970
- 0
All:
Based on the feedback I received from you guys (thanks for that!) and after
referencing a few web pages, I created the following circuit (mind you I've
got two of these paralleled across the cap for 10 LEDs total):
470ohm 5 LEDs in series (Specs show 3.6V drop
@ 20mA)
(+)---------+----/\/\/----|>|-|>|-|>|-|>|-|>|--+
| 1/2W 18V Drop |
| |
Transformer 1000U | |
Vin = 10.5V 50V ----- Filter Cap reads |
w/ no load ----- 27-28V w/ no load |
| |
| |
| |
(-) -----------+-------------------------------+
Now, assuming I understood everything correctly up to this point, I should
be getting approx. 21mA current in the LEDs (28V-18V = 10V / 470ohm ~=
21mA), right? So, why is it then that when I check the current across the
LEDs with the multimeter, I read around 42mA (around 22mA across one LED)?
Also, when I light these LEDs up with a 3.6volt power source (three nicad
batteries), they are much brighter than when used in the circuit shown
above. Does anyone know why this would be?
Am I missing a crucial piece of the puzzle here?
Thanks,
Kevin
Based on the feedback I received from you guys (thanks for that!) and after
referencing a few web pages, I created the following circuit (mind you I've
got two of these paralleled across the cap for 10 LEDs total):
470ohm 5 LEDs in series (Specs show 3.6V drop
@ 20mA)
(+)---------+----/\/\/----|>|-|>|-|>|-|>|-|>|--+
| 1/2W 18V Drop |
| |
Transformer 1000U | |
Vin = 10.5V 50V ----- Filter Cap reads |
w/ no load ----- 27-28V w/ no load |
| |
| |
| |
(-) -----------+-------------------------------+
Now, assuming I understood everything correctly up to this point, I should
be getting approx. 21mA current in the LEDs (28V-18V = 10V / 470ohm ~=
21mA), right? So, why is it then that when I check the current across the
LEDs with the multimeter, I read around 42mA (around 22mA across one LED)?
Also, when I light these LEDs up with a 3.6volt power source (three nicad
batteries), they are much brighter than when used in the circuit shown
above. Does anyone know why this would be?
Am I missing a crucial piece of the puzzle here?
Thanks,
Kevin