LED and wall adapters

[airbrush]

okay thx...yah that helps...but you said the LEDs will still be dim...i want them to be totally off when you turn it down...that is why i thought we got rid of that one resistor? or should the resistor value just be different then?

 

[audioguru]

Whether your LEDs will be completely off when you turn down your pot depends on the spec's of your LEDs. My MV8191 LEDs will be off. Just reduce the value of the 180 ohm resistor a little if they aren't.

If the 180 ohm resistor 's value is too low or shorted, then you must turn up the pot to more than half-way before the LEDs would begin to light. That's what I call a huge dead zone in the pot.

Which 1.7V LEDs did you order? I'll look at the datasheet to see their spec's. :lol:

 

[airbrush]

here is the link to where i'm getting my leds from:
**broken link removed**
i am using the
5mm sea green 4000mcd
5mm orange - 4000mcd
5mm white - 6000mcd

right...i'll play around with the resistor if i have to, try and removed that dead area from being too much.

 

[audioguru]

There aren't any curves on the datasheets for your LEDs so I am just guessing. The LM317 circuits for your Sea Green and White LEDs will be similar to this:

 

[airbrush]

so the resistors values for the 1.7 leds on the previous page are still correct then??

thx again for your help

 

[audioguru]

so the resistors values for the 1.7 leds on the previous page are still correct then??

Yes.

thx again for your help

You're welcome, I'm glad to help. :lol:

 

[airbrush]

well finally getting some time to finish up this project this week....been slowly chipping away at, gathering materials, cutting, building...now its finally time for the guts...the circuits and wiring. Will have it done soon...i'll post up some pics when its all done.

 

[airbrush]

okay...a slight problem...all the LEDS are still on when the pots are turned down....so i need to reduce the value of the 180 resistor for 1.7volt leds and the 910 resistor for the for the 3.3volt leds schematics accordingly??

How much do I need to reduce it?? what do you suggest to try??

The orange LEDs are the only ones that dim totally off with the pot....but turning it up to max, the LED's are no where near as bright as they should be...what should i check on these?? The resistor for the LED in a series of 2 seems to be correct at 390. So does the resistor on the pot that you are saying to change also affect the max brightness of it...as these are the only ones that dim totally off but are not nearly as bright??

 

[audioguru]

okay...a slight problem...all the LEDS are still on when the pots are turned down....so i need to reduce the value of the 180 resistor for 1.7volt leds and the 910 resistor for the for the 3.3volt leds schematics accordingly??

How much do I need to reduce it?? what do you suggest to try??

Did you build both circuits?
When the pots are turned down, measure the voltage of the regulators' outputs and the voltage across each LED.
Then in the 1st circuit, reduce the value of the 180 ohm resistor and in the 2nd circuit, reduce the value of the 910 ohm resistor.

I guess your LEDs are lower than 1.7V and 3.3V, so calculate the values of new resistors using Ohm's Law.

 

[airbrush]

for the 1.7 leds i'm getting 2.77 where you have 2.75 and 1.53 where you have 1.25...i have no idea how to get a mA reading out of my meter..none of the settings i turn it to give me anything close the number you have there :? .

for the 3.3 leds i'm getting 6.02 where you have 6.0 and 4.77 where you have 1.25!?

like i said...the orange ones are the only ones that seem to work correctly..dim totally off and very little play in the pot before they start lighting up...but they dont seem very bright at all... :?

 

[audioguru]

Hi Airbrush,
I goofed on my calculation of the voltage at the ADJ terminals, your measurements were very close to my corrected calculations.
The current readings are determined by Ohm's Law, since you must break a connection to put a current meter in series. A current meter has a voltage drop so its reading would have error anyway.

The 1.7 circuit puts a max of 26.7mA through two 1.7V LEDs. The max continuous current rating for most LEDs is 30mA. So your orange LEDs are operating near their max.

 

[airbrush]

hmm...thats very strange...the orange ones are no where near as bright as the green or white and they are actually rated at a higher brightness than the green LED are :? ...

okay, so onto the next issue then...the green and white remain on all the time...what would you recommend I change the 910 resistor value to??

 

[audioguru]

hmm...thats very strange...the orange ones are no where near as bright as the green or white and they are actually rated at a higher brightness than the green LED are :? ...

How much is their current? Measure the voltage across the 390 ohm resistor and use Ohm's Law.
You never said what is your voltage measurement of the LEDs so we are just guessing that they are 1.7V.

the green and white remain on all the time...what would you recommend I change the 910 resistor value to??

You never said what is your voltage measurement of the LEDs so we are just guessing that they are 3.3V.

 

[airbrush]

the LEDs are 1.7 and 3.3 respectively...that is the specs from where i bought them from...www.lsdiodes.com

orange:
**broken link removed**

green:
**broken link removed**

white:
**broken link removed**

...again..i appreciate your patience and help on this...couldn't have done this project without this forum and the helpful people on it.

 

[audioguru]

Ok, if the green and white LEDs are rated at 3.3V each, then with two in series with a 220 ohm resistor, why do they light with the 6.02V that you measured? The only way to reduce their brightness is to measure their voltage then change the circuit to match.

You can'simply reduce the value of the 910 ohm resistor to dim the LEDs at minimum pot setting, because then their max brightness will also be reduced. The resistance of the 240 ohm resistor also must be reduced but not as much as the reduction of the value of the 910 ohm resistor.

What is the voltage across the orange LEDs' 390 ohm resistor when the circuit's pot is at the brightest? Also, double check and measure the 390 ohm resistance of the resistor.

 

[airbrush]

Ok, if the green and white LEDs are rated at 3.3V each, then with two in series with a 220 ohm resistor, why do they light with the 6.02V that you measured? The only way to reduce their brightness is to measure their voltage then change the circuit to match.

dont know why they light...so how do i measure the LED individual voltage if they are not correct as they were specified?? :?

You can'simply reduce the value of the 910 ohm resistor to dim the LEDs at minimum pot setting, because then their max brightness will also be reduced. The resistance of the 240 ohm resistor also must be reduced but not as much as the reduction of the value of the 910 ohm resistor.

So how do i keep their max brightness and still have then dim totally off...so is that why my orange ones that dim off are not as bright as they could be?? So you're saying that adjusting the 910 will adjust their min so the dim off and then adjusting the 240 will keep their max brightness?

What is the voltage across the orange LEDs' 390 ohm resistor when the circuit's pot is at the brightest? Also, double check and measure the 390 ohm resistance of the resistor.

will check the voltage across the leds 390 tonite...

 

[audioguru]

[quote="airbrush]so how do i measure the LED individual voltage?[/quote]
Turn up the brightness pot to max and measure the voltage across each LED. Also measure the voltage across the resistor that is in series with the LEDs.
Then turn down the brightness pot to min and measure the voltage across each LED. Also measure the voltage across the resistor that is in series with the LEDs. Don't you have two LEDs in series with a resistor?

So how do i keep their max brightness and still have then dim totally off...so is that why my orange ones that dim off are not as bright as they could be?? So you're saying that adjusting the 910 will adjust their min so the dim off and then adjusting the 240 will keep their max brightness?

Yes, but the resistors affect each other. We need to know the actual operating voltage of the LEDs and their series resistor to recalculate the resistors properly.

 

[airbrush]

yup i have 2leds in series with the resistor....I will do as you said tonite and check that and get back to you....thanks again for your help

 

[airbrush]

alright, here's what i have:

orange pot min:
2.77 vout
2.77 at the resistor
1.32 at the LEDs

orange pot max:
11.27 vout
2.78 at the resistor
1.88 at the LEDs


green pot min:
6.02 vout
5.36 at the resistor
2.62 at the LEDs

green pot max:
11.48 vout
6.44 at the resistor
3.18 at the LEDs

 

[audioguru]

The voltages don't add correctly so I don't know what you are measuring.
To calculate the current of the LEDs, we need to know the voltage across the 390 ohm and 220 ohm resistors.