Author Topic: Wich Resistors for Red leds LM386  (Read 1455 times)

Offline thib1903

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Wich Resistors for Red leds LM386
« on: July 21, 2009, 12:49:17 PM »
Well, i just want to know which resistors i have to use for moding my psp 2000.
I am using this method :
https://www.acidmods.com/forum/index.php?topic=28601.0

But someone tells me that's those resistors : 191KOHms and 30KOHms were good for Blue and Green leds .He says that with those resistors,my red leds will not react to the sound cause they don't have the same Forward voltage.Here is the leds i am using :
http://www.phenoptix.co.uk/10_Red_SMD_LED_p/smd-red-0603-110.htm.

So, first question :
Which resistors i have to use  with the lm386 ?(If i use 6 reds leds for example.)

And second one :
How many leds can i put with a LM386?.(i guess it's about 6 but i am not sure .)

Thanks a lot for helping ...
I hope you will understand my poor english  :beg: :beg:
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Offline Jumbo

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Re: Wich Resistors for Red leds LM386
« Reply #1 on: July 21, 2009, 02:01:13 PM »
1. The resistance doesnt change for LED color for the LM386. That resistance is going TO the LM386. What you are going to need to resist is the Output from the LM386 so that the LED's Dont fry. You will need a 43 Ohm resistor for that according to the data sheet from Phenoptix. If you cant find a 43 ohm, just find something close to is, it will be fine. Just try to find a higher numbered one.

2. As many as you want. As long as you supply enough volts to power you can have infinity leds.

Anything else just ask :D

Offline thib1903

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Re: Wich Resistors for Red leds LM386
« Reply #2 on: July 21, 2009, 02:43:47 PM »
ok thanks a lot .But i can't find the exactly good resistors valors.You say it's better to choose more(I guess It 's just for the output resistor) ...

i have to choose between : 180 or 220 KOhms for the  191 one
and 27 or 33 for 30 KOhm

1/Which one seem to be the best for you?

Is that true that if i took the small one (180 and 27Kohms),my leds will be more réactives to the sound ?(this is a bad sentence lol)
Concerned the output,i have a 47 Ohms (it will be good .)
but i don't understand how you got this result ??!!...

I explain :
for six red leds :
U=R*I (I = I led1+I led 2 ...)
R=U/I  (U=5-1,8=3.2)
R=3.2/(0.02*6)
R=26,7 Ohms
2/I must be wrong ?

It was my last request ...
« Last Edit: July 21, 2009, 03:00:26 PM by thib1903 »
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Offline Jumbo

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Re: Wich Resistors for Red leds LM386
« Reply #3 on: July 21, 2009, 05:49:46 PM »
Well the LM386 OUTPUTS 5volts. So 5 volts running a 2.4volt led ( it would be best running about 2volts) at 25mA needs a 47ohm resistor.

Im not sure if that will do anything. It might do something but i doubt it changes reactiveness. You could always breadboard test it and see if it does but i dont think it would even show a difference.

Also, If you cant find the right size, You can always double up with like 180k and 10k making 190k, ect.

 

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