LED choice for mini3
Sep 6, 2009 at 3:12 AM Thread Starter Post #1 of 8

fewjr

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Hello All,
I was wondering if anyone could give me some insight as to how to choose the proper LED for the Mini3. They offer a calculator here, Calculate Resistors for LEDs which looks straight forward, but I am not sure what to put in the three blanks. I mean I want to be sure I understand what I'm doing.

In the parts list for the Mini3 The Mini³ Portable Stereo Headphone Amplifier it states that "the default resistor values work well for LEDs with rated intensity of about 15mcd to 400mcd. If you have LEDs with much higher intensity than that, you should increase the resistances". I believe the LEDs I ordered may be wrong for my application and need to know if I need to order different LEDs.

These are the ones I have-
Power On LED: http://www.mouser.com/catalog/specsheets/83016.pdf Which has a 5.6K ohm (R6) resistor as default on schematic to limit current.

Charge On LED: http://www.mouser.com/catalog/specsheets/83006.pdf
Which has a 10K ohm (R7) resistor as default on schematic to limit current.

Using the calculator do I use 9 volts as my voltage supply? The amp is powered by a 9 volt battery, but on the schematic I see 16 volts in the power supply: The Mini³ Portable Stereo Headphone Amplifier This may well be part of the charging circuit voltage. I am still trying to understand the schemo.

As far as LED forward voltage and LED current for the calculator, I figured I get those values from the specs for the LEDs I have, is that right?

I was hoping someone could help me understand how to choose the right LEDs.

Thanks,
fewjr
 
Sep 8, 2009 at 6:22 AM Post #3 of 8

fewjr

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Is my question too elementary to garner a response? I didn't cut my teeth on electronics and diy, so I am fairly new to this. While I put my questions to the forum, I do try to educate myself elsewhere. So for those that may view this thread, try here: Choosing The Resistor To Use With LEDs

When I input the numbers needed for various LEDs I come up with much lower resistance for the resistor needed for an LED than that is used on the Mini3 at R6 & R7. Can anyone explain why? For instance, the resistor used for R7 for the charge LED is 10K ohms.

If I use this LED : http://www.us.kingbright.com/images/...P7104SRD-F.pdf

I input 9V for source voltage- 1.85 for the diode forward voltage and 280 mA and I come up with 27ohm for my resistor. 27 ohm and 10K ohm is a big difference. Isn't it?
 
Sep 8, 2009 at 7:52 AM Post #4 of 8

MisterX

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Quote:

Is my question too elementary to garner a response?


Maybe it is just posted in the wrong forum section?
Try Mouser part numbers 78-TLHB4400 and 78-TLHR4400.
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Sep 8, 2009 at 9:29 AM Post #5 of 8

fewjr

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Hi MisterX,
I'm sorry if I posted in the wrong board, but the Mini3 is a portable headphone amp. I don't see where else I should have posted.

Those are the LEDs I bought already as I stated with the posted links. The BOM calls for super-bright LEDs, which these are not and it states that the default resistors (R6, R7) will work with LEDs with a rated intensity of about 15mcd to 400mcd. TLHR4400 and TLHB4400 have a luminosity rating of 1.6 mcd and 6.3 mcd repectively and are not super-bright, only standard/diffused. That is why I thought I may have ordered the wrong LEDs.

And I still cannot figure out why the default current limiting resistors have such a high resistance as opposed to what the calculator ( Calculate Resistors for LEDs ) tells me to use.

Thank You for responding
fewjr
 
Sep 8, 2009 at 1:31 PM Post #6 of 8

chesterqw

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if i am not wrong, they choose a high resistance value so that the LED will use as little power as possible. as you want more of the battery's life for the amp instead of lighting up the LED.
for higher brightness LEDs you need less power to get the same intensity.
i wonder if the LED could be 5mm? maybe a bigger hole for the LED.
but they do have way higher brightness level.
 
Sep 8, 2009 at 7:27 PM Post #7 of 8

dnullify

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this would be better placed in the DIY board for future reference.

and i'd go with MisterX's suggested part numbers, or rather, the specs of each part number. I'd use that for a guideline if you wish to seek out your own colors.

I am currently assembling a mini3 with those two, and so far can not see any problems.
 
Sep 9, 2009 at 4:56 AM Post #8 of 8

fewjr

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Thank you guys for your response.

chesterqw
Quote:

if i am not wrong, they choose a high resistance value so that the LED will use as little power as possible. as you want more of the battery's life for the amp instead of lighting up the LED.


That makes plenty of sense to me. The thing that threw me off was that they have that link to a calculator to figure what value resistor to use for the LED chosen, and also that they mention that the default resistors were good for LEDs with ratings of 15 to 400 mcd. I actually ordered the LEDs that MisterX suggests so I guess I'll be okay. I'm still a little confused as to how you would know to use LEDs with less than 15 mcd though.

dnullify
Quote:

this would be better placed in the DIY board for future reference.


Sorry about that. I see it now that you mention it. head-fi has alot off different forums listed on the main page. I went to main forums. I didn't even notice the ones lower down. Thank you for pointing it out. Sorry everyone if I sounded impatient. It was Labor Day weekend.....people are busy.
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