🚀 go-pugleaf

In article <3DC99AD4.2AB0FE52@fanwap.com>,
 "Nucharin W. Jansen" <tong@fanwap.com> wrote:

>Yes, I mean in series.
>But two strings can not use the same R values.
>So sad it very hards to calculate the current and R.
>the forward voltage drop does not identical in each LED.
>and it changes when current change too.
>
>ex:
>
>strings 1 :   ( 12 volt - ( 3.453 + 3.6324 + 3.833 ) ) / 40 ohm = 27 mA
>
>Now I want 20 mA ,  How to calculate the resistor ?
>Since forward voltage change when the current change too.
>

Use a current mirror or current regulator.

Pick up a copy of "The Art of Electronics."  It's what you need.


>
>
>Lizard Blizzard wrote:
>> 
>> Nucharin W. Jansen wrote:
>> > What's happen when voltage drop across LEDs are not same ?
>> > I have problem with white LEDs in series.
>> > I can't control the current.
>> > I have to adjust in real work one by one in each branch.
>> 
>> You say the LEDs are in series, so the current is identical in each one.
>>   All you have to do is put a current limiting resistor in series with
>> those, and use a value that will give you the right current thru all.
>> 
>> If you made a mistake and meant parallel, then yes, you should not
>> connect LEDs in parallel without a resistor in series with each LED to
>> limit and equalize the current.
>> 
>> [snip]
>> 
>> --
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>> 
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