[sdiy] Signals leaking into the PSU?

[René Schmitz]

On 24.02.2023 12:38, René Schmitz wrote:
> On 24.02.2023 12:16, Neil Johnson via Synth-diy wrote:
>> Hi Scott,
>>
>>> Here's a way to keep a constant current driving a flashing LED using 
>>> a differential pair.  It only takes one extra resistor and 
>>> transistor compared to the standard transistor
>>> I whipped up a page for it:
>>> https://www.bernacomp.com/elec/og2/constant_current_led.html
>> Thanks - an interesting solution.  My only concern would be driving it
>> from 0V to 5V.  At 0V both bases are at the same voltage so the
>> current will split between the two transistors depending on their
>> matching.  If they were both perfectly matched then the current would
>> split equally between the two paths, so the LED would see half of the
>> "on" current.
>
> Lift the base of the other transistor to 2.5V or something.

That should be via voltage divider like on the other base.


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