[sdiy] led driver from negative power rail

[Derek Holzer]

I flipped a few things around, but the results are quite unsatisfactory 
compared with a much simpler NPN driver off the positive rail. Very dim, 
to start with, and it only seems to light up off the rising edge of the 
clock on the Stepped output, rather than indicate the actual voltage 
coming out. Still no response on the Smooth output at all.

Can anyone point me to a better way of doing this? Otherwise, I guess 
I'll have to pull a positive lead out to the panel as well...

My apologies, BTW, to the original author of the drawing, I have been 
informed it was not for public viewing. I'll get it removed ASAP.

D.

On 9/8/10 1:27 AM, David G. Dixon wrote:
>> Looks like the diode (as drawn) across the transistor's base-emitter is
>> the culprit.
>> The intent appears to be to protect the BE junction from reverse
>> voltage, but it is drawn backwards. Reverse the direction and it should
>> work.
>> In your case, that diode is probably conducting just before the
>> transistor has a chance to turn on.
>
> I concur with Oren.  The LED is also drawn upsidedown.
>
>

-- 
::: derek holzer ::: http://macumbista.net :::
---Oblique Strategy # 41:
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