[sdiy] thanks for replies - Blue LED

[Michael Bacich]

On Oct 22, 2006, at 5:06 PM, harry bissell wrote:

> If you are using 4000 series CMOS and they are in the same  
> package...you can
> parallel inverters.

Yes, now that you mention it, I have seen several instances of CMOS  
inverter outputs being paralleled without any resistors or diodes  
between them.  There are a few old Roland products that had cheap 6  
and 8-bit DACs made from CMOS inverters driving a string of resistors  
in R/2R formation (for instance, the MPU-101, the CSQ-600, and maybe  
even the TB-303).  I think Oberheim also did this in their cute  
little mini-sequencer for the Two-Voice.  These DAC circuits would  
often parallel a few inverters that were driving the lowest values in  
the R/2R ladder, to ensure consistent current drive.  There would  
sometimes be as many as four inverters in parallel. The outputs of  
the paralleled inverters were tied directly together without  
resistors between them.

And yes, 30ma through a blue LED?  Ouch.