[sdiy] Mysterious transistor on one of the ASM-1 VCO versions

[Aaron Lanterman]

On May 2, 2008, at 5:51 AM, Mike wrote:
>
> My personal view is that the transistor has been drawn in to  
> emphasize that
> the LM311 has an open collector output, and is actually meant to be  
> part of
> the IC. Note that it has no component identifier or part number.  
> Taking a
> look at the Nat Semi datasheet: http://www.national.com/ds/LM/ 
> LM311.pdf
> (time for a new acronym: RTFD), shows the LM311 to have an open  
> collector
> output - so an external NPN wired as show could not actually work -  
> the base
> of the NPN would be connected to -15 Volts or  left open circuit  
> depending
> upon the state of the comparator.

Based on all the responses, you're absolutely right.

> One personal peeve about a lot of CAD circuit diagrams is the way  
> they tend
> to favour layout space over clarity. Having the Comparator in line  
> and to
> the right of the integrator and a bit of tidying would show the  
> function and
> signal flow much better.

> With reagard to the stuck oscillator take note of the bit on th ASM 1
> homepage about the drain/source connections of the FET.

It will probably oscillator better once we take out the extra  
mysterious NPN. ;)

- Aaron