[sdiy] PhotoFETs in Lowpass Gates [was: Photodarlington Optocouplers]

[Aaron Lanterman]

On Apr 19, 2010, at 6:49 PM, Tim Parkhurst wrote:

> On Mon, Apr 19, 2010 at 2:55 PM, Aaron Lanterman <lanterma at ece.gatech.edu> wrote:
>> I'm wondering if these weird little things could be put to synthy use?
>> 
>> http://www.datasheetcatalog.org/datasheet/fairchild/TIL113.pdf
> 
> My guess would be that the Fairchild H11F3 would still be a better option. Still shown as In Production, and the data sheet even shows a few nifty analog applications:
> http://www.fairchildsemi.com/pf/H1/H11F3M.html

Ah, well, actually, I ran across the Photodarlington stuff accidentally while searching for info on the H11F3. ;)

One of my students is going to try building a Buchla lowpass gate using H11F3s instead of the vactrols for his class project. From looking at the datasheets it seems that the resistance of the H11F3 is about 10% that of the vactrol for an equivalent LED drive current so I suggested multiplying the main filter caps by a factor of 10 (or whatever the closest easily findable value is). I think this should keep the Q the same.

- Aaron