[sdiy] Mind blown -- TL074 saturated outputs different

mark verbos markverbos at gmail.com
Wed Nov 28 22:26:09 CET 2018


http://hem.bredband.net/bersyn/VCO/8p2ch%20VC%20switch_s.pdf <http://hem.bredband.net/bersyn/VCO/8p2ch%20VC%20switch_s.pdf>


There’s a 3 bit flash converter here, done in the style of John Simonton. Uses a TL074


Mark




> On Nov 28, 2018, at 9:50 PM, David G Dixon <dixon at mail.ubc.ca> wrote:
> 
>>> I need three of these
>>> comparators, and their sole function is to act as a 3-bit AD to 
>>> control some digital switches.
>> 
>> But why do you need precise output voltages from the comparators then?
>> 
>> And if you need quad comparators, why not use the good old 
>> LM339 instead of abusing a TL074 for that purpose?
> 
> What I want to do is easier (in principle) with an opamp that swings
> positive and negative.  I'm using the output state of the comparators to
> provide the threshold voltages to the next comparator in the chain.  In this
> way, I can get a reasonably precise 3-bit AD converter.  My input CV is -5V
> to +5V, and the AD switches state every 1.25V (-3.75V, -2.50V, -1.25V,
> 0.00V, +1.25V, +2.50V, +3.75V).  The 2-bit version I used in my 5-channel
> scanner worked perfectly with just divided raw opamp output, but the 3-bit
> version for my 9-channel scanner is a bit more finicky because the levels
> need to be just a bit more precise.
> 
> However, I will get it working this afternoon.
> 
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