Bootstrapping old comparators for rail to rail

Projects /  Circuit Ideas  Original post date: 09/18/2017

I actually like the LM393/339 comparators except from time to time I do need the input common mode range to go all the way to Vin like some of the newer parts.  It is pretty critical for low voltage circuits as it eats into your usable input range.

Here is a bootstrap supply that uses a charge pump that runs from a LM393/339 square wave generator.

I played around with the values a bit, but otherwise it is similar to figure 1 from the LM339 (Nation) datasheet back when they have sample circuits.  D1, D2, C1, C2 are the charge pump for boosting the input voltage for running the comparators.

The circuit can drive about 3 extra comparators ( ~190uA each) to 1.5V above Vin=3.3V.  It draws about 3.5mA (RMS)

I haven't tried it, but chances are that it will work first time because I simulated it.