Hi Howard,
You're right. The first Models of 555/556 was from
the LTspice "Masc." folder. The second attempt
was the transistor realization from LTspice's
/examples/Educational NE555.asc, following
Mike's advise. Behavioral and transistor model gave me
the same (wrong) results for small signal inputs.
I investigated on the website and I found a few different
realization of these subcircuits, but they had the same
problems.
Correctly the problem was with low voltage behavior of
Trigger and Threshold inputs. I tried to make PWM circuitry
which was perfect in simulation in range of 0 to Vcc, but on
the bench the physical realization felt under 1V ov input voltage.
I asked for samples from IC vendors (ST, TI). On both these
imputes behaved differently, they lost linearity under
1V at Vcc=5V.
Regards,
Peter
