The circuit in #20 will not work and the chip will fail. The chip would fail because DIS and OUT are complimentary outputs. When ever OUT is high, DIS is low, trying to short OUT to ground. Not good. For the hysteretic oscillator, the discharge pin is not used. OUT goes through the pot to THRS and TRIG. DIS is left floating.

As for the duty cycle, it is very difficult to say. The LMC555 datasheet (2002) does not have plots of output voltage vs current. Also, the values in the tables are for two very different output currents. Reading between the lines, my guess is that the two output transistors are well matched at currents below 1 mA, so the symmetry will be within 2%, and probably within 1%. Maybe one of our local 555 fans has run their own tests ... ?


ak

 

Hello,

Did you have a look at the thread I gave in post #3?

The schematic was made by Wendy.

Bertus

 

When a 555s output pin is “high” the discharge pin is “open” not low.

JFTR

 

Hello,

I tried this circuit on the bench and it produced exactly 50% duty cycle independent of frequency.
The sim shows 14vdc supply but I actually used 12vdc supply on the bench. But it does add a transistor to the mix.

 

The two capacitors are completely unrelated. One has no effect on the other.

ak

 

Does the pot have all 3 terminals attached to the circuit? It looks like you dont have a valid pot symbol and its just being used as a resistor with 2 terminals attached. Have you tried the circuit down to 5v?

Hi

Yes...the pot is wired as a variable resistor (all three terminals used) and the symbol is valid for a variable resistor configuration. The circuit works at 5 volts and the test circuit is running at 22 Hz with parts I had in my junk box.

eT

 

Im going to fab the circuit. Your pot didnt look like my ltspice pot symbol.

Yes... it’s a custom potentiometer symbol.
LTspice has a different symbol.

eT

 

You can check this thread -- Potentiometer - LTSpice and the libraries provided by Bordodynov.