[Solved] Would using the output of a 555 timer to charge/discharge its capacitor work?

FZs Asks: Would using the output of a 555 timer to charge/discharge its capacitor work?


I’m relatively new to electronics and playing around with a 555 timer.

I found that for astable operation, all sources I’ve seen recommends the following design (with different resistor and capacitor values to adjust timing):


I wanted to make the output waveform symmetrical, meaning that it should be high and low for the same amount of time.

With that design, however, the time to charge vs discharge the capacitor will differ. I know that I can adjust this by changing the ratio of the two resistors, but if I use a small resistor as the upper one, it will draw more current in the discharge phase.

At that point, another design came to my mind.

My idea​

My idea is to simply connect the capacitor to the output of the 555 through a resistor and charge or discharge it that way:


As far as I see from that simulation, it works fine and generates a perfectly symmetrical square wave.

The question​

  • Would this design work?
  • If so, why isn’t it widespread and why is the former one “preferred” by tutorials, data sheets and other sources (I couldn’t find my version anywhere)?
  • If it wouldn’t, what issues would it have? Why would it be impossible/impractical/dangerous/problematic to use?

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