555 50% duty cycle

That sort of thing would be in all the books about the 555, and I would have thought in the application notes.

A simpler solution for a lot of purposes is to connect pins 2 and 6 together, with the capacitor from there to ground. The feed that junction with a resistor off pin 3. The capacitor will be charging and discharging through the same resistor, and any variation comes from the not quite symmetrical nature of the output of the 555. I seem to recall the original bit about this, I think it was in "Electronics" suggested a pull up resistor on pin

3, but I never fussed with that, and it's been so long. I think somewhere along the way someone suggested a CMOS 555 would result in better operation.

I was always satisfied with it, and after I came across the circuit about when it came out, I always used it when I need a simple oscillator.

Of course, if you really need exactly 50% duty cycle for some very specific purpose, it may not fit the bill. But I suspect the circuit with the diodes has limitations too. The problem comes from wanting it to remain constant, while the frequency changes, so the more you want to change the frequency, the more trouble it would be to keep to the exact 50%. The easiest way if you need exactly 50% over a wide range is to feed an oscillator into a flip-flop, and there you are, albeit at one half the frequency.

Michael

If it has to be 50% duty cycle take a look at the 4047 configured in monostable mode:

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Blow off the 555 and use a 7555.

See figure 1(a) at:

http://datasheets.maxim-ic.com/en/ds/ICM7555-ICM7556.pdf