Hi there,

I have a simple 555 signal generator (circuit attached) that, using a series of adjustable trimmers, I can get an output of a variety of frequencies, e.g. 200Hz, at around 12V.

However, the output waveform (see attached) has a duty cycle of about 60% but I would like this to be adjustable from 30-60%.

Is that doable with some straightforward modification to the circuit?

Thanks

Jules

 

The standard design only gives duty cycles >50% .

This design with "steering diodes" will give a much wider range:



The datasheet that describes that is no longer available from Philips. This link has an archived copy: http://www.sophphx.caltech.edu/Physics_5/Data_sheets/555appnote.pdf

The description begins on page 4.

 

Thanks for that Sam. With that design can I also go above 50% if needed?
Has the design been withdrawn for some reason?

Julian

 

Thanks for that Sam.

Sam?

OK, Verne.

As for range, it is quite stable from approximately 5% to 95% duty cycle.

 

Lol. Sorry I saw the SamR at the bottom of your reply.
I have read the relevant section and it seems straightforward but what diode spec is Ok?
I have plenty of IN4007s so would the be fine?

Jules Verne

 

Those will work.

 

If you would like to control frequency and duty cycle independently you can follow the 555-timer with a monostable multi-vibrator circuit such as 74HC123, CD4098, CD14528 or CD14538.