# duty cycle problem

Discussion in 'General Electronics Chat' started by rky, Dec 1, 2009.

1. ### rky Thread Starter New Member

Nov 16, 2009
22
0
hi..........
i have problem to change the duty cycle....
i have i/p of 9 volts square wave of 50% duty cycle....
but i want to change that 50% to 20%-10% duty cycle......
anybody plz help me out....how can i achieve???
thank you
rky

2. ### Wendy Moderator

Mar 24, 2008
21,839
3,051
Lots of different ways, here's one.

3. ### rky Thread Starter New Member

Nov 16, 2009
22
0
but can i get 3Mhz frequency from this circuit of 20% duty cycle.....????
is 555 works on 3Mhz???

4. ### jpanhalt Expert

Jan 18, 2008
7,682
1,887
What other criteria can you tell us that were not in your original question?

Do you have a circuit that is producing the square wave? Can that circuit be modified? Do you need a variable duty cycle, or just anything in the range of 10 to 20%? Etc.

John

5. ### Wendy Moderator

Mar 24, 2008
21,839
3,051
A TLC555 (a CMOS 555 from TI) goes to 2Mhz, I'm not aware of any other 555 chips that go higher. You have one in mind?

You didn't mention 3Mhz on the first post. Little details like that are important.

6. ### rky Thread Starter New Member

Nov 16, 2009
22
0
oh i m sorry.........yes i have 3Mhz frequency of 50% duty cycle.....
so can i make it of 10%-20%.....?????
its not require to have accurate duty cycle of 10% or 20%.....
but roughly it will ok....nd it is not necessary to vary duty cycle...
i want to just keep my frequency at lower on time and higher off time....thats it...

and @john i generated 3Mhz from 4016 nand gate ic.....nd that wont be changed......
thank you

7. ### jpanhalt Expert

Jan 18, 2008
7,682
1,887
Why? You can often adjust the duty cycle of Inverter/NAND-based oscillators quite easily.

John

8. ### rky Thread Starter New Member

Nov 16, 2009
22
0
@ john can i change duty cycle from inverters???
that i dont know...
how???

9. ### jpanhalt Expert

Jan 18, 2008
7,682
1,887
Yes, by controlling the charge/discharge times in an analogous way to what Bill suggested for a 555. Here is just one of several ways to do that:

If you would post your circuit, we might be able to give more definite advice.

John

10. ### rky Thread Starter New Member

Nov 16, 2009
22
0
yes sir i did this......but i got at o/p side variable frequency not variable duty cycle....
i put constant capacitor and potentiometer.....
so what should i do further???
have i to change capacitor value for variable duty cycle??
thank you

Jan 18, 2008
7,682
1,887
12. ### rky Thread Starter New Member

Nov 16, 2009
22
0
the same schematic you posted, i have....
there is capacitor value of 10pf and used potentiometer..and nand gate ic 4093
and you gave me the link but i coudnt find that how to change duty cycle...
thank you

13. ### jpanhalt Expert

Jan 18, 2008
7,682
1,887
We seem to be having a communication problem. Your initial question referred to a fixed frequency and duty cycle oscillator based on a NAND gate. The schematic I posted is not that.

The link I gave does not describe how to adjust duty cycle. It does describe how the oscillator works. That information, comments in this thread by myself and others, and the rough schematic I provided should enable you to see how to adjust the duty cycle.

Without knowing exactly what your design is, I simply cannot give more advice. I will add that the schematic I posted did provide variable duty cycle down to the limits you want.

John