How to calculate the duty cycle of this circuit

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WinterInJuly

Joined: 03 Jun 2005
Posts: 68
Helped: 2

06 Jul 2005 5:14 calculate duty cycle

Hi all!
Does anyone know how to calculate the duty cycle of this circuit? the frequency =1/RC
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IanP

Joined: 05 Oct 2004
Posts: 6492
Helped: 1542
Location: West Coast

06 Jul 2005 7:07 how to calculate duty cycle

It needs the same time to charge capacitor 0.22µF through 22MΩ and dischage it through the same way, so the duty cycle is 50%.
Regards,
IanP

Btrend

Joined: 26 Dec 2003
Posts: 424
Helped: 55

06 Jul 2005 8:27 calculating duty cycle

u can run a simulation to get the answer!
anyway, from hand calculation, the duty cycle should be 50%.
and the negative input should charge and discharge with the same rate between 0.12Vdd to 0.88Vdd.

WinterInJuly

Joined: 03 Jun 2005
Posts: 68
Helped: 2

06 Jul 2005 8:38 how to calulate duty cycle

Thanks
How to modify this circuit to change the duty cycle? For example, i want the duty cycle is only 5%
Regards

IanP

Joined: 05 Oct 2004
Posts: 6492
Helped: 1542
Location: West Coast

06 Jul 2005 9:05 how do you calculate the duty cycle

Use an ordinary diode such as 1N4148 and 1MΩ variable resistor.
Connect the diode in series with VR and connect this circuit in parallel to resistor R.
By changing direction of a diode you will be able to adjust high or low ratio
If you use two diodes and VR between them connected in such a way that the middle pin of VR will be connected at one side of R and both diodes at the other end of R you will be able to adjust duty cycle from, say, 5% to 95%.
Regards,
IanP