Hi all,
I've read this article: Schmitt Trigger Oscillators
Can I use HEF40106BT Hex inverting Schmitt trigger instead of CD4093B NAND gates Schmitt-Trigger?
I want to be able to change the duty cycle. The freq. can vary a little in the process. Around 20kHz should be ok for my purpose.
Thanks

 

Use any common Dual-Comparitor-Chip that suits your Voltage and Current needs ..........
Here's an example PWM-Circuit, ( the bottom half of the Schematic ).
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I want to be able to change the duty cycle

Do you want to use a pot adjustment, or voltage control to change the duty-cycle?

 

Hi all,
I've read this article: Schmitt Trigger Oscillators
Can I use HEF40106BT Hex inverting Schmitt trigger instead of CD4093B NAND gates Schmitt-Trigger?
I want to be able to change the duty cycle. The freq. can vary a little in the process. Around 20kHz should be ok for my purpose.
Thanks

A 4093 with one input tied high is identical to a 40106.
A few of things to watch out for:
1) The Vil and Vih levels are not accurately defined, so the frequency is not particularly accurate.
2) They do take current from the supply when the input voltages are not Vcc or Vss (which is all the time for an oscillator)
3) If you make more than one oscillator from an IC, you need to decouple the supply really well or otherwise they will try to synchronise.
If you need accuracy, go for the comparator instead, especially @LowQCab 's choice of the TLC3702 with push-pull outputs.
The more common LM393 will need pull-up resistors.

 

Do you want to use a pot adjustment, or voltage control to change the duty-cycle?

Yes: pot adj and Vin=9V

 

Yes: pot adj and Vin=9V

In which case, your answer is in figure 8 of the article you read.

 

In theory, a 4093 oscillator with one input tied high should take less supply current than one with both inputs tied together.
Has anyone actually tried it?