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Its neat little circuit you can put inbetween an Oscillator to give you the capability of adjusting its duty cycle!
Here are some key notes about this circuit you should be aware of before you consider throwing it in your own oscillator, or any for that matter:
1. The Output is only designed to be a square wave, if you wish to achieve any other type of output waveform, the circuit will definitely need to be modified.
2. This circuit is currently only designed to be attached to a square wave input, however, it should also just as easily work with a sawtooth, triangular, or sine wave as long as you desire a square wave output, but... if you decide to use as so... you will need to alter the filter attached to the input waveform, (which includes changing the values, or possibly using a slightly different filter). You should alter the filter so that it will handle whatever range of frequencies you plan to use, and so that the filters output oscillates midway of vcc and ground with its Vmin/max being at least 0.75v above ground and below Vcc ( about 1- 2v in general below Vcc and above Gnd should allow for a pretty nice range duty cycles).
3. Make sure the pot is an appropriate size, as well as the resistors bordering its 2 nodes to ensure you are able to effectively adjust the duty cycle.
Troubleshooting:
1. If the Square wave output rounds a little at the top and bottom, or just isn't as flat amd sharp as it should be; then try adjusting the resistor values driving the two transistors at the last stage of the output.
2. If the range of duty cycles is not wide enough, try adjusting the size of the pot, or any of the resistors boarding its 2 nodes. If that doesn't help, try altering the input filter (that could make a huge difference). If neither of those things fix the issue, then verify that the last two transistors driving the output are both fully conducting as they should (BUT NEVER AT THE SAME TIME!!!).
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