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Step 2Relaxation Oscillator
By defining the frequency in step 1, R1 can be replaced with a potentiometer, RP, with a value of 2R1, and two diodes. This alteration will allow the duty cycle to vary, whilst maintaining a constant frequency.
For the purposes of general PWM of LEDs, there is no need for absolute precision with the frequency. If there is a requirement for precision, then the potentiometer chosen should be as close to, but no more than 2R1, and a compensation resistor equal to R1-RP/2.
An alternate solution is to use two resistors in series with the two diodes, to give a fixed, and pre-defined duty cycle.
For the purposes of general PWM of LEDs, there is no need for absolute precision with the frequency. If there is a requirement for precision, then the potentiometer chosen should be as close to, but no more than 2R1, and a compensation resistor equal to R1-RP/2.
An alternate solution is to use two resistors in series with the two diodes, to give a fixed, and pre-defined duty cycle.
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