Let's assume that the frequency is 1kHz or period 1ms.What is the pulse period? Unless you know that you can't plot the waveform against an actual time scale.
With PWM frequency >> throb frequency, so in a period of PWM signal, duty cycle can be approximated as a constant but actually it is not a constant at all. So I am wondering what the PWM signal will be if duty cycle is not a constant.I've used this approach to throb an LED. I set the duty cycle of a PWM output to follow a sine wave. It produces a very nice effect.
Of course: PWM frequency >> throb frequency
I don't see a contradiction. A period can have only one duty-cycle, but the 'mark' duration can vary from one period to another.BTW, I think that there is a contradiction here. The duty cycle can be a function of time but it should be constant in a period.
I agree with you about this. However, for the definition of duty cycle function in post #1 or #5, it is a continuous with t and in a switching period the duty cycle is not a constant.I don't see a contradiction. A period can have only one duty-cycle, but the 'mark' duration can vary from one period to another.
This is similar to the instantaneous frequency in a frequency modulated system except that there it is a better defined since everything is continuous and so it make more sense to talk about different frequencies at different points within the same period.I have a square wave where duty cycle is a function of time as below. How can I plot the square wave?
d(t) = 0.5 + 0.1cos(t).
I am confused because at each point in time there is a duty cycle but the definition of duty cycle should be in a period.
That depends on the details of the PWM generator. In my case I was changing the duty cycle setting every tenth of a second or so. Since the throb took several seconds, updating every tenth second gave very smooth operation.How is it possible get a square wave gate drive from that duty cycle d(t)?
This works but then the duty cycle is not actually the one defined above. It is sampled of d(t) and is discontinuous.Here I can imagine a few things. First, imagine that you have not only the rectangular wave output, but a linear ramp that goes from o to 1 over the course of the period. When that ramp first exceeds your d(t) signal that is when your rectangular wave drops from HI to LO. I could also imagine sampling d(t) at the beginning of each period to ensure that each period has one defined duty cycle.
I see how it works in your case because d(t) is discontinuous here.That depends on the details of the PWM generator. In my case I was changing the duty cycle setting every tenth of a second or so. Since the throb took several seconds, updating every tenth second gave very smooth operation.
The PWM would run at a constant duty cycle until the next update. I have no idea how it dealt with a change that arrived during a cycle. It's irrelevant at a practical level, since there were hundreds of full cycles for every one change cycle.
Not really sure what you mean here.To define the pulse width within any period you have to pick an end-of-pulse moment. Do you regard that as continuous or discontinuous?
by Jake Hertz
by Jake Hertz
by Jake Hertz