# Pulses maths

Discussion in 'General Electronics Chat' started by bobsuper, Oct 7, 2012.

1. ### bobsuper Thread Starter New Member

Mar 14, 2011
12
0
Hi
Say you have a pulse width modulator, for instance the output of a 555 astable, pulse 2.
How would you produce another pulse (pulse 2) that is of duration
Length(pulse2) = length(pulse1) X (control amount)
or = length(pulse1) / (control amount)

Thereby producing a second signal whose pulse width will be a certain fraction of the first signal.
I am sure there is some kind of circuit that produces could perform such a simple task (in theory).

2. ### bobsuper Thread Starter New Member

Mar 14, 2011
12
0
*bump*
anybody can point in some direction?
I've spent hours searching for what I need, but I think I don't have the proper terminology...
"pulse duration" "dividing pulse duration" etc, yields nothing..
someone?

3. ### Wendy Moderator

Mar 24, 2008
20,772
2,540
Pulser's math dealt specifically with AM, which is relatively simple and straightforward. Every side band in a AM signal is seen by the output amplifier. The sidebands are very predictable.

You are mixing apples and oranges. What you are talking about is a form of PWM, but even then the differences are interesting.

Consider this though, you are modulating a square wave, which is most definitely not RF, nor is it suitable to broadcast the same. I suspect it takes some high level Fourier Analysis to define all the frequencies that are present, each and every one is handled by the amp. However, it can be shortcutted to a large degree. A perfect square wave is 50% of the total p-p delivered to the load.

Then there is the DC component delivered to the load. This is a form of PWM, remember? It is possible to block the high frequency component and still have power delivered to our load, with is what a classic Class D amplifier does.

Here is an article I wrote on PWM for the AAC book...

Pulse Width Modulation

Mixing analog (as in RF) and digital concepts is usually a mistake.

I cover PWM from a different angle in this article...

LEDs, 555s, Flashers, and Light Chasers , Chapter 5 , The 555 and PWM

4. ### Ron H AAC Fanatic!

Apr 14, 2005
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I think you are barking up the wrong tree, Bill.
What does this refer to?

5. ### Ron H AAC Fanatic!

Apr 14, 2005
7,050
657
I posted a solution in the other thread on the same topic.

Mar 24, 2008
20,772
2,540