Discrete Pulse Width Modulator

Discussion in 'The Projects Forum' started by iimagine, Nov 28, 2013.

  1. iimagine

    Thread Starter Active Member

    Dec 20, 2010
    129
    9
    Adding a couple more transistors to my discrete linear generator, we have a discrete PWM [​IMG]

    What can I say? I like discrete stuffs :D
     
    absf and scelesticsiva like this.
  2. scelesticsiva

    New Member

    Nov 29, 2013
    25
    0
    Can u brief on the circuit?
     
  3. iimagine

    Thread Starter Active Member

    Dec 20, 2010
    129
    9
    Sure, although I have developed a more efficient circuit, If you are interested I will post it.

    Here is how it works: Q1-Q4 are used to generate a linear ramp; Q5+Q6 forms an emitter buffer stage; Q7 + Q5 forms a longtail pair and is used as a comparator; Q8 + Q9 is the output stage
     
    scelesticsiva likes this.
  4. wayneh

    Expert

    Sep 9, 2010
    12,112
    3,039
    Where do you actually modulate the pulse width? I see no variable components.
     
  5. scelesticsiva

    New Member

    Nov 29, 2013
    25
    0
    He he he!"""SALUTE & BRAVO""" Thanks btw iimagine:)
     
  6. iimagine

    Thread Starter Active Member

    Dec 20, 2010
    129
    9
    R7/R8 divider. I was too lazy to simulate a variable resistor :D
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,112
    3,039
    It might be nice to show how well it works, i.e. show what range of percent you can obtain. For instance is it 5-95% or full 0-100%. The frequency of operation is also a critical parameter folks need to know.

    If you actually build one and play with it, you should submit it to the completed projects section.
     
  8. iimagine

    Thread Starter Active Member

    Dec 20, 2010
    129
    9
    Here is the updated version with graphs and some info

    I'm planning to build this soon as I have the time and will post it

    Edit: I know for a fact that my linear ramp gen does work, I have built and tested it. So its just a matter of 'tweaking' the comparator
     
    Last edited: Dec 5, 2013
    absf likes this.
  9. iimagine

    Thread Starter Active Member

    Dec 20, 2010
    129
    9
    Well, here are the test results from the latest version breadboarded. Not too clean, needs a little 'tweaking' but worked on the first try! :)

    I used 2n4401/2n4403 for all transistors; R7/R8 voltage divider was replaced with a 500k pot

    Next, I will build a Color Organ using this circuit to drive LEDs :D

    Please, as always, I would really appreciate any comments on what you think of it and any suggestions to further improve it.

    PS: Since it was breadboarded, the freq was not too stable.
     
  10. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,287
    1,254
    Maybe a little hysteresis would stabilize the comparator?
     
    iimagine likes this.
  11. iimagine

    Thread Starter Active Member

    Dec 20, 2010
    129
    9
    Thanks for the suggestion, a little hysteresis would definitely makes it better.
     
  12. RichardO

    Well-Known Member

    May 4, 2013
    1,235
    384
    Just because it is on a breadboard (a solderless one, I suppose) does not make it unstable. I have built many function generator circuits with sine, square and triangle waveforms. Some work as high as 20 MHz and they are stable and predictable.

    Can you post a picture of how your prototype looks looks?
     
  13. RichardO

    Well-Known Member

    May 4, 2013
    1,235
    384

    Good advice. I should have looked at your waveforms before posting the previous comments.

    I would still be interested in pictures of your prototype, though. :)
     
  14. iimagine

    Thread Starter Active Member

    Dec 20, 2010
    129
    9
    I have pics of my prototypes; breadboard and protoboard :)

    How do I upload these pics? they are too large! approx 2meg per pic.

    I was in the middle of constructing it on the protoboard when I got a suggestion from ronv, It was too late to make any changes so I went ahead and completed it, I will post read outs from this protoboard tomorrow, right now it is working good as an LED dimmer :)
     
Loading...