PWM pulses and polish

Discussion in 'General Electronics Chat' started by kukata, Feb 10, 2011.

  1. kukata

    Thread Starter New Member

    Dec 24, 2008
    Hello everybody,I try to make PWM controled leds with patch pulses and after every repeat they are smalller smaller and off.I hope to understand me,(like 0% -100%-0%,second 0%-80%-0%,third 0%-70%....etc >brightness control),i already have PIC software but the programmer is programed freq to 90 HZ and i see blinking between every step down I controlled led with transistor .I polish this blinking with big capacitor 1000uF paralell on led -i have looklike sine wave from PWM pulses .everiting is ok.But i think this with big capacitor is not good idea.It's too big.and chematic is not so inteligence :) I cant create what schematic to use ,to control led and polish pulses brom base of the transistor maybe.or other.I dont have idea what to try.Maybe sombody will have better answer?
    p.s Soory for difficult explonation and bad EN.
  2. SgtWookie


    Jul 17, 2007
    Hello Kukata,

    The first things that we will need is:
    1) A schematic diagram of your circuit.
    2) The source code for the program that you are using; preferably attached as a .txt file.

    Increasing the PWM frequency to higher than 150Hz or so should take care of the flickering problem.

    Adding a large capacitor across the LED(s) is counter-productive, as when the transistor turns on, the capacitor will become fully charged almost instantly.
  3. kukata

    Thread Starter New Member

    Dec 24, 2008
    ok i will draw the cshematic and will upload but for now i can answer with words.
    SHematic is simple ..transistor in switch mode with resistor and LED in series.Capacitor is 1000UF paralell only to led,It's not charged instantly (becouse it's too big and there is resistor 1K series)it's charged in the middle of PWM patch when duty cicle is almost 90% and discharged from LED concumption after already stopped PWM pulses, I try to make this schematic to drive transistor channel more and less ...and use small capacitor only to polish pulses in transistor base where consumption is smaller and capaciotr will be smaller.Can anyone have idea how cshematic will be realized?
  4. Adjuster

    Well-Known Member

    Dec 26, 2010
    If by "polishing" the pulses in the transistor base you mean averaging them, won't this effectively convert the PWM into rather inefficient linear control?

    (Note that "polishing" is not standard English for an electrical averaging operation. The word "smoothing" is preferable. )