Announcement

Collapse
No announcement yet.

Power supply noisy with aggressive PWM

Collapse
X
 
  • Filter
  • Time
  • Show
Clear All
new posts

    Power supply noisy with aggressive PWM

    Hello,

    I was reading an article ... or a blog or something about a student and his professor who designed a power supply that would over drive an LED with a .005 duty cycle ... it basically turned it on for .5 µs out of every 100µs which I initially thought there is no way they would get any light from it because that breaks out to like having the LED on for something like 5 seconds out of every 5 minutes I think ...

    But I guess the point is when you want more light from an LED and you drive it hard for very short bursts of time, you can exceed their rated current levels without burning them out... so I decided to try this with those cheap 3.2 volt 150ma LEDs ... the ones where you can buy 100 of them for $7 on Amazon...

    Anyway, I used a 540N MOSFET with an LED array that I already had soldered up to one of my project circuit boards which normally can run continuously with 19 volts on it, but I decided to crank up the power supply to 30 volts and pulse it with an Arduino.

    The Arduino can't pulse faster than 1µs because the only command that I am aware of for fast pausing is the delayMicro command and you have to write directly to the register ports to skip all the wasted time when using the digitalWrite command...

    So I initially set it up where it would pulse the LEDs for 1µs then 99µs off just to see if I would even get any light ... which surprisingly, I did though it was VERY faint and in a bright room would be almost unnoticeable ... so I cranked up my pulse times to 2µs then 3, etc till I was up to about 40µs on and 60µs off ... but this is where I get to my question...

    As I began to decrease the frequency of my pulses, my bench power supply would just get louder and louder and I'm wondering if that means it's a crappy power supply or even if I'm potentially stressing it out too much or whats the deal with that? I've never heard it make any noise before really so it was kind of strange to hear it in the first place.

    #2
    Re: Power supply noisy with aggressive PWM

    I have to ask are you using a switching power supply to power it if so you might be causing them to fight each other with switching signals just a thought
    9 PC LCD Monitor
    6 LCD Flat Screen TV
    30 Desk Top Switching Power Supply
    10 Battery Charger Switching Power Supply for Power Tool
    6 18v Lithium Battery Power Boards for Tool Battery Packs
    1 XBox 360 Switching Power Supply and M Board
    25 Servo Drives 220/460 3 Phase
    6 De-soldering Station Switching Power Supply 1 Power Supply
    1 Dell Mother Board
    15 Computer Power Supply
    1 HP Printer Supply & Control Board * lighting finished it *


    These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

    1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
    2 Hem Saw Computer Stack Board

    All of these had CAPs POOF
    All of the mosfet that are taken out by bad caps

    Comment


      #3
      Re: Power supply noisy with aggressive PWM

      it's an unsmoothed bench psu - they cant use heavy smoothing or they cant track the current fast enough.

      and it's an unstable lload.

      put a decent size smoothing cap across the input to your circuit.

      Comment


        #4
        Re: Power supply noisy with aggressive PWM

        Originally posted by sam_sam_sam View Post
        I have to ask are you using a switching power supply to power it if so you might be causing them to fight each other with switching signals just a thought
        Yes, it is a switching power supply - This one here

        Originally posted by stj View Post
        put a decent size smoothing cap across the input to your circuit.
        That's a good idea... I'll try that.

        Comment


          #5
          Re: Power supply noisy with aggressive PWM

          Originally posted by EasyGoing1 View Post
          That's a good idea... I'll try that.
          I would start with a low value UF capacitor and work my way up in value until I get the results that you are looking for
          9 PC LCD Monitor
          6 LCD Flat Screen TV
          30 Desk Top Switching Power Supply
          10 Battery Charger Switching Power Supply for Power Tool
          6 18v Lithium Battery Power Boards for Tool Battery Packs
          1 XBox 360 Switching Power Supply and M Board
          25 Servo Drives 220/460 3 Phase
          6 De-soldering Station Switching Power Supply 1 Power Supply
          1 Dell Mother Board
          15 Computer Power Supply
          1 HP Printer Supply & Control Board * lighting finished it *


          These two repairs where found with a ESR meter...> Temp at 50*F then at 90*F the ESR reading more than 10%

          1 Over Head Crane Current Sensing Board ( VFD Failure Five Years Later )
          2 Hem Saw Computer Stack Board

          All of these had CAPs POOF
          All of the mosfet that are taken out by bad caps

          Comment


            #6
            Re: Power supply noisy with aggressive PWM

            Originally posted by sam_sam_sam View Post
            I would start with a low value UF capacitor and work my way up in value until I get the results that you are looking for
            Aren't caps like the state of Texas? Go big or go home? ☺

            Comment


              #7
              Re: Power supply noisy with aggressive PWM

              not in this economy

              Comment

              Working...
              X