Switch Mode Power Supply problems

Discussion in 'General Electronics Chat' started by Teemu Laurila, Jun 10, 2016.

  1. Teemu Laurila

    Thread Starter New Member

    Jun 10, 2016
    7
    0
    Hey! I have problems building my own boost converter. It gives around 300V with duty cycle of 50, and if i lower the duty cycle to <10, i can get 5v, thats what i want. The problem is current: I can't get enough current from it. I have code that adjusts the duty cycle if voltage difference is detected. Duty cycle rises up to 60(i don't let it go higher, because overheat), and it gives me around 2V. What i should do? Does parts need upgrade or does that occur from wrong value of inductor? I don't have scope, so i can't really look the behavior of this circuit. I think it might oscillate at wrong frequency or something like that. Arduino code is kinda simple: (yeah, that is only the loop because there is nothing to see in the settings void (except DDRD = 1<<PD2;)

    PORTD = 1<<PD2;
    delayMicroseconds(100);
    PORTD = 0<<PD2;
    delayMicroseconds(100);
     
  2. tsan

    Member

    Sep 6, 2014
    41
    4
    What is the input voltage? Output voltage of boost converter is bigger than input voltage. If you have 2 V at output then input voltage is really small. On the other hand there has been 300 V output voltage too. Do you have always some load on the output? Are you sure that inductor does not saturate?
     
  3. Teemu Laurila

    Thread Starter New Member

    Jun 10, 2016
    7
    0
    In 2.2V, out 190V. If one led with 100 ohm resistor applyed, voltage drops to 3.5v. And that is made with same duty. I have code that changes the duty to keep the 5v, but it still drops below 5v if load is added.
     
  4. tsan

    Member

    Sep 6, 2014
    41
    4
    How you calculated output capacitor size? Just guessing but I think 470 nF is too small.
     
  5. Teemu Laurila

    Thread Starter New Member

    Jun 10, 2016
    7
    0
    i didn't i just picked best i have. I also tried with 2200µF/16V, but the voltage dropped again. That might caused by solderless breadboad :X it is prototype, so i built it to the breadboard.
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    You might want to have a look at the attached PDF.

    Bertus
     
  7. Teemu Laurila

    Thread Starter New Member

    Jun 10, 2016
    7
    0
    I have read that many times, i might need to get deeper to it :p Btw. i like your detail text :)
     
  8. bertus

    Administrator

    Apr 5, 2008
    15,649
    2,348
    Hello,

    In the following PDF there is some extended information.

    Bertus
     
    Teemu Laurila likes this.
  9. Teemu Laurila

    Thread Starter New Member

    Jun 10, 2016
    7
    0
    Ok now thats what i'm looking for! Thanks! :)
     
  10. tsan

    Member

    Sep 6, 2014
    41
    4
    I tried to simulate in LTSpice using 100 ohm load and with 470nF it still works but with 470uF output capacitor there is much less output voltage ripple. Transistor S13003AD has about 0,6 V saturation voltage which is quite much when supply is 2,2 V. On my simulation there was a mosfet and almost no voltage at all across the mosfet. I tested different inductor series resistances. With small resistance operation was ok. If resistance was increased to something like 10 ohms then output voltage started to drop. If you have a small axial inductor it can have quite big series resistance and based on simulation inductor resistance has biggest effect. I also tried 25kHz switching frequency but it didn't make much difference. Otherwise I used 5 kHz as per your code (100us + 100us) switching frequency is 5kHz.
     
  11. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,969
    389
  12. Teemu Laurila

    Thread Starter New Member

    Jun 10, 2016
    7
    0
    I can't trust my multimeter because it's old and uncalibrated, but it shows 12-40 Ohms :X (yeah it's piece of *****)
     
Loading...