AC Regulation of Transformer output

Discussion in 'The Projects Forum' started by Denesius, Feb 28, 2014.

  1. Denesius

    Thread Starter Member

    Feb 5, 2014
    89
    14
    Have a question: the attached (admittedly rough) circuit is a layout for converting 5VDC to 240VAC (60hz, around 40VA full load), +/- 15% on the output voltage. The driver circuit puts out 40% duty cycle square waves to drive each power MOSFET (T1 is a small torroidal transformer, originally 240V primary & 24 VCT secondary, 50VA).
    The problem I've encountered is that with no load, the output of the transformer is around 280VAC, but with full-load saturation I get around 190VAC. I had the idea to rectify the output of T1, use a split resistor network to drop it down & feed it into the feedback line of the switcher, but after burning out 2 chips I realized that either the switcher wasn't seeing the proper feedback & overloading itself, or induced voltage spikes was burning it out.
    I know there are voltage dependent resistors out there, but would they be responsive enough to feedback-adjust the switcher, or is there another clever way to achieve regulation?
     
  2. alfacliff

    Well-Known Member

    Dec 13, 2013
    2,449
    428
    smps feedback is usually opto isolated, to isolate the secondary from the primary dircuits. going from high voltage on the output side to low voltage on the input without isolation can cause a lot of spikes and over voltage conditions.
     
Loading...