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Electronics => Projects, Designs, and Technical Stuff => Topic started by: electros6 on September 04, 2014, 02:41:03 pm

Title: uc3844 flyback converter startup problem
Post by: electros6 on September 04, 2014, 02:41:03 pm

Hi guys,
         I designed a flyback converter using uc3844. when I power up the circuit , the voltage at the Vcc pin swings between the threshold ie approximately between 12 and 16V like a sawtooth waveform. I increase the startup current by reducing the startup resister but result in same. Can somebody figure out the problem
  attached the schematics herewith
       
   

Title: Re: uc3844 flyback converter startup problem
Post by: bktemp on September 04, 2014, 03:12:33 pm

Your feedback winding does not produce enough voltage for the uc3844 to keep running. So it stops until the startup resistor recharges the capacitor.

Title: Re: uc3844 flyback converter startup problem
Post by: T3sl4co1l on September 04, 2014, 03:27:21 pm

Are you actually running it from 48V, and using the winding schedule specified for the transformer?

Title: Re: uc3844 flyback converter startup problem
Post by: electros6 on September 04, 2014, 04:04:42 pm

No, I actually used my own designed transformer for 48V . not the one specified in the datasheet