Switching power supply

Iam working on flyback with 200-500 volt input and 300 volt output with 100watts power out put iam using uc3842 ic, i designed transformer to assure itwont saturate when vlotage is above 400v everyrhing almost work fine ,but under this voltage (output voltage also under desire voltage) it has a strange drain waveform(double pulse to switch for turn on in a very short (1us)time in relative to working frequency (100khz)),i also try to fix compensating with ti aplication note, but no idea i will post images from my oscilloscope, what is problem? Thanks for reply

by Asr36928
March 20, 2021
Add comment...

Please sign in or create an account to comment.


1 Answer

Answer by febb

You probably need to use or tune RC filter required to connect Isense resistor to Isense chip pin to prevent false spikes caused by switching MOSFET. It is described in UC3842 datasheet in details.

+1 vote
by febb
April 10, 2021
Add comment...

Please sign in or create an account to comment.


Your Answer

You must log in or create an account (free!) to answer a question.

Log in Create an account


Go Ad-Free. Activate your CircuitLab membership. No more ads. Save unlimited circuits. Run unlimited simulations.

Search Questions & Answers


Ask a Question

Anyone can ask a question.

Did you already search (see above) to see if a similar question has already been answered? If you can't find the answer, you may ask a question.


About This Site

CircuitLab's Q&A site is a FREE questions and answers forum for electronics and electrical engineering students, hobbyists, and professionals.

We encourage you to use our built-in schematic & simulation software to add more detail to your questions and answers.

Acceptable Questions:

  • Concept or theory questions
  • Practical engineering questions
  • “Homework” questions
  • Software/hardware intersection
  • Best practices
  • Design choices & component selection
  • Troubleshooting

Unacceptable Questions:

  • Non-English language content
  • Non-question discussion
  • Non-electronics questions
  • Vendor-specific topics
  • Pure software questions
  • CircuitLab software support

Please respect that there are both seasoned experts and total newbies here: please be nice, be constructive, and be specific!

About CircuitLab

CircuitLab is an in-browser schematic capture and circuit simulation software tool to help you rapidly design and analyze analog and digital electronics systems.