I'm referring to this video which I saw on youtube. I'm not sure the effectiveness. video 1

In this video, it shows that by increasing the zener diode value from 6.2V to 11.8V (by connecting 6.2V and 5.6V zener diode in series in the video,) the adaptor output will change from 5V to 12V.

I believe that the circuit is based on a ringing choke converter for normal adaptor and that the zener diode (6.2V) is basically used to regulate the auxilliary winding's voltage in order to drive the transistor with constant current source. I found a reference circuit and its operation for similar adaptor in this link. ringing choke converter example


Add information as below:

Image1 in video

Image2 in video

Image3 in video

Image4 in video

Image5 in video

Schematic reference


  1. Is it true that increasing the zener voltage at the auxilliary winding can increase the output? If yes/no, then why?
  2. What make me so curious with this video is, from my understanding, basically the secondary output will based on the transformer turns. Is there any part/information that I am missing?
  • 3
    \$\begingroup\$ Not many people are going to watch the video to answer your question. Please add a picture of the power supply schematics and the zener into your question. \$\endgroup\$
    – Justme
    May 9, 2020 at 17:16
  • \$\begingroup\$ @Justme, I updated my question with image & schematic \$\endgroup\$
    – Lutz Fi
    May 9, 2020 at 18:31
  • \$\begingroup\$ Why don’t you simulate it? \$\endgroup\$
    – winny
    May 10, 2020 at 7:19

1 Answer 1


This is self-oscillating flyback converter.

The transistor will repeatedly conduct and turn off. When it turns off the magnetic field in the core of the transformer will collapse and the output capacitor will be charged via D8. Simultaneously capacitor C3 will charge via D6 to a similar voltage to the output.

Feedback from L2 goes to the base of the transistor to cause the oscillation. It can only oscillate if the base voltage for each cycle goes enough positive to cause the transistor to conduct.

As mentioned earlier D6 charges C3 negatively from L3 with the flyback voltage. When the voltage is equal to the zener voltage the feedback through R3 and C2 will not be enough to cause the base to go positive and oscillation will reduce in amplitude or stop. If a load is placed the output the voltage on C3 will drop and oscillations will increase in amplitude.

It looks like L2 and L3 have the same number of turns so the voltage at the output will be approximately the same as the zener voltage.


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