Off-line DC/DC Converters

Thread Starter

BlackMelon

Joined Mar 19, 2015
124
Hello,

I am designing an off-line dc/dc converter, or more specifically, a self-oscillating flyback converter to convert a rectified line-to-neutral voltage (220 Vdc) into 15Vdc.
I have read papers from IEEE like those attached among others. However, I have not found a derivation of an equation that I can plug in a high voltage DC input and a DC output to obtain the values of components. Do you have any recommendations of sources?

Thank You
BlackMelon
 

Attachments

ronsimpson

Joined Oct 7, 2019
1,227
I know a self oscillating supply looks simple but it is not simple. It is hard. I have found self oscillating flyback converters to be unpredictable. It is a little hard to get one to work but the real problem is that in production not all will work. My last one, production choose a different vender for a transistor and none worked.

I am hoping to never make another one.
There are many places where you can get the internet computers to design a supply for you if you use their IC.
 

Sensacell

Joined Jun 19, 2012
2,820
Yes- agree 100% with post #2- "simple" circuits are traps for the unwary.
You might get one to work- after lots of fiddling and smoke, then the next one will not work.
 

Ian0

Joined Aug 7, 2020
2,178
Flyback controller ICs are so cheap these days that it will probably cost more to make the self-oscillating type.
IC driven circuits will probably switch more cleanly and thus be more efficient, avoiding costs for heatsinks.
 

Thread Starter

BlackMelon

Joined Mar 19, 2015
124
Flyback controller ICs are so cheap these days that it will probably cost more to make the self-oscillating type.
IC driven circuits will probably switch more cleanly and thus be more efficient, avoiding costs for heatsinks.
Of course, I totally agree with you. The most common IC to my experience is SD6835, a cheap Chinese-made version of the controller IC. However, it is reliable. Unfortunately, some of the power supplies still use discrete components. So, I need to be able to design and fix them, since my work covers both maintenance and designs.


Sensacell and ronsimpson
Your words scared me so much! lol. Anyway, thank you for sharing your experience. I will analyze the converters carefully.

If I have any progress, I will update you guys. ^_^
 

Ian0

Joined Aug 7, 2020
2,178
OnSemi also has a good choice of devices, especially if you prefer the external MOSFET circuit, which does give a bit better flexibility.
 
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