18 VAC to 265 VAC Isolated Supply
I would like to develop an 18 VAC to 265 VAC power supply that has isolated ouputs as follows: 22V @ .5A, 5V @ 0.15A, and 15V @ 0.30A. What do you recommend for a part and is there a reference design that I can use as a starting point?
Comments
Your app note DI-152 Design Idea, TinySwitch-III, has a 3W, isolated flyback design. What is so different about the app note design that the voltage range is acceptable in that case?
Thanks, Dave
I am glad that DI-152 gave us a solution to this kind of wide rang input. As I said, it is difficult for the controller to start up at very low input voltage. So we specified normal operation input voltage range in out datasheets and application notes. However, with the help of external supply to the internal controller through BP pin, TinySwitches can work at very low input voltage. Please refer to the description of how the startup circuit works in DI-152. As the startup problem is solved, you can use TNY280 and PI Expert for your design. The selection of the largest TinySwitch is for both thermal consideration and current overshoot at high input voltage due to very small primary inductance.
Your input voltage range of 18Vac to 265Vac is too wide not only for power device especially the controller but also for transformer design. However you may consider the possibility of combining a couple of designs together and switching from one to another according to the input voltage.