Hi all,
I'm pretty new to the forum here but have been loving the EEVblog videos for a few years now. Sorry if this is in the wrong place or duplicated, I found quite a few posts on bench power supplies and some big honkers, but nothing on smaller supplies so here it goes!
I'm working on a 2W power supply with a 277Vrms (line-to-neutral) source and a 3.3Vdc output with a max current draw of around 200mA.
Since we have pretty meager requirements, I've been looking at a resistive or capacitive supply similar to the ones discussed in this
Microchip app note. I simulated the rectified resistive supply in LTspice and found out (more from trial and error with load resistors than the equations in the note) that it can't support a load of more than 50mA. I've attached two pictures of my simulation with a 16? load failing the ckt, and a 70? load showing proper operation.
I can follow the math in the note, but am a little confused as to which equations apply to which topologies and how I can find out what the capacity of the supply is.
Can anyone help explain what is the bottle neck in this supply? Is there a way to pull 200mA from a resistive or capacitive supply? If not, what would be the next easiest/cheapest/fastest design?
I haven't found many step down transformers that I could use for a linear supply, but maybe I haven't been searching well enough. I've also started to look into some Flyback and other SMPS designs, but was getting pretty confused and would really like to get a "good enough" design working while I try to learn about a more efficient SMPS design. If anyone has any advice/references for a SMPS, I'd love to hear that as well!
So is there any way to pull 200mA from this type of cheap supply?
Thanks for any help!