E
Ethan
- Jan 1, 1970
- 0
Hello:
I am just staring on a new design for a medical instrument and need to
figure out the power supplies. I am looking for recommendations on
where to start and what the plusses and minuses are for various
topologies and any general comments on what devices/designs are out
there.
It needs to be a universal input, 85Vac-265Vac, and dc output. The
load will vary between 0 and approximately 30W. For now I am thinking
the output voltage should be a loosely regulated 9V since this is a
convenient starting place for all the other supplies I will need. I am
not really concerned with the low voltage, non-isolated supplies since
there are a lot of straight forward dc-dc ICs and I have a lot of
experience with these.
Most of the reference designs I have seen are for fly back converters.
My concern is that since this is a "patient applied device" (in FDA
terms) the transformer needs to provide reinforced insulation between
primary and secondary. Which means the primary and secondary need to
be physically far apart. A fly back converter requires very low
leakage inductance, so the primary and secondary need to be as close
together as possible. These requirements seem contradictory, so a fly
back might be difficult. Does anybody know what it takes to get a fly
back design to work with reinforced insulation?
I am also looking into various resonant converter designs which should
have no trouble with a large leakage inductance. These topologies
are more complicated, and I haven't seen any ICs that are designed
for this kind of thing. On the one hand: I would have a lot more fun
rolling my own circuit, on the other: this is a real product and low
part count needs to be taken seriously if I can get it to work.
Other big concerns are EMC, radiated and conducted emissions
requirements are pretty stringent, and of course all the other volume
production issues of manufacturability, reliability, part sourcing etc.
What do you guys think?
Ethan Petersen
I am just staring on a new design for a medical instrument and need to
figure out the power supplies. I am looking for recommendations on
where to start and what the plusses and minuses are for various
topologies and any general comments on what devices/designs are out
there.
It needs to be a universal input, 85Vac-265Vac, and dc output. The
load will vary between 0 and approximately 30W. For now I am thinking
the output voltage should be a loosely regulated 9V since this is a
convenient starting place for all the other supplies I will need. I am
not really concerned with the low voltage, non-isolated supplies since
there are a lot of straight forward dc-dc ICs and I have a lot of
experience with these.
Most of the reference designs I have seen are for fly back converters.
My concern is that since this is a "patient applied device" (in FDA
terms) the transformer needs to provide reinforced insulation between
primary and secondary. Which means the primary and secondary need to
be physically far apart. A fly back converter requires very low
leakage inductance, so the primary and secondary need to be as close
together as possible. These requirements seem contradictory, so a fly
back might be difficult. Does anybody know what it takes to get a fly
back design to work with reinforced insulation?
I am also looking into various resonant converter designs which should
have no trouble with a large leakage inductance. These topologies
are more complicated, and I haven't seen any ICs that are designed
for this kind of thing. On the one hand: I would have a lot more fun
rolling my own circuit, on the other: this is a real product and low
part count needs to be taken seriously if I can get it to work.
Other big concerns are EMC, radiated and conducted emissions
requirements are pretty stringent, and of course all the other volume
production issues of manufacturability, reliability, part sourcing etc.
What do you guys think?
Ethan Petersen