Hello again,
ronv:
Yes that's the problem i found too when going to build a hefty power supply of maybe 30 amps output.
The inductor becomes expensive. Maybe the only way around this is to build several smaller units
and use a paralleling scheme to get a higher output.
An air core inductor sounds interesting, but i have to wonder what kind of efficiency we would get
out of it. Lucky the LM2576 works at around 50kHz, so it's not too high. I guess we'd really
have to try it, and that means winding a large coil with heavy wire for say 20 amps out. Number
12 AWG wire for example. Might be lots of turns however. With a core we dont need that many turns
so it works out a little better, but then again we'd have to get a core too then.
Perhaps you have some other ideas too you can add as we try to think of ways to do this without
spending a fortune.
kinarfi:
I am posting my first thoughts on this project of using the LM2576 to drive a PMOS and thus obtain more
output current and still have the nice control of the LM2576 to look forward to. Keep in mind this
is like a preliminary drawing that i am using to illustrate the basic idea, although from your text
you seem to have a good grasp of this already.
Are you saying you tried something like this already? Note that i used an inverter too but the resistors
that load the internal drive transistor would be small enough to draw some significant current, maybe
at least 100ma or more, even 250ma perhaps, im not sure yet. The LM2576 has to think it is working
as usual. If that means connecting a small inductor too then so be it, if that's what it takes.
Alternately we could look for a controller IC and go from there.
I've also looked at inductors in parallel, but for some decent inductance like 100uH it takes quite
a few inductors. To double the current rating of a single 100uH inductor, it takes a total of
four inductors of 100uH to get the same inductance. So if we had four 100uH 5 amp inductors, we could
make ONE single 100uH inductor that had a current rating of 10 amps (that's twice one inductor rating).
That still might get a little expensive. Of course if we had two 200uH inductors at 5 amps we could do
it with two inductors, but they would be more expensive than the 100uH inductors in some cases.
So maybe a parallel setup would be better where we build several smaller units and parallel them. We'd
have to make sure the complete circuit is stable then and solve any problems that might come up with that.
Take a look at this schematic and see if that is what you tried or not. Let me know so we can figure out what to do next.
ronv:
Yes that's the problem i found too when going to build a hefty power supply of maybe 30 amps output.
The inductor becomes expensive. Maybe the only way around this is to build several smaller units
and use a paralleling scheme to get a higher output.
An air core inductor sounds interesting, but i have to wonder what kind of efficiency we would get
out of it. Lucky the LM2576 works at around 50kHz, so it's not too high. I guess we'd really
have to try it, and that means winding a large coil with heavy wire for say 20 amps out. Number
12 AWG wire for example. Might be lots of turns however. With a core we dont need that many turns
so it works out a little better, but then again we'd have to get a core too then.
Perhaps you have some other ideas too you can add as we try to think of ways to do this without
spending a fortune.
kinarfi:
I am posting my first thoughts on this project of using the LM2576 to drive a PMOS and thus obtain more
output current and still have the nice control of the LM2576 to look forward to. Keep in mind this
is like a preliminary drawing that i am using to illustrate the basic idea, although from your text
you seem to have a good grasp of this already.
Are you saying you tried something like this already? Note that i used an inverter too but the resistors
that load the internal drive transistor would be small enough to draw some significant current, maybe
at least 100ma or more, even 250ma perhaps, im not sure yet. The LM2576 has to think it is working
as usual. If that means connecting a small inductor too then so be it, if that's what it takes.
Alternately we could look for a controller IC and go from there.
I've also looked at inductors in parallel, but for some decent inductance like 100uH it takes quite
a few inductors. To double the current rating of a single 100uH inductor, it takes a total of
four inductors of 100uH to get the same inductance. So if we had four 100uH 5 amp inductors, we could
make ONE single 100uH inductor that had a current rating of 10 amps (that's twice one inductor rating).
That still might get a little expensive. Of course if we had two 200uH inductors at 5 amps we could do
it with two inductors, but they would be more expensive than the 100uH inductors in some cases.
So maybe a parallel setup would be better where we build several smaller units and parallel them. We'd
have to make sure the complete circuit is stable then and solve any problems that might come up with that.
Take a look at this schematic and see if that is what you tried or not. Let me know so we can figure out what to do next.
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