Generating a negative voltage - charge pump or switchmode?

[Michael Brown]

One of my pet projects requires a power supply that gives both +48 VDC
and -48VDC (from mains), no more than 3A on each rail. After a bit of a
look, it seems that such power supplies are rather rare, especially here in
Australia. Maybe I'm using the wrong search terms, but I can't even find a
*single* supply that puts out both +48V and -48V. However simple +48V
supplies are relatively easy to get hold of. So, my idea was to tack a DC-DC
inverter onto the output of the +48V supply to get the -48V.

Now, this is an area I'm not too familiar with. I've made simple
capacitor-switching charge pumps before, but for ten's of mA, not 3 A. And
I've never done a proper switchmode supply. My question is - for this
situation, which will be easier to get working: a charge pump or a
switchmode inverter? Strict regulation is not an issue - the 48V actually
goes into another DC-DC converter (don't ask ...) which will hopefully fix
any slight discrepancies in the -48V output.

Or, if someone has a link to a +/-48V power supply that you can buy in Oz,
let me know!

 

[Phil Allison]

"Michael Brown"

One of my pet projects requires a power supply that gives both +48 VDC
and -48VDC (from mains), no more than 3A on each rail. After a bit of a
look, it seems that such power supplies are rather rare, especially here
in Australia. Maybe I'm using the wrong search terms, but I can't even
find a *single* supply that puts out both +48V and -48V. However simple
+48V supplies are relatively easy to get hold of. So, my idea was to tack
a DC-DC inverter onto the output of the +48V supply to get the -48V.

Now, this is an area I'm not too familiar with. I've made simple
capacitor-switching charge pumps before, but for ten's of mA, not 3 A. And
I've never done a proper switchmode supply. My question is - for this
situation, which will be easier to get working: a charge pump or a
switchmode inverter? Strict regulation is not an issue - the 48V actually
goes into another DC-DC converter (don't ask ...) which will hopefully fix
any slight discrepancies in the -48V output.

Or, if someone has a link to a +/-48V power supply that you can buy in Oz,
let me know!

** Err - you need to buy two of them.

Then wire one of them with the + to common.



....... Phil

 

[Michael Brown]

"Michael Brown"

One of my pet projects requires a power supply that gives both +48 VDC
and -48VDC (from mains), no more than 3A on each rail. After a bit of a
look, it seems that such power supplies are rather rare, especially here
in Australia. Maybe I'm using the wrong search terms, but I can't even
find a *single* supply that puts out both +48V and -48V. However simple
+48V supplies are relatively easy to get hold of.

[...]

** Err - you need to buy two of them.

Then wire one of them with the + to common.

I thought this made switchmode supplies unhappy? Or is that just an old
wives tale?

 

[Phil Allison]

"Michael Brown"

"Michael Brown"

One of my pet projects requires a power supply that gives both +48 VDC
and -48VDC (from mains), no more than 3A on each rail. After a bit of a
look, it seems that such power supplies are rather rare, especially here
in Australia. Maybe I'm using the wrong search terms, but I can't even
find a *single* supply that puts out both +48V and -48V. However simple
+48V supplies are relatively easy to get hold of.

[...]

** Err - you need to buy two of them.

Then wire one of them with the + to common.

I thought this made switchmode supplies unhappy? Or is that just an old
wives tale?

** Try reversing the phase and neutral on that one - should even things up
a bit.



....... Phil ;-)

 

[Rich Grise]

"Michael Brown"

One of my pet projects requires a power supply that gives both +48 VDC
and -48VDC (from mains), no more than 3A on each rail. After a bit of a
look, it seems that such power supplies are rather rare, especially here
in Australia. Maybe I'm using the wrong search terms, but I can't even
find a *single* supply that puts out both +48V and -48V. However simple
+48V supplies are relatively easy to get hold of.

[...]

** Err - you need to buy two of them.

Then wire one of them with the + to common.

I thought this made switchmode supplies unhappy? Or is that just an old
wives tale?

Trying to run them _in series_, i.e., if he was looking for a plain 96 VDC,
then it probably won't work. But with the center point grounded, each
supply will have its own load, albeit a lot of the time they'll be shared,
but each supply does its own regulation and doesn't have to worry about
the other.

Just be sure that the supplies have an _isolated_ output!

Cheers!
Rich