Creating dual supply from two power supplies

[Wiggle8]

I am creating a Class-D stereo amp and accidentally bought standard 48VDC power supplies (Meanwell 350-48). The board (IRS2092 L15D) actually needs a dual supply. I have two of the NES-350-48. Can I wire the two supplies in series with the center tapped out to ground?

Due to the transformer in the block diagram, the DC output should be isolated from the neutral and ground connection of the AC input. The withstand voltage rating on the output terminals is 500V as well, which is much beyond 96V (48V x 2).

The actual voltage will be lower as I intend to lower the output voltage slightly since I am running a low impedance load. I intend to adjust both supplies closer to 42V each and will confirm both voltages match before connecting and load and re-measure once load has been connected.

If this is a bad idea and I should explore other options please let me know.

 

[BinaryMike]

I'm not aware of any reason why this shouldn't work as planned, but I would like to see it confirmed. I'm planning to do something similar in a tube power amp project before long. One concern in your application is that the slow-start won't time out identically in both units, possibly causing a whomping turn-on thump.

 

[Wiggle8]

The amp modules do have DC protection circuit of that helps.

 

[DF96]

Due to the transformer in the block diagram, the DC output should be isolated from the neutral and ground connection of the AC input.

Isolated from neutral, yes I should certainly hope so.

Isolated from ground? Nothing to do with the transformer at all. You need to check or ask. Some PSUs are isolated or can be set to be isolated. Others are not and cannot. If the outputs can withstand 500V then this probably means that the outputs can be isolated. There may be a link to be removed. As in all matters, consult the datasheet.

 

[Wiggle8]

Datasheet is located here:
http://www.mouser.com/ds/2/260/NES-350-SPEC-806427.pdf

The only ground connection I see is on the input side off the EMI filter. I have also e-mailed the company though.

This other meanwell supply does show the ground connection though:
http://www.meanwell.com/mw_search/RS-15/RS-15-spec.pdf

 

[Wiggle8]

Should I also install reverse biased diodes across each supply? Would 10A rating be fine?

 

[BinaryMike]

Output voltage reversal is unlikely to cause damage in this type of PSU, but protection diodes do no harm. 1A or 3A diodes might be a good choice because diodes generally fail shorted and then you would be alerted to a problem.

 

[Wiggle8]

Thanks I will go ahead and add the diodes then anyway alongside some rail capacitance (ordered 4 x10000 uf, 63V capacitors - 2 per power supply).

 

[Wiggle8]

Manufacturer has confirmed I can wire these supplies as +/-48V as described above

 

[DF96]

Make sure you add any extra capacitance at the amplifier, not right at the PSU output. This helps ensure that
1. the caps might do something useful,
2. the resistance of the wires from PSU to amp+caps helps to dampen any unwanted resonance (most regulated PSUs have a somewhat inductive output impedance so can interact with extra caps in a way which can surprise some people).

 

[Pafi]

The amp modules do have DC protection circuit of that helps.

This is an important topic, and worth to deal with it a little more. DC protection means high DC output voltage for long time is not allowed on output. But from the point of view of PSU the problem can be a small continuous DC current that pumps charge from one PSU to the other. (So called "Supply Pumping".) This is not avoided by DC protection, a small DC output voltage combined with small DC load resistance can cause pumping current.

Fortunately the IRS2092 also have overvoltage protection that will kick in if this pumping rises voltage too much, so I don't expect anything damaging. Just good to know in case you experience strange things... This usually occures only when there is a short on output terminal, or if transformer is used to match speaker impedance.