Reverse Protection -- PSU in series

[redrabbit]

From a Lambda power blog, about wiring commercial modular linear psu's, in series......(I want to get +20v)

"Connect back-biased diodes across the power supply terminals as shown below."



"Rate these diodes at the same output current as the power supplies.
In the event both power supplies do not turn on at the same time, or if the load becomes a short circuit, then the diodes will protect the power supplies from any applied reverse voltage."

Would these be schottky rectifiers ??
(I also have some 100 nanosecond, fast silicon rectifiers.)

=RR=

[eyoung]

Hola Y'all...

Would you not want to use a diode bridge With snubbers ???

Regards, Elwood

[Bill_P]

The schematic symbol is for a silicon diode, not Schottky. You can use a Schottky diode if you want. To be safe I would select a 60 volt breakdown rating. If the power supply has overcurrent shutdown or foldback limiting the diodes probably would not need heatsinks.

I don't see a need for a snubber and a diode bridge would not be appropriate here. Bridges are almost always silicon and only half the bridge would be needed.

The diodes are for reverse protection, not oring. Oring diodes are used when connecting power supplies in parallel.

[VivaVee]

Originally Posted by redrabbit

Would these be schottky rectifiers ??
(I also have some 100 nanosecond, fast silicon rectifiers.)

=RR=

I would go further than Bill_P and recommend silicon rectifiers only. Typical schottky rectifiers are not as good as silicon rectifiers when it comes to surge currents and their leakage current is higher. Their reason for existing, low forward voltage drop, is a limited advantage in this case.

That said, I don't believe you need them.

The original circuit (before you added the green wire to 0V) requires the diodes because the two SMPS modules are being run in series in order to get +40V from two +20V modules. The diodes are there for the case when the lower SMPS turns on before the upper one and the load is either short circuited in a fault condition or short circuited temporarily by virtue of a big capacitor that some enterprising audiophile has added to the output - the upper SMPS is then reverse biased by 20V. The diode limits this reverse bias to 0.7V until the upper SMPS turns on and then you get the full +40V as required.

So linking the centre rail to 0V makes the diodes redundant.

They won't do any harm if you do fit them. But you would be advised to fit them to the power input of you audio amp/circuit in case you inadvertently wire the power supply wiring the wrong way.

It pretty much depends on what order you wire everything up as to whether the diodes will do you any good.