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SSPA 50v and 28v Supply

After building the SSPA's and using a verity of Switch-mode supplies to power them and I quickly discovered that the "Server" style supplies that are readable available are not nice to have in the shack.

They are noisy audible and electrically (well most of the ones I tryed were) so I decided to build a purpose built supply. What I ended up with was excellent both audibly and electrically and wasn't that much work to build either.

The supply consists of 6 Menwell 350W units, three 24v and three 28v units picked up from eBay for around $25. These are nice and quite with temperature controlled fans and good noise suppression on both input and output.

They are configured with a 24v and 28v supply in series with the resulting three sets connected in paralleled. The 28v supplies are at the bottom of the series string with the 24v supplies wound down to 22v on top. In this way I can get the 28v and 50v I require for the various SSPA's used in the station.

The Parallel connection at the 28v and 50v points  are connected via schottky diodes to minimize the voltage drop. The supply output is floating and only gets "grounded" at the input connection to each amp.

The supply is switched on and off remotely from each of the 6 possible connected amps. Each amp 28v or 50v output is also switched via a hi current auto relay so any non operational amp is isolated from the supply.

The supply also has a auxiliary 24v supply which is feed to all amp outputs to drive relays and fans.

The inrush mains current to six switch mode supplies could easily take out the mains socket protection at turn on so to protect against this I have taken the 50v supply line to a relay which shorts out a 10 ohm 50w resistor in the phase line of the input once the 50v is reached.

The two digital displays on the front monitor the 28v and 22v supplies and apart from these and the mains switch its a pretty plain box.

This is the circuit and as you can see not much to it but its proven to be a very reliable and quite supply which easily supplies my SSPA's to the 1Kw out level.

Click on any image to see more detail.

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