Power Supply Fan-out, what is it?

Discussion in 'General Electronics Chat' started by ElecTech2012, Jan 15, 2013.

1. ElecTech2012 Thread Starter New Member

Jan 15, 2013
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Hello!

I was wondering if I could get a bit of help from the community in regards to a question about power supply fan-out. It is a term I was not familiarized with in trade school a couple years ago when I did my electronics technician course.

And just a note, I'm not referring to an exhaust fan or anything like that.

The question I was given is a two-part one:
1. What is fan-out as it pertains to our power supply?
2. How do we compensate for fan-out?

Now, a brief background on the equipment that said power supplies are on (as much as I know right now, I'm still being trained on this piece of equipment and training has not yet gotten to power supplies). It is on a laser-imaging machine for a newspaper. The power supply outputs are connected to various inputs on an imaging control board to run the various parts of the machine.

There are a total of nine outputs on this supply: +5Vdc, +12Vdc, and a combination +5V and +12V return on the top half. The output terminals are screws with the wires Sta-kon'd with eyed connectors. The bottom half has six outputs: -5Vdc, -5Vdc return, -12Vdc, -12Vdc return (both these returns are separate lines). These run into a plug-in connector on the power supply circuit board.

On the schematic, this one power supply has to supply 28 inputs from the imaging board to power the various parts of the machine. There are only nine outputs available.

Judging from what I know, can I assume that fan-out in the sense of a power supply would work in a similar sense as a TTL: the maximum number of digital inputs that the output of a single logic gate can feed? As such, if there were more inputs that needed to be put onto that output, then a buffer would need to be installed to compensate (in the case of a TTL, a logical inverter)?

So in essence, what I am wondering is if this theory listed above is the same for a power supply, and if it is, what would be the way to compensate for fan-out on a power supply such as this?

Any help would be appreciated, this question has been bugging me for quite some time. Thanks!

Oct 15, 2009
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3. GopherT AAC Fanatic!

Nov 23, 2012
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I am guessing your task master was using the team fan-out to imply, as you assume, the number of boards and devices it can power. The term "fan out" is technically just a number of chips of the same class (e.g. 74LSXX). It does not an amperage load and only accounts for triggering the input pin on the downstream chips, not powering the downstream chip. I guess you will have to check current draw of each device.

4. ScottWang Moderator

Aug 23, 2012
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Power supply is using current as mA or A to represent it, but it isn't means that Fan-out, Fan-out is using in logic as a output of TTL can be sink how many input logics, ex : if one input logic is 1.6mA, and the output of TTL can be sink 16mA, then the TTL of Fan-out is 16mA/1.6mA=10, so that's it, Fan-out just a number.