Electrical Engineering

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user193661

2:19 AM

If I need to step down 120Vac to 48Vac, do I need a specifically 48V transformer?

The Photon

@user193661 Not if you're going to use a regulator to get a more stable/accurate output voltage.

user193661

I will. How close should I get?

The Photon

@user193661 Linear regulator or switching?

user193661

2:36 AM

Probably switching. The output is 48Vdc

The Photon

@user193661 Then I think the main reason to keep it close to 48 V is for safety certification. If all the voltages on the secondary side of your transformer are less than 48 V (rms?) you will have an easier time with safety rules. But you'll want to do some research on this. 48 V rms should be enough to drive a 48 V buck converter, but I don't have enough experience to tell you the true best circuit, etc.

6 hours later…

Asmyldof

8:46 AM

@NickAlexeev You are right. But there's a little rub in annotating them sensibly

In "Annotate Schematics..." and "Board Level Annotate..." there's a sheet and subsheet order

The best way to get sensible numbering that you can still figure out with a multiple copies of the same sheet design is to change their numbering priority so that first all the unique, first sheets are numbered in both annotation systems, and then clump up the doubles at the end

Say you have a sheet "PreBiased OpAmps" (used 4 times), "Power Supply" (once), "Controller" (once), "Primary Interface" (once), "Secondary Interface" (twice), then my ordering setup would be:

1: Controller
2: Power Supply
3: Primary Interface
4: Secondary Interface1
5: PreBiased OpAmps1
6: PreBiased OpAmps2
7: PreBiased OpAmps3
8: PreBiased OpAmps4
9: Secondary Interface2

Since the opamps will likely take most layouting and layout repetition, it's nice to have them fully consecutive, but the important part there is that you have all sheets once in a first line-up, so that all schematic numbers also directly match a set of board numbers, so that you can lay-out all "1-suffix" rooms and copy those over to the 2, 3, 4 etc. The Essential part, however, is making sure that this orde…

i.e. The schematic numbering order should be as 1,2,3,4,5 in the above.

Because you will at some point do something silly with deleting a component and putting it back in elsewhere, where your numbering gets confused and asks you for help, and then it's 99% easier if you set it up like this to begin with

So if you have a lot of repetition, let it export the rooms to the board (many people on the web moan about rooms and tell you to leave them out!?!?), use them to initially layout and position them. i.e. You can layout one room of a type and then use the copy room operation to copy that layout to all other rooms of the same type.

Then when you are overlapping them or they contain global routing, it may become convenient to delete them and set-up a rule blocking the updater from copying them back, and primitives that fall entirely inside the room will either all be copied, or none. So copying a room with global trace's curves and corners in them on the enabled layers will copy all those curves and corners, whether you want it to or not

Or it will copy no traces at all

@NickAlexeev Also, my appologies for being quick on the flag draw for not an answer today. Though I still think it's a bad idea to answer opening with that, I glanced over too quickly

3 hours later…