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# How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

## How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

(OP)
Hello!
I have a test board for a maroc3 asic and it must be supplied with +6.5 Volts and 380mAmps AND -7.5Volts and 40mAmps maximum current.
I have two one-channel voltage/power supplies(PS), (+,-, ground) from different manufacturers.
If I connected the two PSs in series, as I have drawn in the attached picture, then connected the positive(Red)of the second PS to the +6.5V input of the board, the negative(Green) of the +7.5V PS to the -7.5V terminal and the wire connecting +(+7.5) to -(+6.5) to the board's ground(Black), would that be correct?
And, if I take the ground from the wire connecting the two, are they still in series or the connection becomes parallel between two voltage supplies?
If it has become parallel, and the 6.5V and 380mA should act as a voltage supply and the 7.5V and 40mA is a current supply , it should be ok, right? because the Voltage of the voltage supply is smaller than the voltage of the current supply and the current of the current supply is smaller that that of the voltage supply.
Please advise me on how to supply this board with both -7.5V and +6.5V using two different PSs: I have seen this done with +12V and -12V but the quantities are identical and, if I have 7.5V and 6.5V , is it still alright or will that cause problems and if so, what might those be?

PS: we will also buy a new power supply with 2 channels; what specifications should that have in order to properly power this board?
Thank you!

### RE: How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

The sketch looks OK in principle although there's plenty scope for it to still not work if you don't pay attention to the details.

The specifcation is impossible to predict - but you need to consider regulation, noise, ripple, surge capacity and numerous other things when making the choice.

### RE: How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

(OP)
In that configuration, are the two power supplies still in series or is it now parallel ?

### RE: How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

Neither, I would say. They are both supplying a load and that load has a Common/Ground/Zero or whatever you prefer to call it.

Of course, if you only look at the two power supplies, they are in series. And that doesn't change if you connect load to them the way you show.

Is it important for you what you call the connection?

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

(OP)
Hello, Skogsgurra !
What it is called is of no importance but how it might behave is (connecting in parallel two voltage supplies of different values) . I am trying to understand and predict what could happen tomorrow when I make this setup.
I will just leave it like that, without load for a few minutes and then connect a simple resistance and watch what happens to the current (how much is being drawn).

### RE: How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

OK, I see. But you have nothing to fear if you use the connections shown. But, of course, you must make sure that the outputs of the supplies are floating. Else you will have funny (or not so funny) things happen.

Gunnar Englund
www.gke.org
--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

### RE: How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

Please check your ASIC's specification for power sequencing before trying it out. The timing between the two power supplies is often important.

Benta.

### RE: How to supply voltage to a circuit board that needs +6.5V AND -7.5V ?

(OP)
I would just like to end this topic by saying it worked perfectly, with two power supplies from different manufacturers, by using the connection from the caricature...I mean drawing.

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