Does this look ok to you? (method to activate power supply)

[Smillsey]

Hi all

I have a +48V and a -48V rail in my product.

I want to use the -48V to supply an isolated DC - DC converter - but I am not sure I can…

See the picture

I imagine the enable line on the bottom PSU could cause me an issue here as it will be fed by Logic referenced to GND which in that circuit will be 48V above the -VIN pin

--- Updated Dec 21, 2021 ---

After a little more reading - it seems you leave pin 3 open circuit to turn the PSU on

i might just do that - I don’t really need control of them so might as well just i enable them

 

[KlausST]

Hi,

Every power supply's ENABLE (PIN3) is referenced to it's -VIN (PIN2).
The power supply does not know what your circuit's GND is.

So as long as -VIN is not connected to your circuit's GND you could simply use an optocoupler to ON/OFF the power supply.

Klaus

 

[FvM]

So as long as -VIN is not connected to your circuit's GND you could simply use an optocoupler to ON/OFF the power supply.

Or a discrete transistor level converter.

 

[Smillsey]

Thanks both, I have ended up floating both REMOTE_ON_OFF pins as i want the +12V and -12V to be active all the time.

I can't see any issues with the way in which i am using the -48V supply to power the "PS2" PSU below, can you see any issues?

 

[cupoftea]

no its fine, accords with the datasheet...

https://www.xppower.com/portals/0/pdfs/SF_JCK50.pdf

..and im sure you realise that you need input and output capacitors, and pref some little 100n ceramics right on the pins.

 

[FvM]

I would ask about the characteristic of both rails, current capability and power quality, also if your +/-12 V load has any problems with different power sequences.

 

[Smillsey]

no its fine, accords with the datasheet...
..and im sure you realise that you need input and output capacitors, and pref some little 100n ceramics right on the pins.

Hi cupoftea

Thanks for the feedback.

Do you mean the 220uF they refer to to provide immunity to IEC61000-4-4 and IEC61000-4-5?

I actually was not going to install these as the PSUs are fed by an AC-DC 48V converter which will have it’s own IEC61000 compliance so the ports to the XP POWER supplies are not accessible to the outside world.

--- Updated Dec 22, 2021 ---

I would ask about the characteristic of both rails, current capability and power quality, also if your +/-12 V load has any problems with different power sequences.

Yes I’m pretty happy with that side of things

Most downstream circuits are then fed by low noise LDOs coming off the +/-12V

 

[KlausST]

Hi,

I see no need for a dual 48V input supply. I rather think it´s more easy to supply both from +48V only.

Klaus

 

[Smillsey]

Hi,

I see no need for a dual 48V input supply. I rather think it´s more easy to supply both from +48V only.

Klaus

I know it seems ridiculous , but I need the -48V there for other requirements and I am trying to balance out the power so I still have plenty spare on the +48V rail

 

[cupoftea]

Do you mean the 220uF they refer to to provide immunity to IEC61000-4-4 and IEC61000-4-5?

I actually was not going to install these as the PSUs are fed by an AC-DC 48V converter which will have it’s own IEC61000 compliance so the ports to the XP POWER supplies are not accessible to the outside world.

The JCK50 will need capcaitors at its inputs.....i cant see in the datasheet any details of internal capacitors....so best add some in.....the regulations are one thing...but SMPS's need input and output capacitors to actually work....and they should be near their terminals, not just in the "feeding" power supply.

Once its workign right, then we can think of the regulations, but yes, the standards will be important, and you can use the caps they recomend.

 

[Smillsey]

Do you mean the 220uF they refer to to provide immunity to IEC61000-4-4 and IEC61000-4-5?

I actually was not going to install these as the PSUs are fed by an AC-DC 48V converter which will have it’s own IEC61000 compliance so the ports to the XP POWER supplies are not accessible to the outside world.

The JCK50 will need capcaitors at its inputs.....i cant see in the datasheet any details of internal capacitors....so best add some in.....the regulations are one thing...but SMPS's need input and output capacitors to actually work....and they should be near their terminals, not just in the "feeding" power supply.

Once its workign right, then we can think of the regulations, but yes, the standards will be important, and you can use the caps they recomend.

I’m pretty sure these have input and output caps - I’ve used them in other applications