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Power unused circuits off: should power grounds be switched?
Power unused circuits off: should power grounds be switched?
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Old 17th November 2019, 04:46 PM   #1
zgtc is offline zgtc  Europe
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Power unused circuits off: should power grounds be switched?
Default Power unused circuits off: should power grounds be switched?

Hi,

The crux
The idea is to use an arduino controlled latching relay board. Main question, before going further choosing relays is... should power grounds be switched, or swithing the positive or negative wire/s is enough?

Background info
I'm designing an arduino controlled preamp. Power will be provided by an isolated DC-DC conversion board (taking power from a 12-24V) to LDO regulated 5V DC and 12V DC. Besides de audio input selector (will be using maxw's board) I want to also be able to power unused circuits off. For instance, if I select audio coming from the NAS, I want to cut the 12V DC power going to the phono amp off, and if I select the phono audio, I want to cut the 5V DC going to the RPi/DAC and the 12V DC power going to the SE buffer after the DAC.

Thank you

EDITS:

1. Power switch as alternative to relays? post 20
2. Very basic drawing of PSU-Arduino-RPi connection post 32
3. NPN transistor driver for P-Channel MOSFET post 36
Attached Images
File Type: png preamp-power.png (31.7 KB, 226 views)

Last edited by zgtc; 22nd November 2019 at 03:39 PM. Reason: additional links
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Old 17th November 2019, 05:27 PM   #2
Ketje is offline Ketje  Belgium
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In many cases the ground is also the reference level for the signal.
If you cut the ground connection to the power, the signal lead(s) will be pulled up by the circuit direction positive power.If that's no problem, go ahead !
Mona
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Old 17th November 2019, 07:21 PM   #3
Mark Tillotson is online now Mark Tillotson
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There might in some circumstances be safety issues switching ground - keeping grounds bonded reliably seems a very desirable aim. Besides most relays are limited to DPDT contacts which is only enough to switch +/- rails. Three or four pole latching relays are probably more difficult to source.
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Old 17th November 2019, 07:54 PM   #4
Vovk Z is offline Vovk Z  Ukraine
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Power unused circuits off: should power grounds be switched?
Usually there is no need to switch ground (it's may be even worse).
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Old 17th November 2019, 08:03 PM   #5
MarcelvdG is offline MarcelvdG  Netherlands
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Switching positive and negative (where applicable) supplies is enough to get things switched off properly. Also switching grounds usually causes more problems than it solves; there might be cases where it helps to prevent ground loops, but it also means that the potential differences between the different circuits can become totally uncontrolled.
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Old 17th November 2019, 08:07 PM   #6
Vovk Z is offline Vovk Z  Ukraine
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Power unused circuits off: should power grounds be switched?
And, if it is small-signal cirquits (preamp, etc) - I'm not sure that there is a need to switch power lines. Usually signal wires are switched only.
We switch off usually only larger power devices, like power amplifier.
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Old 17th November 2019, 09:13 PM   #7
zgtc is offline zgtc  Europe
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Power unused circuits off: should power grounds be switched?
Thank you all
Quote:
Originally Posted by Ketje View Post
In many cases the ground is also the reference level for the signal.
If you cut the ground connection to the power, the signal lead(s) will be pulled up by the circuit direction positive power.If that's no problem, go ahead !
Mona
Sorry Mona, didn't quite understand.

Quote:
Originally Posted by Mark Tillotson View Post
There might in some circumstances be safety issues switching ground - keeping grounds bonded reliably seems a very desirable aim.
My power grounds will actually be isolated due to the isolated DC-DC before the relays board. Another option would be having the relays before the DC-DC conversions, in that case all grounds would be the same.

Quote:
Originally Posted by Mark Tillotson View Post
Besides most relays are limited to DPDT contacts which is only enough to switch +/- rails. Three or four pole latching relays are probably more difficult to source.
Yes, that s another story. They exist but are scarce and more expensive... But, shouldn't it be SPSP to switch 5V, and DPST to switch 12V?

Quote:
Originally Posted by Vovk Z View Post
Usually there is no need to switch ground (it's may be even worse).
Quote:
Originally Posted by MarcelvdG View Post
Switching positive and negative (where applicable) supplies is enough to get things switched off properly.
Cool then. I'll simplify.

Quote:
Originally Posted by MarcelvdG View Post
Also switching grounds usually causes more problems than it solves; there might be cases where it helps to prevent ground loops, but it also means that the potential differences between the different circuits can become totally uncontrolled.
OK. I'm going to use isolated rails, but I suppose that's still possible.

Quote:
Originally Posted by Vovk Z View Post
And, if it is small-signal cirquits (preamp, etc) - I'm not sure that there is a need to switch power lines. Usually signal wires are switched only.
We switch off usually only larger power devices, like power amplifier.
That's a good point, but I'm going to use DC power (avoiding AC mains completely). In this scenario, I think trying to avoid over-dimensioning the initial DC source and also avoid wasted unused power makes sense.

Thank you again everyone.
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Old 18th November 2019, 03:01 AM   #8
Vovk Z is offline Vovk Z  Ukraine
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Power unused circuits off: should power grounds be switched?
Quote:
Originally Posted by zgtc View Post
In this scenario, I think trying to avoid over-dimensioning the initial DC source and also avoid wasted unused power makes sense.
It would be good to calc "power budget". For example, if you use relays - it may be that relays itself consume more than small-signal cirquits tbat you want to switch off.
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Old 18th November 2019, 06:36 AM   #9
zgtc is offline zgtc  Europe
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Power unused circuits off: should power grounds be switched?
Quote:
Originally Posted by Vovk Z View Post
It would be good to calc "power budget". For example, if you use relays - it may be that relays itself consume more than small-signal cirquits tbat you want to switch off.
If Im not mistaken, one of the advantages of latching relays is that they only consume power when switching takes place?
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Old 18th November 2019, 08:27 AM   #10
jackinnj is offline jackinnj  United States
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Power unused circuits off: should power grounds be switched?
Switching ground has different meaning in the US vis a vis ROW --
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