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5v regulator on positive leg of chipamp PSU
5v regulator on positive leg of chipamp PSU
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Old 31st August 2019, 08:03 PM   #1
mandocaster is offline mandocaster  United States
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Default 5v regulator on positive leg of chipamp PSU

I'm thinking of embedding a raspberry pi in my existing chipamp's enclosure to run RuneAudio.


I want to use a 5v regulator and attach the circuit to the positive output of my chipamp's unregulated power supply.


My question is, with the Pi running at maybe 3A (max), will this extra current being drawn on just the positive rail, cause an imbalance in the +/- power supply, which could cause a DC offset on the output, or have other deleterious effects?


If I have to, I will get a second transformer just for this circuit. I have the room. But it would be cheaper/easier if I could just run it off the existing transformer/rectifier.


Thanks!
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Old 31st August 2019, 09:20 PM   #2
rayma is offline rayma  United States
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It could unbalance the supplies, and/or increase the ripple voltage.
Also that will cause high dissipation in the 5V regulator, unless it is a switching regulator.
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Old 31st August 2019, 09:42 PM   #3
mandocaster is offline mandocaster  United States
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Yeah, it was gonna be a switching regulator. Kinda hard to find linear ones with enough amperage while still not needing more heatsink. The unbalanced supplies are what I was worried about. No biggie, I can throw in a 12v transformer just for the pi.
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Old 31st August 2019, 11:42 PM   #4
benb is offline benb  United States
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5v regulator on positive leg of chipamp PSU
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Originally Posted by mandocaster View Post
Yeah, it was gonna be a switching regulator. Kinda hard to find linear ones with enough amperage while still not needing more heatsink. The unbalanced supplies are what I was worried about. No biggie, I can throw in a 12v transformer just for the pi.
With a switching regulator it will pull proportionately less current from the rail (minus some inefficiency), but still...

Is the power supply (and thus line voltage) also in the same case? I'd get one of those several-amp-output wall-wart supplies they sell for the Pi and wire the plug-in blades to the chipamp supply primary.
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Old 1st September 2019, 07:19 AM   #5
jan.didden is online now jan.didden  Europe
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Would the Pi really draw 3A?? That's excessive. Maybe the 3A is the spec for the brick you currently use to run it?

Jan
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Old 1st September 2019, 07:46 AM   #6
Mooly is offline Mooly  United Kingdom
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5v regulator on positive leg of chipamp PSU
Unbalanced supplies have no real impact on DC offset. -/+20 or -15 and +25 or -25 and +15. All would still give zero volts offset at the chip amp output.
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Old 1st September 2019, 05:42 PM   #7
mandocaster is offline mandocaster  United States
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Would the pi draw 3A? Not by itself. A Pi 3 is rated at 2A max. I'm not sure how much the DAC hat draws, and I'll have a wifi dongle attached to the USB. So I'm just being conservative. Probably 2A would be the most I'd ever draw, but I like to have a little extra. Besides, then I could add a future 5v device.



I think I've decided I'm going to put a PMC-06V-15W1AA inside the enclosure to power the Pi. Cheap & easy, and looks pretty good quality for a switching supply.
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Old 3rd September 2019, 03:11 PM   #8
nigelwright7557 is offline nigelwright7557  United Kingdom
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I have run a pair of fans off a positive rail of the amp with no problems.
So long as power supply can provide the right current there shouldn't be a problem.
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Old 4th September 2019, 03:51 AM   #9
benb is offline benb  United States
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5v regulator on positive leg of chipamp PSU
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Originally Posted by nigelwright7557 View Post
I have run a pair of fans off a positive rail of the amp with no problems.
So long as power supply can provide the right current there shouldn't be a problem.
Having TWO fans and not running one off the positive rail and the other off the negative rail is a sign of an unbalanced mind!
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Old 9th September 2019, 02:02 AM   #10
nigelwright7557 is offline nigelwright7557  United Kingdom
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Quote:
Originally Posted by benb View Post
Having TWO fans and not running one off the positive rail and the other off the negative rail is a sign of an unbalanced mind!
I ran the two fans in series so I am not dropping lots of watts in the resistors. Madness in my methods !
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