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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Sat Jun 01, 2019 2:55 am Post subject:
Two 7809 ground loop |
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Hello,
while designing a power supply pcb for manufacturing, a question popped up. The systematic of the circuit looks about the same as this one here: https://cdn.instructables.com/ORIG/FZG/YM90/G5703OX4/FZGYM90G5703OX4.jpg
I am using two 7809 and now I wonder what happens if I connect both pin 2 to common ground and also using the same, big heat sink for both regulators (so both to220 heatsink junctions are connected to ground). Isn't this closing a form of ground loop? Somehow I can not really think straight, right now.
Thank you! |
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Sat Jun 01, 2019 3:02 am Post subject:
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I know it is a pretty common thing to do, but my brain is telling me something is wrong. |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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Posted: Sat Jun 01, 2019 12:38 pm Post subject:
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I am pretty sure pin 2 is physically connected to the backside of the regulator, so by mounting them both on the same heatsink
you're basically just creating a lower resistance between pins 2 of both regulators, which is a good thing. At least that's what I think.
I might have some old broken TO220 component I can crack open to check. _________________ "My perf, it's full of holes!"
http://phobos.000space.com/
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Sun Jun 02, 2019 4:30 am Post subject:
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Hey Phobos,
thank you very much for your answer. Today my brain is not that foggy anymore and I think what you said is completely right
Actually I could use a multimeter to check if those things are physically connected haha. I'll do it later.
EDIT: So i did test it, they are connected! .00 ohm between them hehe |
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PHOBoS
Joined: Jan 14, 2010 Posts: 5591 Location: Moon Base
Audio files: 705
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kaputtpanzer
Joined: Nov 02, 2009 Posts: 139 Location: Cologne
Audio files: 15
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Posted: Sun Jun 02, 2019 3:36 pm Post subject:
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Oh wow thanks for the good picture! Very interesting indeed!
Well, the plan is to power some guitar pedals with the two regulators, that share the same heatsink. I think, what you said about the cable is right. I have built a few circuits where I accidentally made some ground loops. It was never a problem, when it was inside one circuit. Probably the cables play a big part. I almost never have this common ground hum in my circuits and signal paths.
But when I power a few pedals with my psu, my circuit should provide the best possible current and stable voltage. But I guess I will just, have to make some measurements when it is finished. Actually if pin 2 and the heating tab is connected inside the regulator, there is not a real ground loop. In the worst case, the regulators need some of these heatsink isolator things. |
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