Author Topic: Power Supply Question  (Read 734 times)

skypn

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Power Supply Question
« on: July 29, 2020, 01:49:06 AM »
Hey Guys, I've got a question about the power supply section of a circuit. Here is the whole schematic:



and the section in question:



I realize that this section is providing two different voltages. Is it also providing polarity protection? And if so, which components are doing that? I've seen it done with a diode before so I'm wondering.
Knowledge for knowledge's sake.
TIA   

mjg

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Re: Power Supply Question
« Reply #1 on: July 29, 2020, 02:20:20 AM »
Nope, I canít see any polarity protection there, unless Iím missing something.

For comparison, there is a similar circuit on NucleonFX at the moment that does have a diode protection: https://www.nucleonfx.com/screen/product/fusion
« Last Edit: July 29, 2020, 02:27:20 AM by mjg »

FuzzMonkey

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Re: Power Supply Question
« Reply #2 on: July 29, 2020, 02:24:10 AM »
There is no reserve polarity protection in that particular power supply section. Adding a simple diode such as a 1N4001 like you may have seen in other schematic provides a basic level of protection.

Something like this:

« Last Edit: July 29, 2020, 02:27:39 AM by FuzzMonkey »

mjg

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Re: Power Supply Question
« Reply #3 on: July 29, 2020, 02:29:22 AM »
I think people have migrated to using a 1n5817 in series these days, rather than the 4001 option.

Max

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Re: Power Supply Question
« Reply #4 on: July 29, 2020, 02:48:09 AM »
I think people have migrated to using a 1n5817 in series these days, rather than the 4001 option.
Yep, at least I did.

JackSkellington

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Re: Power Supply Question
« Reply #5 on: July 29, 2020, 02:55:44 AM »
Rather, it seems to me that the 1N5817 has replace the 47R, and in that case I think a diode across the ground is unnecessary.
ęJust because I cannot see it doesn't mean I can't believe itĽ

Max

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Re: Power Supply Question
« Reply #6 on: July 29, 2020, 04:00:20 AM »
It has replaced the 1N4001 in the sense that it's an entirely different approach, not that it's in the same place. Plus you don't need R7, which is there to limit the current in case a reverse polarity is applied, because the 1N4001 would create a short to ground.

danfrank

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Re: Power Supply Question
« Reply #7 on: July 29, 2020, 01:48:45 PM »
Hey Guys, I've got a question about the power supply section of a circuit. Here is the whole schematic:



and the section in question:



I realize that this section is providing two different voltages. Is it also providing polarity protection? And if so, which components are doing that? I've seen it done with a diode before so I'm wondering.
Knowledge for knowledge's sake.
TIA

A thing to note... R7 and R8 should be matched for identical value. This creates the biasing voltage for the op amps

skypn

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Re: Power Supply Question
« Reply #8 on: July 30, 2020, 12:59:03 AM »
Thanks for the all the help.
mjg...once I get this circuit worked out on my breadboard, I will build the one you suggest on a different breadboard to do a side by side comparison to see which I like better.
My original question was answered, but like in so many other things in life, the answer just raised more questions.
Like, what is the difference between the PS I posted, and FuzzMonkey's? Is one superior to the other, or just two different ways of doing the same thing, or maybe its the old everything is a trade off thing?
I see the difference in the components.
D3 in FM's is providing the polarity protection, I see that. Why is C4 in mine eliminated, and what was it's purpose in the first place?
R7 in FM's added, and the matching values of my R7 and R8, and his R5 and R6 different...Is it because the two are supplying different secondary voltages?
Would simply adding a 1N4001 to my snippet add the wanted protection?
Am I over thinking this? Are the questions I'm asking show I'm still too far over my head in all this?
TIA

skypn

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Re: Power Supply Question
« Reply #9 on: July 30, 2020, 01:02:32 AM »
After rereading the post, I retract my FM's R7 question, as Max has answered it. Sorry, early morning ;D

mjg

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Re: Power Supply Question
« Reply #10 on: July 30, 2020, 02:55:27 AM »
C4 and C5 are stabilising the power supply voltage. Same for C4 in the other schematic.  They are all doing the same job, but having two of them of different values is able to keep the voltage stable better, or handle different frequency variations in your power supply. 

R7 and R8 are forming a voltage divider between V+ and ground.  Because the values are both 10k, the voltage divider is going to end up half way between V+ and ground.  So about 4.5 volts if the input is 9v.  The value of 10k isnít so important, but the fact they are the same value as each other is important to get 4.5v.   

To add protection to your original schematic, I would add the 1n5817 diode between the input voltage and V+, like shown in the other nucleon schematic I linked to.  The idea of that is if you reverse the voltage, nothing happens, and no current flows. 

The 4001 approach also works, but people have moved away from it.  If you reverse the voltage on that one, you still get current flowing.  It will protect your circuit, but current still flows through the first resistor and the diode.  And if you donít add that first resistor at all, it's a short circuit, which isnít great for your power supply. 

Keep asking questions, itís a good way to learn stuff.  🙂


Rockhorst

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Re: Power Supply Question
« Reply #11 on: August 03, 2020, 02:01:09 PM »
Someone called?

The updated version / build doc of that schematic, including the 1N5817, can be found here: Nucleon Fusion Clean Blend. That may help you out.

If you're using stripboard or anything, what 'parent pcb' do you want to mix clean into? Tap off the power after the polarity protection on that board and use that to power the blend circuit.

About C4 in the original schematic as you posted: use a MLCC cap valued 100n or higher (like 1u or 10u, they are available, cheap and small). They do a much better job of filtering the power than regular film capacitors. It helps with some extra smoothing/decoupling. I find that these caps work very well when place close to opamps from the power line to ground.

Cheers :)
« Last Edit: August 03, 2020, 02:05:52 PM by Rockhorst »

skypn

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Re: Power Supply Question
« Reply #12 on: August 05, 2020, 02:33:22 AM »
Thanks for all the help guys

skypn

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Re: Power Supply Question
« Reply #13 on: August 10, 2020, 03:47:09 AM »
Rockhorst:
I am assuming that the Clean Fusion is yours.
To answer your question, the "parent board" I'm using is the Bass Fuss. It doesn't have a power supply, just a 9v tap, which I was just going to add the 1n4001 polarity protection to, so I guess I'll tap into the fusion's PS.
I (attempt to) build from schematics, and etch my own PCB's.
What is the difference between "jump" and "omit" in the BOM? Does "jump" mean replace the resistor with a wire, and "omit" mean leave the connection open?
Also, in the PS section, there is two 9v+ taps before the connection to the 9v+ pad. That confuses me.
I would like to thank you in advance for your time and expertise in answering my questions.

Rockhorst

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Re: Power Supply Question
« Reply #14 on: August 10, 2020, 05:56:21 AM »
The picture you posted has a nucleon watermark on it, that's the name of my little pcb company (see my signature).

Jump means: wire the two pads together, so you make a connection but there's no component. You 'jump' from one place of the schematic to the other.

Omit means: install nothing, not even a jumper wire.

Whatever takes the external power from a battery or power supply to the rest of the board we'll refer to as 'power supply' or section. If you want to install polarity protection use the 'in line' diode method and use a 1N1518, not the 1N4001 parallel. The latter will just burn up and scorch your board. It's just a way for companies like Boss to tell if you misused the pedal and voided your warranty.

The multiple 9V and G points are just to allow for flexibility so you can keep wires shorter and fit your needs. They are all connected with each other directly through a +9V plane and a ground plane (copper fill on the board).
« Last Edit: August 10, 2020, 06:03:50 AM by Rockhorst »