# [SOLVED] Voltage regulator now going negative



## Saturisk (Jan 2, 2011)

Hello, I'm not sure if this is the right forum for this thread, but here we go.

I am working on a portable Nintendo 64 and I just got the wiring the batteries together and started to plug them into the board. The board requires two voltages, 7.4 and 3.3. To drop the voltage to 3.3 I got a regulator from Texas Instruments Non-Isolated Module - Step-Down (Buck) Module - PTH08080W - TI.com (pth08080was) and I started to wire it up, using a 100uf 35v capacitor and a 2k resistor. The 7.4v going in works just fine but for some reason I am getting a negative value back out of it... I don't know too much about electrical components and I am kinda freaking out as I have spent waay too much money already to get blindsided by this.. Any help would be appreciated!


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*

Can you show us a photo of your wiring?

Are you saying that you are measuring -3.3V instead of +3.3V at Vout?


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

Correct, I guess I'm measuring it as negative 3.4v
Sorry for the fuzzy images:

This first pic is just my setup of the main components... All I'm really trying to do is is just get the light to come on to show that I'm wired everything correctly before I put everything else in.









This pic is the regulator itself (It was hard to take this pic)
The blue on the left is 7.4v in and the white w/ blue is the 7.4 out to the Nintendo. The instructable I looked at regarding this regulator said to use a 16v 100uf capacitor, but I only had a 35v 100uf capacitor at the time. Then the brown wire is the 3.3v out. Which is now giving negative current for some reason.









Then this is just the protection curcuit of the batteries.


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*

You don't appear to have connected a Ground wire.

BTW, using a higher voltage capacitor is OK.

Here is the actual datasheet for the module:
http://www.ti.com/lit/ds/slts235c/slts235c.pdf

... and here is the datasheet for the main IC (TPS54350) on the module:
http://www.ti.com/lit/ds/symlink/tps54350.pdf


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

Thank you for the speedy response!
I wasn't aware that it had to have a ground, with my limited knowledge of electrical circuits.. It works! Thank you so much!


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

Quick question, Just looking at the diagram I figured I would put the ground in the #2 part, middle of the in and out sides, and it worked for a little bit, but now it won't turn on. Just wondering how the ground should be set up as I am not well acquainted with electrical circuits..


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*

The middle pin of the three (ie pin #2) should be connected to the negative terminal of the 7.4V battery pack.


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

I feel like these are all little things.. I had it working with the ground in the second port, then I moved it to the box it was going to be in, and now the switch doesn't even matter, the thing has a constant 3.3v and 7.4v but it's not turning on.. I feel it's because I have two grounds running from the battery... one to the regulator and one to the n64, is that a problem?


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*

ISTM that your DC-DC converter is wired directly to the B+ of the battery, without going through the switch. Do you have any instructions for what you are doing?


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

Well with it there is B+ and B- for battery input and P+ and P- for charge out... wouldn't i connect it to P-?


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*



Saturisk said:


> Well with it there is B+ and B- for battery input and P+ and P- for charge out... wouldn't i connect it to P-?


Yes, you are correct. The load should connect to P+ and P-. I couldn't see the markings under the tape.

BTW, doesn't the N64 require a 12V supply rather than 7.4V?

Nintendo N64 power supply pinout and connections @ pinouts.ru

I would also suggest that you mount the DC-DC converter as close as possible to the N64.


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

It doesn't require it, it can run off of a minimum of like 6v or something like that, 7.4 is just an easy thing with the batteries I had.. I had a question regarding moving the regulator closer to the batteries themselves, because I have everything wired up the same as it was before only I have the on/off switch between the regulators 3.3v and the N64 instead of the 7.4v power. Problem is, it worked for like ten minutes and now it has constant power to both the terminals but the 7.4 is only like 4.0 or something and its not enough to do anything (and the switch doesn't affect it). I have tried looking at my solder jobs and nothing is touching anything.. Would it be that the wires from the regulator are too long and its maybe mistaking a ground for an actually wire or something? (Obviously not like actually mistaking it as electricity doesn't work that way) but I am seriously confused this time...


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*

Are you measuring 4V between P+ and P-?


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

I was measuring it from the com port, which now that I think about it would only get one of the batteries voltage, or half of the total voltage which is 8.12 right now... I get full voltage from P- and P+ until I hook up the ground.. Do you think that since the wires are pretty long it's not getting all the voltage it should especially with the way I had the ground? (I had it wrapped around my box probably twelve inches) I feel like my wires are just too long or something.. But the way I had it, It was recieving a constant flow of power and the only thing plugged in was the ground and 3.3v...


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*



Saturisk said:


> I was measuring it from the com port, which now that I think about it would only get one of the batteries voltage, or half of the total voltage which is 8.12 right now... I get full voltage from P- and P+ until I hook up the ground..


If you are connecting the COM and P- terminals together, then you are shorting one of the batteries. You should connect both your converter's ground pin and the N64's ground to P-, not to COM.


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

Oh no i only have the batteries runninh from the com and b+ and b-. I guess my real qiestion is, is there a possibility that my wires are too long so its not getting all the voltage it should?


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## fzabkar (Feb 7, 2010)

*Re: Voltage regulator now going negative*



Saturisk said:


> Oh no i only have the batteries runninh from the com and b+ and b-. I guess my real qiestion is, is there a possibility that my wires are too long so its not getting all the voltage it should?


Keep the wires as short as possible between the converter and the N64. That said, I can't imagine that the voltage drop would be excessive.

What voltages are you measuring at the N64?


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

I was measuring 8.12 and 3.3 but then something happened and it stopped sending me a decent signal.. I don't know. I'm in the process of neatening everything up. I think as for connections wise and for answering my original question I'm good. Thanks a lot! Haha


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## Saturisk (Jan 2, 2011)

*Re: Voltage regulator now going negative*

I can't tell if I'm just doing one simple little thing wrong, but so far i've fried two regulators... (By fried I mean I get the same input as output so I just figured I broke them...) Everything will be fine and I will have the ground and the positive 7.4 hooked up and the second I output to the nintendo, the regulator will seem fine but will get really hot and fry everything.. it literally desoldered itself (It's only cool because I haven't seen that before..) I'm not sure if I'm just wiring the wrong way or what..


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