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 Forum index » DIY Hardware and Software
Switching Power Supply question
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flab



Joined: Feb 13, 2012
Posts: 60
Location: Glasgow

PostPosted: Mon Jul 15, 2013 3:23 am    Post subject: Switching Power Supply question Reply with quote  Mark this post and the followings unread

- i received a couple of switching power supplies the other day , well is this how you treat them if you want to get +/-15? plus im going to make another bus board +/- 12 through l7812 & 7912
cheers


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Osal



Joined: Aug 16, 2011
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PostPosted: Tue Jul 16, 2013 3:08 am    Post subject: Reply with quote  Mark this post and the followings unread

I would try it. I don't think that connecting two grounds can damage something.

Do you have more information about the power supplies? Model, brand, data-sheet?

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flab



Joined: Feb 13, 2012
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PostPosted: Tue Jul 16, 2013 4:42 am    Post subject: Reply with quote  Mark this post and the followings unread

well obviously that connection is the correct one , but do i have to connect the G to the bus board - i think not ,

here is the product http://www.ebay.co.uk/itm/300700312773

cheers


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Blue Hell
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PostPosted: Tue Jul 16, 2013 9:02 am    Post subject: Reply with quote  Mark this post and the followings unread

In that last image G (green wire) must be connected to the 2nd supply as well.

Or without a safety ground leave out all of the green wire BUT make sure to have everything double insulated then and that when a mains power wire comes loose it can not possibly touch any metal parts (by using tie-wraps / heat-shrink tubing).

The GND for the busboard comes from the grey wire that connects +V from the left (negative) supply to -V of the right (positive) supply.

Optionally you can connect the mains G (green) to that grey wire as well - depending upon your, or your country's (this varies wildly over the world), ideas about grounding equipment and safety.

For safety people recommend to make that connection - but it only makes sense really when you are going to use it in a wet room or outside.

The drawback can be that you create a ground loop that may cause hum in a more complex setup.

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flab



Joined: Feb 13, 2012
Posts: 60
Location: Glasgow

PostPosted: Thu Jul 18, 2013 7:40 am    Post subject: Reply with quote  Mark this post and the followings unread

appreciate - works fine now , i tied the G with the common -V +V
cheers
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Osal



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PostPosted: Thu Jul 18, 2013 8:22 am    Post subject: Reply with quote  Mark this post and the followings unread

If the the negative terminal is not referenced to the Ground I think you could also to connect the ground to the ground terminals. Did you do it like this?

Another thing: Because you can set the supply up 16.5V, you could use a low dropout regulator to achieve 15V with better performance.
(In the same way you will use standard regulators to achieve 12V)

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piedwagtail



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PostPosted: Thu Jul 18, 2013 11:47 am    Post subject: Reply with quote  Mark this post and the followings unread

It's all relative you can connect ground to nominated 15, the nominal 0V or nominated -15.
It only matters when you interface to a ground in another system.

If ground is on the free -V, centre-tap will 15V and free +V will be 30V.
Contained within the system opamps will sit happily at work elevated to +15V in that scenario.

A npn transistor will work for instance between 0 and -15V (or say between 15V and 30V etc) the collector to 0V and the emitter to -15V.
I have a -15V supply pnp germanium preamp with a n-channel jfet as an output driver, the output capacitor protects the system. The jfet is oblivious.

I did receive my supplies but I've been pissing around with upics .
Amazing to get a possible 2A from a cigarette carton.

Robert
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flab



Joined: Feb 13, 2012
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Location: Glasgow

PostPosted: Tue Jul 23, 2013 7:37 am    Post subject: Reply with quote  Mark this post and the followings unread

well in more detail thats my what im planing to breadboard

-so i supply a idc from -15 +15 straight from the power supply plus a +5V from the 7805 , and from the -12 +12 idc through the 7912 & 7812 , oh and i did placed an 1A fuse for the -/+12 rail

- i haven't try it with any modules yet - i dont want to see anything turn to ashes -

any safe mods to be made ?


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elmegil



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PostPosted: Tue Jul 23, 2013 10:54 am    Post subject: Reply with quote  Mark this post and the followings unread

You still don't show the mains ground being connected to the positive supply....
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piedwagtail



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PostPosted: Tue Jul 23, 2013 11:11 am    Post subject: Reply with quote  Mark this post and the followings unread

Yes as Elmegil says Mains earth Green should be connected to
Quote:
1.the ground of the specifications smpsu on left
2.the ground of the other smpsu on the right(needs to earth the box from a shorting failure)
3.the +V of the specifications smpsu on left
4.the -V of the other smpsu on right


thick wire short path

7812 and 7912 will shut down with any short
Will need capacitors between the outputs of all three of the regulators and the ground.
47uf 25V and 100nf in parallel
note electrolytic will be positive to +12 on the +12 rail and positive to 0V to the negative -12 rail.


Robert
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LED-man



Joined: Feb 22, 2013
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Location: Germany

PostPosted: Thu Aug 08, 2013 4:00 am    Post subject: Reply with quote  Mark this post and the followings unread

you have to secure the transistors by a diode, between output to input, because in some cases the Enddevice have bigger caps as your transistor end caps. many guys don´t have use this in the layouts and are wondered about defective voltage regulators and defective caps.
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flab



Joined: Feb 13, 2012
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PostPosted: Thu Aug 08, 2013 8:05 am    Post subject: Reply with quote  Mark this post and the followings unread

well ,
here is the update power supply wiring thanx to the piedwagtail, and I also add capacitors (47uf 25V and 100nf in parallel) between the outputs of all three of the regulators and the ground ,
led-man thanx for the extra tip - i ll install an 1n4004 diode to all three regulators


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flab



Joined: Feb 13, 2012
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PostPosted: Thu Aug 08, 2013 8:10 am    Post subject: Reply with quote  Mark this post and the followings unread

oh i made a mistake at the wiring diagram on top - the ground at the left power supply box is connected at the G and the + V not the - V
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piedwagtail



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PostPosted: Fri Aug 09, 2013 5:55 pm    Post subject: Reply with quote  Mark this post and the followings unread

Quote:
3.the +V of the specifications smpsu on left


Circuit Ground to wall earth!

Please update your diagram....you're disturbing me!
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