12v and 5v power supplies

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12v and 5v power supplies

This topic has 18 replies, 10 voices, and was last updated 20 November 2015 at 10:54 by Jake Atkinson.

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19 November 2015 at 13:11 #213170
Jake Atkinson
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@jakeatkinson60072
I have a small project with two circuit boards that both need different amounts of power. One needs a 12volt DC supply and the other needs a 5v supply using a mini USB cable. My question is, is there something i can use so that there is only one plug powering both?

Thanks
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19 November 2015 at 13:11 #31810
Jake Atkinson
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@jakeatkinson60072
19 November 2015 at 13:19 #213173
Emgee
Participant
@emgee
Jake

I have a similar project minus the mini usb cable. I am using a 12vDC supply to a pcb which also has a Voltage regulator on board to provide the stable 5vDC supply, I'm sure someone with electronic knowledge will provide a solution for you and list of parts needed.

Emgee
19 November 2015 at 13:21 #213175
Frances IoM
Participant
@francesiom58905
buy a power supply for a standard PC – often you can find throw out old PCs for free
19 November 2015 at 13:39 #213178
Ian P
Participant
@ianp
Jake

A one word answer would definitely be yes. However it really is a 'how log is a piece of string' type question so without more information (other than 'small' 'two circuit boards' it is impossible to say how to do it.

A vast quantity of electronic equipment operates off multiple supply rails but only has one sources of power so yours is not an unusual requirement.

Ian P

The smiley was not mine

Edited By Ian Phillips on 19/11/2015 13:40:10
19 November 2015 at 14:00 #213181
Frances IoM
Participant
@francesiom58905
5V mini USB sounds rather like a RaspberryPI which typically needs a little less than 2A – without knowing the amps at 12V somewhat difficult (common PC supplies give about 4A at 12V tho older models may well supply more) – if you need only about 500mA then one cheap option is the cigarette lighter to USB adapters sold at PoundShops fed from the 12V supply but these are not suitable to drive a RPi

Edited By Frances IoM on 19/11/2015 14:01:42
19 November 2015 at 14:13 #213184
John Stevenson 1
Participant
@johnstevenson1
http://www.ebay.co.uk/itm/110919861763

Edited By John Stevenson on 19/11/2015 14:13:46
19 November 2015 at 14:17 #213185
Martin Kyte
Participant
@martinkyte99762
DC-DC converter module?

Need some more details on current loads really.

Martin
19 November 2015 at 18:06 #213207
Alex Collins
Participant
@alexcollins55045
Hi.
Use an old PC Power supply. They are as good as free from old computers.

Google the Pin Outs. I made one with screw down Terminals on the top.
20 November 2015 at 08:23 #213258
Jake Atkinson
Participant
@jakeatkinson60072
Hi Guys,

I will detail as much as i can:

The 5v mini USB is to go into a Raspberry Pi B+ and the 12v is to go to a LCD screen controller board http://www.bonanza.com/listings/M-Nt68676-2-A-Hdmi-Dvi-Vga-Audio-Lcd-Led-Screen-Controller-Board-Diy-Monitor/296088874

The other problem i have is that the box that both of the boards will be housed in side of is only 150mm x 140mm x 30mm.

I have attached a 3d image of the project.

I have knowledge of electrics and am fairly proficient when working with them but with this being a power supply i want to make sure im getting it right.

Thanks for your help

Edited By Jake Atkinson on 20/11/2015 08:48:29
20 November 2015 at 08:35 #213259
Emgee
Participant
@emgee
Hi Jake

You need to state what the maximum current demand is for both the 12v and 5v supplies, if you are tight for space the external power supply looks the way to go.

Emgee
20 November 2015 at 08:56 #213260
Les Jones 1
Participant
@lesjones1
As others have said you have still not specified the current you require for the 12 volt supply. Does the power supply have to fit inside the box ? My approach would be to use a 12 volt external power supply and regulate the 12 volts down to 5 volts inside the box using a switch mode regulator from one of the pound shops as already suggested or one similar to this from one of the ebay sellers. I think you will find the Raspberry Pi uses a micro (Not mini) USB connector. One problem I have found is the resistance of many micro USB cables is quite high causing quite a large voltage drop on the cable. By putting the 5 volt regulator in the box will allow you to use a short cable for the 5 volt to the Raspberry Pi

Les.
20 November 2015 at 08:59 #213262
Jake Atkinson
Participant
@jakeatkinson60072
Hi,

The 5v will be around 300mA and im not too sure on the 12v but the screen is a LTN121W4-L01 touchscreen display and the powerboard is M.NT68676.2A. Hope this helps

Thanks
20 November 2015 at 09:04 #213263
Jake Atkinson
Participant
@jakeatkinson60072
Im open to having an external power supply and splitting the supply inside the box. Would the LM2596 be able to run both 12v and 5v at the same time though?
20 November 2015 at 09:28 #213269
Les Jones 1
Participant
@lesjones1
Jake,
It is impossible to answer your question of weather an LM2596 can supply a current of about as long as a piece of string. Measure the current your monitor takes or go for a large enough 12 volt power supply that will almost certainly be large enough say 10 amps. (I think this will be overkill but if you are not prepared to give the current reqired then all we can do is guess.) An LM2596 has a maximum output current of 3 amps so if you use a linear regulator to drop the 12 volts to 5 volts then this would leave 2.7 amps available for the monitor If you use a switching regulator (another LM2596 or an MC34063) to drop the 12 volts to 5 volts then this regulator would draw about 150 mA from the 12 volt rail leaving about 2.85 amps for the monitor.

Les.
20 November 2015 at 09:44 #213271
Paul Relf-Davies
Participant
@paulrelf-davies37806
Les,

I wouldn't recommend trying to power an RPi with less than a 1A supply. 500mA is about the minimum, but I've found they can be a little unstable with anything less than 1A, and more if you intend to power other devices (via USB, onboard GPIO, etc) from the RPi.

Also, why the LCD controller? The RPi outputs an HDMI signal, so why not just use a portable (ie 12v) LCD TV, such as this? After a little digging (and translation – its French) it seems that one draws 1A (12W at 12v) (and can run of batteries).

>>

cheers

Paul
20 November 2015 at 09:47 #213272
Martin Kyte
Participant
@martinkyte99762
Raspberry Pi B+ data sheet specifies 5V at 2Amps Power Supply requirement. Frances IoM has already stated this.

If you are starting with a single 12Volt supply if your switching regulator is going to take at least 833mA at 100% efficiency so budget for say 1Amp for the switcher load plus what ever you require for the monitor/controller.

Source something like a 3-4 Amp 12Volt external supply to give you some wriggle room and you are there.

Martin
20 November 2015 at 10:11 #213277
Bob Jepp
Participant
@bobjepp
I've used a few of these for work – they need a supply such as laptop power brick, but they give a good switched regulated supply.

Bob
20 November 2015 at 10:54 #213285
Jake Atkinson
Participant
@jakeatkinson60072
Hi, guys, would it be possible to use the below

http://www.ebay.co.uk/itm/Walvision-2-Way-DC-Power-Supply-Splitter-Cable-1x-Female-Input-To-2x-Male-Output-/311460190837?hash=item4884795a75:g:AtAAAOSwFnFWFO2S

and run one of the cables to the LM2596 which would then draw it down to the 5v to run the RPi?

And run the other to the LCD controller board for the 12v?

Thanks

Edited By Jake Atkinson on 20/11/2015 10:58:07

Edited By Jake Atkinson on 20/11/2015 10:58:26
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