Looking for som PCB Help! 12v to Multiple Voltage Outputs.

Community PCB Design
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Hi everyone.

First I want to thank everyone for taking a look at my post.

Admission #1- I know very little about PCB design.

Admission #2- I am very interested in learning about it in practical application! I’m a very quick study!

I am a film student in Los Angeles and I have been thinking of designing a light weight “Battery Enclosure” that would take a 12v rechargable DC power source and distribute it to multiple variable outputs. I want to build a portable battery to use on my hand held Canon 7d shoulder mount. It would distribute power to the camera (7.4v) and various accessories (12v or 5v)

I am going to attempt to describe it, but please forgive me if I do not get the exact wording correctly:

A lightweight aluminum case with 4x Variable 2.1mm Coax outputs. Each output would have switch that would allow toggle between 12v or a 5v output. Plus a single 7.4v fixed voltage output (2.1mm). Perhaps a small LED indicator and a O/I switch.

Strong enough for field use.

If anyone is curious, the power source would be an compartment for interchangeable 12v 9800mAh batteries like this one:

http://www.camera2000.com/media/catalog … attery.jpg with Coax connections.

I’m here, because it seems like a community that is welcoming and knowledgeable.

I am not necessarily asking for a “freebie” but I’d like to find someone who could guide me through the process and help me with parts and technique. I’d like to learn how to do it, not just have someone do it. I’ve always wanted to learn this so I think this project is a great excuse!

I dont need my hand held, but just some guidance when I get off track.

If someone is willing to help me, I can offer some small compensation, or my girlfriend and I own a vintage clothing store in Los Angeles and I’d be more than happy to offer something in trade.

Thanks again for your time!

You can get back to me here through the board, or you can email me directly here: patrickmichaelclement[at]hotmail.com

2

The first thing you will need to figure out is how much current each output will need to provide. This will be needed to decide which voltage regulator to use.

/mike

3

Mike, thank for the first reply!

So this is an interesting question. In a perfect world, each output would be switchable between 5v and 12v. These are my most common power needs, and would it make sense to be able to adjust the output to fit whatever power was needed at a particular time? Is that possible? Some times I have two 12v accessories and two 5v accessories. Also sometimes I have three 5v accessories and only one 12v accessory.

A fixed output (12v) would work, i think, but many accessories, like my hdmi signal splitter, are 5v and would require an additional external adapter.

So, for my purposes, would fixed outputs with external adapters make sense? Or is it possible to switch between two different voltages (5v & 12v)?

Also, weight and cost are alway an issue ;-(0

Either way, my camera (Canon 7d) requires 7.4v as fixed output as well.

Thanks!!!

4

It’s not really possible for a power supply to determine what voltage is needed just from connecting the load. If you want it to be automatic in some sense, then what you could do is use a connector with an extra pin, and use that pin to control which voltage is provided.

Since you’re using a battery as your power source, I’m guessing you’re looking to make it last as long as possible - so I’d use a switched mode converter to generate the output. A buck-boost type will allow you to generate +5V as well as maintaining +12V even after the battery voltage has fallen below this level. National Semiconductor do a good range, and there’s a tool on their home page that can even do the design for you.

Whichever circuit you end up with, the output voltage is normally set with a potential divider connected between the output and the controller. You can add a third resistor which is either floating or grounded, depending on whether the extra connector pin is joined to GND or not.

(You could even put the resistor inside the accessory connector, and use that to set the output voltage on a per-device basis - just make sure the output defaults to the lowest possible voltage output when the connector isn’t plugged in properly!)

5

Thanks for the reply. I understand about …60% of what you said.

I’m going to spend the rest of the week trying to figure out the remaining 40%, so I can come back with some questions. :slight_smile:

6

Holey smokes…wait a minute…so can Webench basically design it for me?

7

So, back to the question that was never answered, how much current capability do you need for these outputs? That changes things drastically.

Have a look at

http://search.digikey.com/scripts/DkSea … 02-1709-ND

that’s a switcher module, 6.5 to 32 V input, 5V output, with 500 mA current. And its $5.78. Unless you really want the experience of designing your own switching power supply you should really consider something like that. You won’t find 7.4V, but you might find one that is adjustable. Look through the datasheet and then search digikey for more things in the “voltage regulator” category.

I’d strongly recommend having separate 12V and 5V connectors, that don’t interchange. If you use the same connector and rely on switches or some other mechanism, I can guarantee at some point you’ll get it wrong and let the magic smoke out of your camera/accessories. It’s darn expensive to refill electronics with the magic smoke. :roll:

If you want to minimize the number of connectors, I like the idea of using a three pin connector with 12V, 5V, and ground. Then you put the connector with the appropriate pin installed on your device.

8

Ok sorry, I hadn’t realized the question was relating to Amps and not volts. (this should hint at my level of knowledge.)

As far as I have read most of the 5v accessories would require <1amp and most of the 12v accessories would require <2amps.

I spent about 5 hours yesterday doing research and reading about building boards…and I have to admit. I’m intimidated.

I can sit down and read through a 1000+ page manual and actual understand it and I can debate European fiscal policies from the 19th century, I can tudor a classroom of students about evolutionary theory…but I am incredibly overwhelmed and intimidated by this process. I think it just makes me admire all the more, people who do this for a living.

I am almost convinced that it is utter out of my realm.

9

yrpfilms:
Holey smokes…wait a minute…so can Webench basically design it for me?

It can try. It's a useful tool, though it will always try and prescribe particular components which may or may not be readily available, or even suitable for your particular project.

There’s no substitute for delving into the data sheet for any chip you’re thinking of using and working through it, I’m afraid. Switchers can work very well, but can be an endless source of oscillation, instability and noise if you’re unlucky.