Power Supply Question and Request.

Question

Hi People - i have a request for the members for assistance.

Brief Background - I build Robots and Drones - both ground based and aerial. My background is programming not physical design....

My request is this:-

A power circuit capable of taking in at least 36v dc and outputting any and or all of the following 3,3v 5v 6v 7.4v 9v 10v 12v -- these are the standqrd voltages required by our robotics platforms.

The input voltage needs to be anywhere from 6v to at least 36v - although higher is ok.

The out[uts would ideally be switchable and selectable so that at least any 3 of those voltages could be output at once - ie 3.3 and 5 and 10 volts out all at once....

I dont know if this is possible or not - thats where you come in ....

If possible i would like a schematic and a BOM to build this..

Please help

Cheers

Al

jw0752 · Answer

Hi Al,

What you describe is possible, but to build a universal supply will not be as efficient as building to a specification. For a specific application one would need to know the voltage of the source of power. The amount of current that the source can deliver would be a limiting factor on the outputs. For example the voltage of your source times the limit of its current will define the wattage of the source. The voltages of your secondary systems times each of their respective currents are the power in watts that is being consumed by your device. The power consumed can't be greater than the power available at the source. You would need to know the different voltages that are needed as well as the current that will be needed for each voltage. There is a big difference between building a 5 volt one amp supply and a 5 volt 10 amp supply. I am not an engineer and so I have found for my own projects that there are a lot of DC to DC converters commercially available at reasonable prices that I integrate into my designs. Most of these converters use switch mode power supply (SMPS) designs and are very efficient. (Some in excess of 90%). this is very important particularly if your device is running from a limited supply such as a battery. Many of these converter modules will take a range of voltages for input and deliver a range of voltages for output. In this way I can input from 4 V to 36 V and get 1.2V to 34 V out. These are called BUCk converters as they reduce the voltage. Here is an example of a BUCK converter:

http://www.ebay.com/itm/DC-DC-CC-CV-Buck-Converter-Step-down-7-40V-to-0-8-35V-12A-Power-Supply-Module-/272614244686?hash=item3f7913414e:g:p7QAAOSwuLZY39YW

You can see where a series of these converters could be tied into a voltage source and each be tuned to a specific output voltage. As long as your device doesn't try to draw more current than the device is capable of they seem to work very well. Of course for the money they are great for non-critical applications. I would not recommend them for any critical or medical application.

Rather than continue to ramble I will send the conversation back to you and we can expand the discussion if this is what you are interested in.

I call my approach to design the Borg approach as I do not design new technology by rather assimilate the designs of others.

John

dougw · Answer

You could try one of the design tools that guide you through complete solutions.

Like TI tools:

Power supply design for single loads | WEBENCH tools | TI.com

SWITCHERPRO SwitcherPro(TM) Switching Power Supply Design Tool | TI.com

Or Linear Technologies

Solutions - Designing Power Supply Parameters in Five Simple Steps with the LTpowerCAD Design Tool

Jan Cumps · Answer

Al, your first post mentions input from 6 to 36 V. Some of your desired outputs are higher than 6 V. I it's a requirement to have outputs that can be lower as well as higher than the input, a Buck design will not do. A Buck-boost design can handle that.

jw0752 · Answer

Hi Al,

If some of your circuits require less than 1 A there is a nice series of DC to DC converters from Recom. They will convert up to 28 volts in to fixed 3.3 V, 5 V, 9 V, 12 V, and 15V, at 1 amp and do it with nearly 90% efficiency so there is no a need for a lot of heat sinking. Further they are quite small. Here is a link to the 5 volt unit.

http://www.newark.com/recom-power/r-78e5-0-1-0/dc-dc-converter-5w-5v-1a-sip/dp/83X9336?ost=R-78E5.0-1.0&scope=partnumberlookahead&exaMfpn=true&searchref=searchlookahead&searchView=table&iscrfnonsku=false&ddkey=http%3Aen-US%2FElement14_US%2Fw%2Fsearch

If you want more than one Amp then it will require extra work. I suspect that one could put in the support hardware for the higher amperage output and perhaps use the little DC to DC converters as Plug in voltage selectors to drive the components that would deliver the higher amperage.

You might note that while you will get questions answered and a lot of help on the forum it is unlikely that anyone will design the circuit for you. For one thing there may be liability issues if something that is designed fails and property is damaged or people are hurt. Some of the guys on the forum do circuit designs for a living and you may be able to contract with one of them to do your design for you but they will have to speak for themselves. I personally do not have the skills yet to take on a design project for someone other than myself. If you can find the resources to start designing and prototyping the board that you want I am sure that there will be help with the bumps in the road from the guys here.

John

eye-zen · Answer

So this is where im at so far - and it looks like it might work for me - just need to work out the BOM and then see how feasible it is size and cost wise.. thanks everyone for your input and assistance..

Power Supply Question and Request.

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