Best way to detect what power source is connected?

Hi,

I'm designing a circuit that can accept 3 sources of power:

• Solar
• DC
• AC

1 or more power sources could be connected at the same time. I've attached a simplified diagram of how I think the key parts should be arranged.

What I'm trying to figure out is the best way to determine what source is providing the most amount of power. Can I simply measure the voltage and current at a point before each ideal diode?

Thanks,
Steve

 

Thanks Harold,

I'm fairly new to all this stuff and I'm learning as I go. I'm thinking of using the LTC4357 (http://cds.linear.com/docs/en/datasheet/4357fd.pdf) as the ideal diode. I haven't chosed the MOSFET part yet. I don't believe this diode controller part provides any intrinsic status, or perhaps I'm not understanding your comment "It should be easy to take the information which ideal diode is 'on' from the respective control circuits."

But, if I understand correctly, by simply reading the current before each diode I can determine which diode is (or isn't) active? I haven't breadboarded anything yet but I'm looking forward to trying things out soon.

Much appreciated!

Steve

 

Thanks! I hadn't thought of that approach. I'll definitely try that as my first option, it may also save on some parts

I very much appreciate the support and collective wisdom from this forum.

Steve

 

Harald,

You mentioned that this approach is an "ab(use)" of using the MOSFETs gate. I'm curious, would this be considered a hardware "hack"? Would this approach be frowned upon in a professional design? I plan to try it out soon, but I'm also wanting to learn and apply best practices. As I said, I'm just curious and wanting to learn.

Thanks,
Steve

 

Thanks Steve,

Yes, I see that it's taking advantage of the gate signal that was not intended to be used for another purpose, but could this approach still be considered acceptable? I'd be interested to see a schematic that made this "dual signal" idea work.

Steve

 

My idea is to use the application notes and part references in http://cds.linear.com/docs/en/datasheet/4357fd.pdf to have a 3-way OR-ing ideal diode setup for a max 36V @ 10A. The MOSFET specified is the Fairchild FDB3632 (https://www.fairchildsemi.com/datasheets/FD/FDB3632.pdf). Eventually, I need to send a digital signal to a microprocessor to indicate which power source is providing the power hence the need to "read" the active MOSFET and provide this status.

Please forgive the newbie question, but when you say "the drive to the MOSFET gate is fairly "stiff"" do you mean that the voltage or current should remain steady as it drives the gate?

Based on the choice of driver and FET, how would you suggest I proceed? I'm hoping to order the parts from Digikey later this week and start breadboarding something.

Thanks,
Steve

 

Thanks again.

I'm actually a "hybrid" Kiwi. I moved to New Zealand from UK and became a naturalized citizen. I now live in USA.

 

Thanks. Yes, I'm fairly new to all this stuff (particularly analog electronics). I'll do as you say once the parts arrive.

Steve

 

Thanks,

Yes, I think this an excellent idea, and in fact this was the direction I was going initially. If the MOSFET gate idea doesn't work I will probably fall back to this approach. My motivation is to reduce the number of parts and cost of the overall design. I like the Allegro parts very much and am quite familiar with them.

Steve

 

Thanks for the suggestion. Honestly though I think this will consume too much board space and create unnecessary noise. Also, I'm concerned about the possibility of eventual mechanical failure, particularly since the application will be used in a high-stress (knocks, bumps, vibration) environment. For these reasons I'm probably going to avoid using relays.

Steve

 

I'm planning on using resettable fuses on each input. Do you think another one of the main bus is also required?

Steve