Component selection for an automatic voltage switch

Thread Starter

cowhock35

Joined Dec 25, 2012
48
I'm working on a product that will run off of either a solar/battery input or a power supply. I would like to make the circuit boards all the same, and they will include a built in MP1584 buck converter as a voltage regulator. The issue is that when hooked up to solar the input voltage is high enough the regulator operates fine but when hooked up to the power supply at ~6.2v, the input voltage drops to under 5v after it passes through the converter which isn't enough to even power up the Atmega328. The regulator's only purpose is as a charge controller for the battery. There is an on-board 5V linear regulator for the board electronics.

I'm trying to come up with a way to design a automatic switch, either using analog components or an IC that will detect the input voltage and if it is lower than 7V, bypass the buck converter and go straight to the circuit board/battery. If higher than 7V, pass through the converter.

I'm looking for a solution that is going to be relatively simple and very inexpensive, >$1 per board on a 500 unit order. The simple, cheap, and failsafe workaround would be to put a DIP switch on the board that manually selects the solar or AC input before they ship. If there was a cleaner solution though, I would like to find it. My knowledge base is not deep within EE so I don't know if perhaps there are some basic ICs or components that I'm not aware of that would make this a simple design.
 

Thread Starter

cowhock35

Joined Dec 25, 2012
48
The converter is appropriate for the solar input and output. But the power supply output is much lower and that's the issue. We already have lots of power supplies so getting a custom or different power level won't be ideal. The product has already been designed and sold and this is a mid-cycle redesign so some of our constraints are limited.
 

ci139

Joined Jul 11, 2016
1,680
if it is lower than 7V, bypass the buck converter and go straight to the circuit board/battery. If higher than 7V, pass through the converter.
you do realize - that when power goes through the Step-Down the input voltage is supposed to drop
what it means is - that detecting your input voltage in operation is a bit tricky
. . .
what you may attempt is that - if the output starts to drop - you switch to SMPS by pass (PMOS + OC or OD comparator + somehow the shutdown/standby control signal to mp1584 . . . or another PMOS to cut it's input off)
 
Top