A friend asked me to help him with a small project he is working on.
I've thinked of a couple of solution but are quite complicated and doesn't cover all the requirements at once:
- Two power busses
- 12V battery in (standby)
- 8-26V DC In (active)
- 12V@3.5A (max not continuous) regulated output
- DC IN must have reverse polarity protection, UVP, OVP (to protect switching converter)
- When DC IN fails, (no present, UV cut off, OV cut off) it must immediately switch over to 12V battery.
- When DC in come back switch over must be performed after DC IN has a power good signal for some time. (To prevent to switching when the PSU hiccups)
The only solution for this that is coming to my mind is using an MCU. - The OVP/UVP and the active/standby status must be capable to be monitored by and external MCU/CPU.
My solutions fails to do this. In fact any additional load that i attach to the two voltage references to handle OVP/UVP will unbalance the gate network.
Resulting in the P MOSFETs that I'm using as a switch are always open. - And it must be Cheap!
I'm attaching my idea below, but as I said before it is convoluted and not properly working. (It is also missing the reverse polarity protection.)
In that simulator the voltage references component is not present, so i had to create them manually!
And it is missing the DC DC part for the 12V stabilized output, but that should be the easiest part.
![](https://i.ibb.co/HT4X3Pz/PWR-Switch.jpg)
Any idea is welcome!