Hello all,
This is a follow up on a previous thread I posted about using a SPDT relay as a power path switcher for the BQ25306 charging IC, because the relay enabled a higher current to be passed on to the system compared to the 3A limit imposed by the IC alone.
My follow up question relates to what is happening downstream of the power path- where there is a TPS62136 that manages the voltages applied to my loads (some thermoelectric modules).
Here's a basic schematic of the situation:
In it, you can see the relay controlling the power path- when a charger is NOT plugged in, the battery (an 8.4V 2S lithium battery pack) is connected to the Buck Converter load through the relay in the resting position. The node "Vsystem" connects the battery to some 5V regulators to power the microcontrollers, these are connected directly to the battery at all times for guaranteed uninterrupted power.
When a charger is plugged in, the relay is actuated, and the buck converter gets its current from the charger itself. The charger is a 12V charger.
Our concern is as follows- if the charger is plugged in, and the input capacitor to the buck converter (22uf) is charged to 12V, but then the charger is removed, what do we need to do to prevent that 12V from conducting in reverse back towards the battery, or will this even be an issue? How severe of a situation is it for there to be a capacitor charged like this connected to the battery through the relay?
If backcurrent is an issue, should we go back to our original post and go with a MOSFET power path instead of the relay variety, to prevent any reverse conduction? If the relay in this schematic was a P Channel Mosfet instead, would the capacitor be able to conduct back into the battery in this situation?
Thank you for your input,
-Uzair
