Hi.
I know how to do Simple LOW side switching of a load with a N-Channel MOSFET.
Question:
I am looking to be able to switch (on and off) the LOAD and Battery recharger (in parallel) with the same single MOSFET. (Fig. A.
Both share the same Neg. and Pos.
Problem:
(Fig A) The Battery Recharger (neg) is connected the DRAIN of the MOSFET. If the battery recharger voltage is higher than the battery voltage (recharging) it form the point of view of the recharger , this is now HIGH SIDE switching. Since in this case the SOURCE is less negative than that of the DRAIN, I may not be able to control the Battery Recharger properly. The current will now also flow through the Mosfet even when it is switched off.
If there is an issue with this, would Fig B or Fig C be good solutions?
If you can add an extra pin to your charger (split the ground signal to create an extra pin) that pin can be used as a disable/enable signal only when the charger is plugged in. I've used this method quite a few times on my projects
I just tested all three configurations.
In fig.A circuit works fine in terms of the load. BUT as soon as I connect the battery charger, the current flows to the battery EVEN if the MOSFET is OFF since now the current is glowing throught the body diode (i think) because at this point the drain is higher voltage than the Source.
In fig. B , current flows to both, the Battery and LOAD EVEN when the mosfets are OFF, current going through both body diodes.
In fig. C, same results as fig. A. Works fine with the load but is considered HIGH SIDE switching in terms of the recharger.
Any solutions?
I am looking to switch on / off BOTH the load to battery and recharger to battery at the same time with the same mosfet or even two mosfets. Basically doing HIGH switching in one direction and LOW switching in the other direction.
Both, the load and recharger share the same positive side and negative side (not possible to separate).
Maybe using a P-Mosfet in parallel with a N-Mosfet? Any suggestions?
Thanks sooo much.
I've been trying to figure this out, but I'm not able to understand your circuits, mainly because I can't see what's beyond the frame of the pictures. Could you post a more complete circuit?
In general, the charger circuits I've seen have a P-channel mosfet on the high side which is oriented "backwards", which orients the body diode so that it prevents USB power or solar power from flowing back into the battery, which you can't permit. Here's an example. I don't know if it's relevant to what you're trying to do.
Figure B. If you have connected the transistors correctly and they are off, no current can flow because the diodes are connected towards each other. Check your schema.
This is a well-known circuit and is often used to protect Li-ion batteries.
The DW01-P Datasheet says that FETs in the circuit do not work simultaneously, but in turn. Their gates are separately controlled. One transistor turns on charging and the other turns on discharging. Try to work in this direction.
