Electrical – Block current flow in one direction with FET transistors

battery-chargingmosfetprotection

Is it possible to block current flow in one direction like a simple diode using FET transistors to avoid the voltage drop?

schematic

simulate this circuit – Schematic created using CircuitLab

I am not talking about reverse polarity protection. With VS>0 and Vbat>0 if Vbat>VS the current flow from battery to power supply.
I want that the current only can flow from power supply to battery, so always Ich > 0.

I am reading this document from Texas Instruments: http://www.ti.com/lit/an/slva730/slva730.pdf
But I don't understand how figure 4 works. How the gates of P-channel MOSFET are driven? The FET configuration is symmetrical, how is it possible to block only the current in one direction?
enter image description here

Best Answer

You ARE talking about reverse polarity current protection, you said:

".. if Vbat>VS the current flow from battery to power supply."

This is a reversed polarity current.

Every MOSFET has a parasitic body diode structure. So even when it is turned OFF, it doesn't block the current if it goes in opposite direction. To completely block any current in OFF state, two transistors are needed, which is illustrated in the Figure 4.

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