Battery power back-uped circuit

[Ioannis]

Roger, the minus Vgth is correct. Consider it a different visual angle!

In P-channel or PNP transistor the voltages are the opposite of the N-channel or NPN transistors. Means that the voltage og the gate in respect to the source is negative. The key to understand here is the term "in respect".

Ioannis

[flotulopex]

If I may ask further,

The "most important" value to take care off is the "Gate Threshold Voltage"; right?

It has to be as low as possible...but how low and why?



I thought RDSon value is very important too. But in this case, where the current is somehow small, is this less important in choosing the "right" MOSFET?