Help troubleshooting Mosfets in Switching Circuit

[Sultanpepper123]

Hello,

I've been trying to design a simple circuit to switch between two Supply rails (3.3V_SW & Vbat) while giving one of them a higher priority (3.3V_SW). The circuit in simulation is showing to be not working well as shown below.



As shown above the toggling between VBAT (3.6V) &  3.3V_SW (3.3V) is unsuccessful , the transition from 3.6V goes down to 2.4V instead of 3.3V. 


 And I've built the circuit in person and the operation goes as follow, When the VBAT is activated the output is 3.6V (good) , when the 3.3V_SW is activated the output is 3.3V (good) . Now the problem starts when 3.3V_SW is deactivated the output is 3.3V instead of 3.6V coming from VBAT.

Would definitely appreciate it if anyone would share their insights on what might be the solution to make this circuit work as intended.

[Benta]

Your MOSFETs are upside down. And 470k is waaay too high for pull downs. the 2N7002 will supply more current due to leakage than those.

[TheoB]

Q5 source is tied to the internal bulk and needs to be connected to the highest voltage. Indeed source drain need to be swapped. Once switched on, you cannot switch off as vdd and 3.3V_SW are connected together by Q6. You have to short 3.3V_SW to ground to overcome this latched state. It does not work if you only leave it floating.
With no connection to 3.3V_SW, your circuit has two solutions, Q6 is on or off. That's not what you intended.