# P-channel MOSFET switch - very high Rdson

I am trying test my p-channel mosfet (IRF9Z34) high side switch on load. On circuit simulator I get the result I expect, Rdson (VM1) is low and load current is 1.4A. (In the target system the gate will be controlled, here the mosfet is always on for tests). T1 - P-MOSFET IRF9Z34.

In the real circuit current is max 0.9A, so I have very big Rdson, I don't understand why. Vgs > Vth, The power supply has a current effiency > 2A.

• What is the $V_{gs}$ used to specify the $R_{ds}(on)$ in the datasheet for your MOSFET, and what $V_{gs}$ are you applying? Apr 14 '20 at 18:00
• It looks like the 5V is too low to fully open this MOSFET
– G36
Apr 14 '20 at 18:01

If your voltage is at least 10V you're guaranteed to have < 140 m$$\\Omega\$$ Rds(on) with the junction at room temperature (more when hot).
At Vgs(th) - which could be as high as 4V, you are guaranteed to have at least 250uA flowing so equivalent resistance of 16k$$\\Omega\$$.
For example, an AO3401A has less than 60m$$\\Omega\$$ Rds(on) with a 4.5V drive voltage.