# P Channel mosfet seems to put out the voltage of the MCU input

I built this circuit, exactly, with the exception of the Zener.

When I test the output of the Channel mosfet, it shows approx 2V below whatever voltage I used to trigger the gate on the N channel side.

For example, if I place 12V on the N channels gate, the P channel Drain, measured at the drain is 10.5V, and if I put 24V on the N Channel's gate I get 21.3 on the P channel's Drain.

I have searched and read and all seems to point that I should be getting approx 24V (VDD)-IlRDS at the drain.

What on earth am I not understanding here? Surely, irrespective of whether I apply 12 or 24 to the N channels gate, should I not be getting 24V-IlRds on the P channel's drain? Why am I getting 10.5 or 21.3V on the drain?

• If you're putting 24V on the gate of the IRF3205, you've destroyed your IRF3205. It's rated for a maximum $V_{GS}$ of 20V. – Hearth Oct 27 '18 at 13:16
• On top of that, if that zener diode is not populated as stated in your question, you've probably also destroyed your IRF4905, because when the n-channel fet is on, $V_{GS}$ on the p-channel one goes to -21.8V according to a quick simulation, which is also exceeding the maximum of ±20V. – Hearth Oct 27 '18 at 13:19
• Also are you sure you got the pin assignments of the FETs correct? A photo of your physical circuit could help us check that. – The Photon Oct 27 '18 at 15:55
• Tend to agree with @ThePhoton here, and think there is a connection issue. While you are exceeding the abs max ratings, they virtually never fail that close (24V vs. 20V) to the rating. – Spehro Pefhany Oct 27 '18 at 16:07
• Thanks a Lot guys! I shall rebuild and add the zener and report back! – Paul Ferreira Oct 27 '18 at 22:19