Why does this MOSFET not switch 9 V?

Question

I am designing a circuit so that I can mute/unmute a microphone using an Arduino/Raspberry Pi.

I am using a CD4051 which is designed for controlling audio applications. The schematic is based off of this blog.

I am using a dual rail power supply with +9 and -9 V on the CD4051.

CD4051
pin 16 = +9 V
pin 7 = -9 V
pin 11 = audio select (low 0 V = active, high 9 V = inactive)

Because the Raspberry Pi GPIO pins use 3.3 V, but the CD4051 uses 9 V, I am attempting to use a IRLZ34N N-channel MOSFET as a logic-level converter.

Problem

This logic level circuit should allow a 3.3 V microcontroller to toggle a 9/0 V on the CD4051 (pin 11).

Yet when I prototype this circuit, I measure 3.3 V at pin mic_A (and pin 2 of the MOSFET). I've double checked my circuit, and even compared to this blog article.

This is how the circuit performs in the simulator (I am using 5 kΩ resistors instead of 10 kΩ, and using an IRLZ34N instead of a BS170)

What is wrong with this logic-level converter? Why am I not getting 9 V at pin mic_A?

• https://thetuberoaster.wordpress.com/2020/09/25/cd4052-audio-signal-switch/
• https://circuitdigest.com/tutorial/bi-directional-logic-level-controller-using-mosfet

---

Update

Why use an IRLZ34N?

Because thats the only TTL N-channel MOSFET I currently have.

Here is a photo of the prototype:

Update 2

After further experimentation, I was able to get this working and have the IRLZ34N to be switched with 3.3v logic.

However based on the comments, I have also learned

1. BS170 is a better suited mosfet for this application since the IRLZ34N is intend for high current
2. +9V/-9V is not required for the CD4051
3. Logic Level Conversion is not necessary since the CD4051 logic can be controlled with 3.3v
4. I should add bypass capacitors to the power rails of the CD4051

Video of working circuit: https://www.youtube.com/watch?v=3zxkHmgybTc

Answer 1

Checking the datasheets from both MOSFETS (BS170 vs IRLZ34) I see three main differences:

1. Their \$t_{on}\$ and \$t_{off}\$ times, where the BS170 turns on in 10 ns (MAX). The IRLZ34 indicates a rise time \$t_r\$ of 100 ns (the datasheet does not indicate a specific \$t_{on}\$ rather a \$t_{d(on)}\$ or turn-on delay time of 8.9 ns (Typical))

2. Their input capacitances. For the BS170, \$C_{in}\$ is 40 pF (MAX) while \$C_{in}\$ for the IRLZ34 is significantly higher at 880pF (Typical). Proving a slower response time from the latter.

3. In terms of the \$R_{DS(on)}\$, the IRLZ34 outperforms the BS170, however, the test conditions and application scenario are abysmally different (low-voltage, low-current switching vs high-current switching).

These criteria are the ones proposed by Nexperia on its application note AN97055 for \$I^2C\$ Bi-directional level shifters:

Finally, this guide on MOSFETS parameters might help you to clarify all of these numbers.

The bottom line is: each type of transistor has its own application case.