First, I'll go through what I think is going on in this circuit. If I understand it correctly it's basically a logic converter. The 3v input comes from STM32 GPIO and the output goes to a floppy disc controller.

When 3v3 input is low the inverter will raise the voltage on the gate of the transistor, transistor will open and the 5V will be pulled to ground and there will be no output. So when there's no voltage on the gate, transistor is shut and output will sense 5V on the line.


simulate this circuit – Schematic created using CircuitLab

Assuming that my analysis here is correct, I am wondering if I could possibly replace this this whole part with an IC?

I have six lines that need level shifting and I found TXB0106 IC. It says that it is a bidirectional level shifter and voltage translator. Reading the specs I figured I could just replace the inverter IC, resistor, mosfets and the 5V pull-up resitor with this IC.

I set VCCa to 3.3V, VCCb to 5V, OE pulled to high, take care of decoupling and then just use the input and output for each line that I need.

Because this seems a little bit too easy, I have a feeling that I'm not seeing something and I'm missing some detail that will break my design.

I know that I don't actually need a bidirectional converter, but this one fits perfectly so I'm not going to be pedantic about it.

So, any ideas why it might not work and if there are better solutions, I'm open to all the suggestions.

  • 1
    \$\begingroup\$ If you're going to buy a gate, just get a non-inverting open drain buffer. \$\endgroup\$
    – The Photon
    Aug 17 '19 at 19:13
  • \$\begingroup\$ Why not a simple pair of npn transistors and a pull-up. \$\endgroup\$
    – User323693
    Aug 17 '19 at 20:32
  • \$\begingroup\$ " the output goes to a floppy disc controller." - which floppy disk controller? Are you trying to emulate a disk floppy drive? \$\endgroup\$ Aug 17 '19 at 23:13
  • \$\begingroup\$ @BruceAbbott yes, it is a floppy disc emulator. People have been using Gotek floppy emulator for quite some time and I'm making a few modifications to it and I'd like to get rid of as many parts as possible and this would be a very nice reduction because I could replace almost 20 components with a single IC and a couple of decoupling caps. In the end I want a PCB that would fit inside some of the old computers. \$\endgroup\$
    – BigWhale
    Aug 18 '19 at 17:38
  • \$\begingroup\$ The TXB is unlikely to work with pull-up/-down resistors or weak input signals (see the datasheet). \$\endgroup\$
    – CL.
    Aug 20 '19 at 13:44

If you have the ICs already in stock (or in mind), then it is perfectly fine to go with those ICs. As a good design practice I would first check basic need of voltage level translation. The chosen IC is for the same purpose.

enter image description here

The other minor things you should also look at is:

  1. Power consumption
  2. Maximum operating speed
  3. Behaviour during floating input signals
  4. Price
  5. Space on PCB

  6. What if the output is meant to be open collector?

Alternate Circuit 1
enter image description here The component count is way lessthan the present solution. Cost is next to nothing.

Alternate Circuit 2

Simple to understand. Input is supplied at the base in the left side of the image. Output is tapped at the right hand side enter image description here


To power up a device it mat be active low logic or + 5V low resistance but unlikely 0V low resistance. Thus to need to consider a high-side switch with a PCh FET Driver

Whether you want a non- inverting or +ve logic function means the input need to be an NPN common-emitter to perform also as a level shifter .


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