Circuit examples, pros and cons

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ArakelTheDragon

Joined Nov 18, 2016
1,365
Hi!

I want to know if anyone has tried these circuits and tell me if he has met any pros and cons which I should consider.

3 to 5V shifter:
Pros are its simple, it has a minimum amount of components, SMD components can be used instead of normal ones, it can be used for fast switching up to 10MHz including on an SPI interface, it can be used in industrial conditions without any interference from the surrounding noise.

WiFI module:
Pros are its simple, it uses ESP8266 which will just be mounted on 2 pin headers making it easy to replace, it works well in industrial conditions, its possible to 256*256 modules with internal IP addresses
 

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Ian0

Joined Aug 7, 2020
10,277
Before you use a voltage shifter, check that you actually need one!
If the maximum value for Vih (the logic high threshold voltage) for your 5V part is lower than the output voltage of your 3V part, then you don’t need one at all. Vih for 5Vparts is often 2.4V.

Your choice of MOSFET is ridiculous. Why would you use a 30Amp MOSFET to switch a 500uA signal? There’s almost 1nF of capacitance to slow it down.

For a 3.3V input the MOSFET may or may not be switched on, because its Vgs(th) may be as high as 2V, so the circuit would be entirely unpredictable.

A 74LVC1G07 on the 3V supply and a pull-up to 5V on the output will do the job in A much smaller space than a huge IRLZ34.
 

Ian0

Joined Aug 7, 2020
10,277
As you are using SPI there are no bidirectional signals, you can just use open-drain logic to level-shift, or 74LVC which is 5V tolerant on its inputs.
 
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