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Topic: Question on a design by adafruit - level shifting (Read 436 times) previous topic - next topic


The adafruit esp8266 board:


Nice big picture shows two diodes marked as B5 serving as 3.3V to 5V level shifter (left side 5V, right side 3.3V). Their schematic say 1N4148 but I don't know if that was correct. They probably only wanted the SMD footprint to be correct.

I found the diode to be OnSemi B5 ESD protection diode, essentially a transient voltage suppressor for 5V devices:


So my question is: do TVS get regularly used for voltage level shifting in industry? I'm not an electrical engineer so I don't know if this is a common practice. Thanks.
Serial LCD keypad panel,phi_prompt user interface library,SDI-12 USB Adapter


Aug 14, 2016, 10:50 am Last Edit: Aug 14, 2016, 10:51 am by Graynomad
That will work if the right side has a pull up resistor to 3v3.

As for a TVS diode being used, maybe they have a smaller Vf so the low voltage level is better (IE lower) on the 3v3 side, but I don't know why if that's not the case.
Rob Gray aka the GRAYnomad www.robgray.com


No, the design only has a pullup to 3.3V on RESET. The RX is directly connected to ESP8266. Maybe ESP8266 has an internal pullup. But won't this design require some largish current to pass through the TVS from the 5V side? Say the 3.3V RX is connected to the diode/TVS, and the same junction is connected to a resistor then 3.3V power, then the junction would be somewhere above 3.3V when the 5V RX is HIGH, am I correct?
Serial LCD keypad panel,phi_prompt user interface library,SDI-12 USB Adapter

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