Timeline for Single transistor level up shifter
Current License: CC BY-SA 3.0
24 events
| when toggle format | what | by | license | comment | |
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| Mar 21, 2023 at 15:21 | comment | added | Nicolas D | @ScottM I'm actually not quite sure I got your question right. On a more basic level, you don't "expose" the pin to 5V if there is a resistor between the 5V and the pin. If the pin is an output (or an input with protection diodes), significant current can flow safely through the pin and the external resistor ; therefore U=RI voltage is dropped. | |
| Mar 21, 2023 at 15:15 | comment | added | Nicolas D | @ScottM Microcontrollers usually have input protection diodes (diodes to Vcc and from ground). If the current is not limited they'll fry all right, along with the rest of the chip ; if the current is limited to a value those input diodes can handle, they'll just clamp the voltage to the rails, up to the forward voltage drop of those diodes. You'll have to refer to the specific microcontroller's datasheet to know the acceptable limits, and adapt resistor(s) values accordingly. | |
| Mar 18, 2023 at 14:11 | comment | added | Scott M | @Nicolas D Ok, so the current is low, but I thought Arduinos were sensitive to voltage as well, and anything over 3.3v presented to a GPIO pin would damage them, regardless of current. Is that only true if the pin is an input? | |
| Mar 17, 2023 at 13:55 | comment | added | Nicolas D | @ScottM I don't think so. The transistor is conducting when the input side (which is some kind of digital output) is pulled down; in that situation it's expected to be able to swallow a reasonable amount of current - less than 1mA in the example. | |
| Mar 8, 2023 at 13:33 | comment | added | Scott M | I have a question on this. When the transistor is conducting, doesn't this dump +5v into the 3v3 logic source? A lot of microcontrollers seem to fry if exposed to 5v even at very low current levels. Wouldn't this kill most Arduinos, etc? | |
| Aug 18, 2019 at 22:23 | history | protected | Nick Alexeev | ||
| Jul 7, 2017 at 15:28 | comment | added | Sridhar Rajagopal | You can use a bi-directional level shifter using n-channel mosfet without logic inversion. See this thread - electronics.stackexchange.com/questions/313869/… | |
| Dec 1, 2015 at 16:05 | comment | added | Nicolas D | @RespawnedFluff thanks for the biblio! I was pretty certain that it was either wrong or very old tech. Now I know it works and I have the refs - nice! | |
| Dec 1, 2015 at 15:04 | comment | added | got trolled too much this week | I found your solution in a somewhat confusingly written appnote: silabs.com/Support%20Documents/TechnicalDocs/AN883.pdf They actually do bidirectional translation (on their SDA line), with one direction (low to high) being exactly like yours. They measured only 150mV saturation with a MMBT3904 when doing 1.8V->3.3V translation. | |
| Dec 1, 2015 at 14:25 | comment | added | got trolled too much this week | Also, you have pretty much rediscovered US patent 3283180, from the 1960s. | |
| Dec 1, 2015 at 12:21 | comment | added | got trolled too much this week | Something like this is better with a FET: electronics.stackexchange.com/questions/97889/… | |
| Oct 18, 2014 at 0:23 | comment | added | tcrosley | Schematic looks fairly good to me also. Olin can be a little picky. It's missing a junction dot on the bottom of R2, and the Q1 designator should be next to the transistor. Also, a part number for the transistor should be shown (e.g. 2N2222). It's got the input on the left and output on the right, which is correct. | |
| Oct 17, 2014 at 23:55 | comment | added | pericynthion | The schematic looks pretty clear to me.. | |
| Sep 12, 2013 at 13:22 | vote | accept | Nicolas D | ||
| Sep 12, 2013 at 12:47 | comment | added | Olin Lathrop | Ug. You should draw your schematics more sensibly layed out, especially if you ask others to look at them. What you have is a simple circuit, but I had to tilt my head and think about it to realize what it is actually doing. With a proper layout that would have been immediately obvious, and might help you see what is really going on in the circuit too. (For more info see electronics.stackexchange.com/a/28255/4512 . ) | |
| Sep 12, 2013 at 12:16 | history | tweeted | twitter.com/#!/StackElectronix/status/378129884050362368 | ||
| Sep 12, 2013 at 11:46 | answer | added | Tut | timeline score: 10 | |
| Sep 12, 2013 at 10:55 | comment | added | Anindo Ghosh | @medivh I just simulated it with a 2n2222 spice model, and the voltage goes from 0.14 Volts to 4.92 Volts. A perfect low level of 0 Volts is not really needed for most digital inputs. | |
| Sep 12, 2013 at 10:53 | answer | added | Anindo Ghosh | timeline score: 22 | |
| Sep 12, 2013 at 10:52 | comment | added | shieldfoss | @AnindoGhosh True. Still not equal to 0 though. | |
| Sep 12, 2013 at 10:50 | comment | added | Anindo Ghosh | @medivh It would give Vce(sat) as the output voltage at 0 Volts input - and for many small signal transistors, Vce(sat) is far smaller than the diode drop, e.g. 0.3 Volts maximum for the 2n2222. | |
| Sep 12, 2013 at 10:46 | comment | added | shieldfoss | Well for one thing, a 0V input gives a 0.7V output with this design. | |
| Sep 12, 2013 at 10:29 | review | First posts | |||
| Sep 12, 2013 at 10:29 | |||||
| Sep 12, 2013 at 10:09 | history | asked | Nicolas D | CC BY-SA 3.0 |