Electrical Engineering Stack Exchange
Electrical Engineering Stack Exchange

Questions tagged [logic-level]

Logic level refers to the input and output voltage levels of digital logic, which is often 3.3 V or 5 V.

Logic level is relevant when driving MOSFETs directly from a digital output. Previously this was often 5 V, but today's logic ICs often operate at 3.3 V or lower. Power MOSFETs often need higher gate voltages to drive the rated current, and most manufacturers filled the gap by producing several logic level MOSFETs with a VGS(th) of 2 V or less, which can drive several amperes at 3.3 V.

Logic level is also important when connecting logic ICs operating at different supply voltages.

Further reading
Logic signal voltage levels information on All About Circuits

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Step up 3.3V to 5V for digital I/O

I normally use an Arduino for my projects because it has 5V inputs and outputs and has 5V Vin so that makes life very easy when interfacing with 5V components. For this project I want to use a Raspberry Pi because I want to hook it up to a display.…
Huckle
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How did people realize they could do logic with electronics?

How did people realize they could do logic with electronics? Are there anecdotes or records of the first realizations? I'm wondering about the first "eureka" moments.
Kinnard Hockenhull
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Single transistor level up shifter

I need a simple, single directionnal level shifter for 3.3V -> 5V conversion. There are many options on the internet, some using a logic ic and some using 2 NPN transistors (converter and inverter), but I never found an option using only a single…
Nicolas D
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7400 series CMOS vs 4000 series logic IC

I understand the traditional difference between the 7400 series and the 4000 series logic ICs, but since there are CMOS versions of the 7400 series, is there an advantage to use the 7400 CMOS version over the 4000 series chips? Please note I'm not…
bit0fun
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What does the voltage of an I/O pin mean?

I'm trying to figure out the Seeed Studio XIAO board (essentially a smaller version of the Arduino) and I noticed that there was a line in the specifications saying "All the I/O pins are 3.3V, please do not input more than 3.3V, otherwise, the CPU…
Rena W
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Should I use CMOS vs. TTL?

Now, I know that this question has been asked so many times that it seems like I'm trolling, but I must point out that I couldn't find the right answer to this question anywhere. So yeah, CMOS and TTL are different. Logic levels, speed, drive…
fuzzyhair2
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How to convert a digital signal from 24V to 5V

I have an industrial automaton that gives me a digital signal (24V or 0V) on its outputs and I want this signal to control an integrated circuit, but the integrated circuit only takes a TTL signal in its input (0 to 5V). I think it can be controlled…
Pierre B
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Fast bidirectional 3.3 to 5V level shifter

For a hobby project of mine, I'm thinking about connecting some old 5V SRAM chips like this one to a 3.3V - capable FPGA. The target frequency is 50MHz. After some simulator experiments I found out that a simple voltage divider could work: simulate…
Dmitry Grigoryev
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What's the purpose of this diode in this level-shifter?

look at this circuit: I don't get that what's the usage/purpose of the BAS316 in this circuit?
Roh
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Translating to "below ground" logic levels

I have an RF switch chip that is controlled by a logic signal with levels of 0 V and -3 V. I want to control this from a CPLD that's producing ordinary +3.3 V CMOS levels. Board area is at a premium in this design because I'm trying to wedge this in…
The Photon
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Logic-level transistor not switching

I am trying to use a transistor to drive a lamp from a Raspberry Pi (3B+) and I went after one that can be switched by the 3.3V logic. I found the FQP50N06L to have a max Vgs threshold of 2.5V, so it should work (right?). Here's the circuit I am…
Lurosset
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Replace BSS138 with AO3400A in level shifter circuit

I have to use level shifter circuit to interface MAX31855 with Arduino running on 5V. I found easy to build level shifter circuit at SparkFun website. It is using BSS138 (datasheet) which I don't have. I am thinking to build same circuit with…
Junaid
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How do I invert a signal without deforming it, and without using a logic gate?

I have an IC which outputs pulses over an open collector pin. I need both these pulses and their inverses in my circuit. I want to do the inversion by using as few as possible transistors and without using any ICs. First, I tried simply inverting…
hkBattousai
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Driving a 74HC245 in one direction with 3.3V when Vcc is 5V

I have a 5V device that accepts parallel data in. That data is buffered by a 74HC245 IC (TI datasheet, NXP datasheet) where the Dir pin is hard wired to drive in one direction. I can't change/modify this device hardware-wise. To date I have been…
sa_leinad
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ESP32 logic HIGH/LOW level voltage, not working?

From ESP32 datasheet: In my case: VDD = 3.3V Vil (max) = 0.25 * 3.3 = 0.825V Vih (min) = 0.75 * 3.3 = 2.475V Theoretically: LOW LEVEL range is -0.3V to 0.825V HIGH LEVEL range is 2.475V to 3.6V But when I tested practically: LOW LEVEL range is 0V…
Pradyum Aadith
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