Questions tagged [pulldown]
A pull-down resistor brings a line down to a voltage (typically ground potential) when the line isn't being driven to a specific voltage. It prevents the line from "floating" with an unknown voltage on it.
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Thoroughly confused about open drain
I've been reading a tutorial on open drain and I'm thoroughly confused.
First, the terminology makes little sense. How can a resistor pull up or pull down current when its job is to resist current? ...
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Datasheet says pull up/down resistors are not necessary, but application of part uses resistors?
I am using a TPS2546 in a USB charging hub, and I'm basing it on a preexisting design I found online (link to writeup for design). In the schematic for the hub design the ILIM_SEL, EN, CTL1, CTL2, and ...
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TP4056 power cutoff circuit using PFET
I want to understand this and also to make sure this will work.
This is a TP4056 USB-C charging circuit. The circuit is almost the same as the regular one you'll find ordering from China. The only ...
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Active pull-down in LSTTL totem-pole output
The lower totem-pole transistor of a LSTTL IC frequently has an active pull-down from base to emitter (ground). Here is an example from TI's SN74LS93 datasheet.
I was curious how this active pull ...
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Pulldown resistor between ICs?
I'm building a 24hr clock out of discrete logic, and I forgot to include pulldown resistors, so I'm going back and adding them. I know to put pulldown resistors on the switch inputs, but do I also ...
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How is a "smart pull-down" implemented
Some devices have a smart pull-down resistor. It is active until the user drives the pin, and as soon as a threshold is reached, the pull-down is deactivated.
How is this implemented, e.g. if I wanted ...
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Calculating the lowest value MOSFET pull-down resistor
I am using the AO3415 to do high-side switching.
My aim is to reduce power consumption as this low-power device should run for ages on a single battery. System quiescent current is less than 5 μA. (...
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Do I have to use pull up/down resistor with switch with common terminal?
I have seen some examples why we need to use pull up/down resistors, but do I need to use it if I use switch with common terminal?
If I have the schema like so, do I need to use the pull up/down ...
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Why is this variable not updated during the loop?
I`m trying to obtain a PWM signal from RA4 a PWM signal when a button is pressed (button connected to RA2) using a PIC12F1572. I'm in trouble with code because run as follow:
Start simulation via ...
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How can I control PNP and NPN transistors together from one pin?
I'm trying to understand how it is possible to control a PNP and a NPN transistor simultaneously from one controlling pin.
My issue is that when the INPUT pin is left floating, the transistors drive ...
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Battery isolation circuit with inverted logic
I asked a question some time ago in regards to preventing back charging my back-up battery question. I was just using a diode, but a circuit was suggested for more protection. It doesn't lend itself ...
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"Pull-up" and "pull-down" or "push" and "pull"?
I thought about this question when I read an interesting comment by @Simon Fitch in his answer.
In the complementary amplifier stage, in total there are three "pulling" elements - Q2 is a &...
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Configuring S32K148 Microcontroller 144pins LQFP pin no 113(PTA1) as pull down
I am using S32K for current measurement purpose.
Using pin no 113 as ADC input.
I can see in the datasheet that ,we can configure this pin as pull down or pullup.
May I know is this possible to set ...
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L6924U output status pins in the datasheet description are open-collector, but schematic shows a MOSFET
The battery charger L6924U has two status pins, ST1 and ST2, to tell what is happening inside the charger: charge in progress, charging done, stand-by mode, etc.
In the datasheet STM always writes ...
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MOSFET + voltage regulator usage, pull downs, common ground, schematics
As a continuation of my previous question about what type of part I'd need to control a circuit with a higher voltage, I put together schematics for what I hope would achieve what I am looking for ...
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Floating ttl input and ground short without pulldown
A pulldown resistor seems to always be used for configurations where when the switch is open the normal state is low.
For example
The reasons always given are to avoid a short between voltage and ...
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USB-C pulldown resistors before or after common-mode choke?
I'm designing a board with a USB-C upstream-facing port (UFP) for power only (no data). I've included a common-mode choke, as well as a ferrite bead filter in pi configuration. Since I'm presenting as ...
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Why do we connect unused (always low pins) pins to GND through a resistor instead of connecting it directly to GND?
I have been reading the datasheet of RV-3028-C7. Everytime it talks about a pin that might be unused in a certain scenario (should be logic low), it instructs to connect the pin to ground through a ...
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"Pull-Down Resistor" in AC circuit
Background
I have an Fridland AC doorbell that I am about to make "smart". My approach is to connect a device named a shelly uni inside the doorbell that ...
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GPIO with no pullups or pulldowns
I have a SPDT switch connected to a GPIO pin on an nRF52810 microcontroller.
The switch has two positions:
Shorts the GPIO to GND
Shorts the GPIO to V+
The switch is used to toggle a software ...
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What is the point of configuring an output as "push-pull" and "pull-down" at the same time?
In CubeMX, there is still "pull-up" and "pull-down" options listed for an output while that output is already configured as "push-pull". How does it make sense to ...
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How to calculate the pull down resistor value for an input pin in a 74HC273 flip flop?
An old circuit I'm checking was built using a philips 74HC273 (CMOS dev) datasheet in a card that is receiving reset and other signals from another card. In that other card, reset signal comes from a ...
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Which one is better to use for micro controller input mode? Pull-up or pull-down?
As you know it's better to keep micro controller in "Sink" mode instead of "Source" of energy because it keeps micro controller safe and stable.
For the input mode of an AVR (or ...
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MCU Built-in Pull Down
I'm using a Microchip PIC24FJ1024GA606.
I have two versions of my PCB and I am using a pin to identify the hardware revisions. On Version 1, the pin is unused and on version 2, the pin is connected to ...
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Pull up and down resistors at the same time
I have an I2C circuit with a 4.7 kohm pull-up resistor for each line. I think it might be a too strong (too small in value) resistor and the data isn't read properly. The processor I'm using has the ...
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Do I need a pull-up / pull-down resistor to sense 12 V on the 12V_IGN rail in an automobile?
I'd like to start / stop a piece of software running on an in-car computer depending on the 12V_IGN rail going on resp. off. This happens when the ignition switch goes in / resp. out of position RUN. ...
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Do I need a pull-down resistor with this MOSFET-based motor driver?
I'm using the circuit in the picture to control a 12 V DC motor with an ESP32.
Do I need an extra pull-down resistor between the microcontroler pin and ground to avoid my pin floating and maybe ...
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What does a pull-up or pull-down resistor actually "pull"
What does a pull-up or pull-down resistor actually "pull"? What does "floating" value mean? What is "floating"? Eg. in this picture, if there is no 10K resistor then the ...
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explain high and low state
I have a TP4056 module (datasheet: https://dlnmh9ip6v2uc.cloudfront.net/datasheets/Prototyping/TP4056.pdf). It charges a 18650 cell.
According to the datasheet :
(Pin6): Open Drain Charge Status ...
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Pull Down resistors value for unused pin for MCU
According to the datasheet, it is preferred to have MCU's unused pins connected to GND. That's the only thing suggested in the datasheet. I think it would not be a wise decision to directly connect ...
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Pull up / pull down resistor value
Wanting to calculate the value of the pull down resistor for a 555 trigger. For the formula should I use the typical or max trigger current (typ = 0.5 Max = 0.9 μA). I want the calculated value not an ...
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Adjusting the drive strength of level-sensitive interrupt signal
In my current environment, the interrupt source comes from an FPGA on a daughter board and connects to a GPIO pin on an EVB:
daughter board (interrupt output signal from SD controller)--> EVB(GPIO ...
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Do circuits with pull up resistors waste more electricity than circuits with pull down resistors?
A pull up resistor provides a constant voltage (and therefore some current) to an input pin on arduino.
https://learn.sparkfun.com/tutorials/pull-up-resistors/all
A pull down resistor connects an ...
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Analog sound data
I tried to make my own sound sensor on a PCB. I wanted to take analog sound data for my project. I used an ADC pin from a STM32G474, but I maded mistake while I designing. I took a KY-038 reference ...
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Unclocked NOR gate SR latch not latching [closed]
I am starting to learn computer architecture and decided to try building an SR latch using NOR gates and without a clock (basically copying this video) on a breadboard.
My circuit is pictured, it is ...
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Op-amp burns out [closed]
On my PCB the input of the op-amp is shorted to VCC (28 V) or GND when the op-amp burns out (it happens a lot).
In addition I want to add protection components on the input of the op-amp; if the op-...
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Pull-up and pull-down resistor on one trace
Does it ever make sense to have both a pull-up and a pull-down resistor on the same trace?
Background:
I'm designing a backplane to follow the OpenVPX guidelines and I saw this rule
Rule 7-20: The ...
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Pull output down if either of multiple pins are pulled down
(Sorry in case I used the wrong terminology, let me explain.)
Context
I have a relay board I'm controlling. It has 8 relays, and 8 low level triggering pins for control.
7 of the relays I want to ...
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Why would a digital input require a pulldown instead of a direct connection to the input voltage?
I've seen datasheets for certain ICs recommend using a 100 kOhm (or so) pulldowns or pullups for setting configuration inputs. What could be a typical reason for this? Normally I would just tie the ...
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Reduce current through a pull-down resistor when chip power is removed
For a battery-powered application, I'm trying to reduce the current draw of a chip when its voltage rail is removed.
What is the current through the enable pin's pull-down resistor when the 5V USB-...
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Find Vout with voltage divider + pull-down resistor
I have to calculate Vin (~5 V). After using the voltage divider formula the Vout value is pretty close to the value measured by a multimeter, but a little bit low.
The question is, what is the formula ...
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Do you need a current limiting resistor on an enable pin?
I am using MCP16312-E/MS buck regulator and need the component to always be on. I am therefore connecting the enable pin to the Vin supply. Do you need a current limiting resistor? Whilst the resistor ...
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Buttons in parallel - short circuit? [closed]
I encountered a problem while trying to use 21 buttons at the same time. Initially, I did not take into consideration that they could be pressed all at once. And while measuring the resistance I ...
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Are pull up and pull down resistors required?
I am trying to design PCB with a W5500 and an RP2040. I have some questions. I read the W5500's datasheet. In this photo, it says pull-down and pull-up for some pins but in the example design they ...
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Using shared pull-down resistor or providing pull-down for each mosfet
There are some P channel and N channel mosfets which operate as swiches in figure 1. Also, there is a pull-down resistor for each mosfet which prevents the mosfet's gate being float when the VCC is ...
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Why is pull down resistor path of least resistance for the "floating" noise?
This question often pops up from people learning about pull up/pull down resistors. Why people ask it, is easy to see, it is a logical question to ask.
If the pull-down resistor is bypassed at logic ...
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"Hardware shut off" pumps when water leak is detected
I did a lot of research but cannot find a clear solution to my problem - maybe that's also because of a lack of understanding proposed solutions, of course. After all I read, I feel confident enough ...
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Can pull-down resistor be connected before the gate resistor?
I noticed I have made a mistake in one of my PCBs and have connected the pull-down resistor of a MOSFET before its gate resistor (point A), rather than to the gate directly (point B, see schematic) as ...
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Should a pull resistor be on the main MOSFET or at the driver?
I want my MOSFET to be initially "off" by default.
I can’t decide whether to place the pull resistor on M1 or M2 (pull up at M1 and pull down at M2). My typical instinct would tell to ...
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Calculation for Resistor in Phototransistor Emitter
I decided to ask here for help, I am still new at electronics, I have been trying to figure out the definitions and graphs of this phototransistor, the PT1302 (datasheet here), my doubt is how can I ...
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