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  • Fundamentals
    • What is a resistor?
    • Ohm’s law
    • Kirchhoff law
    • Electrical resistivity
    • Inductance
    • Capacitance
    • Resistance
    • Resistor properties
      • Noise
      • Temperature Coefficient
      • Power rating
  • Standards and codes
    • Color code
      • Color code calculator
    • Standard values
    • SMD codes
    • Resistor Sizes and Packages
    • Symbols
  • Types
    • Fixed
    • Variable
      • Potentiometer
        • Potentiometer taper
      • Digital potentiometer
      • Rheostat
      • Trimpot
    • Thermistor
      • NTC thermistor
      • PTC thermistor
    • Varistor
    • Magneto resistor
    • Photoresistor
  • Materials
    • Wirewound
    • Carbon composition
    • Carbon film
    • Metal film
    • Metal oxide film
    • Thin and thick film
  • Applications
    • In Parallel
      • Parallel resistor calculator
    • In Series
    • Heating
    • LED Current Limiting
    • Power
    • Pull up / Pull down
    • Automotive Blower
    • Shunt
    • Braking resistor
  • Resources
    • Books
    • Suppliers
  • Capacitor
Tag:

pull down

  • Pull up resistor / Pull down resistor

    by resistorwp February 5, 2012
    by resistorwp February 5, 2012
    [caption id="attachment_1980" align="alignright" width="200"] Pull-up resistor circuit[/caption] What are pull-up resistors? Pull-up resistors are resistors used in logic circuits to ensure a well-defined logical level at a pin under all conditions. As a reminder, digital logic circuits have three logic states: high, low and floating (or high impedance). The high-impedance state occurs when the pin is not pulled to a high or low logic level, but is left “floating” instead. A good illustration of this is an unconnected input pin of a microcontroller. It is neither in a high or low logic state, and a microcontroller might unpredictably interpret the input value as either a logical high or logical low. Pull-up resistors are used to solve the dilemma for the microcontroller by pulling the value to a logical high state, as seen in the figure. If there weren’t for the pull-up resistor, the MCU’s input would be floating when the switch is open and brought down only when the switch is closed. Pull-up resistors are not a special kind of resistors; they are simple fixed-value resistors connected between the voltage supply (usually +5V) and the appropriate pin, which results in defining the input or output voltage in the absence of a driving signal. A typical pull-up resistor value is 4.7kΩ, but can vary depending on the application, as will be discussed later in this article. Pull-up resistor definition Pull-up resistors are resistors which are used to ensure that a wire is pulled to a high logical level in the absence of an input signal. What are pull-down resistors? [caption id="attachment_1981" align="alignright" width="200"] Pull-down resistor[/caption] Pull-down resistors work in the same manner as pull-up resistors, except that they pull the pin to a logical low value. They are connected between ground and the appropriate pin on a device. An example of...
    [Read more]
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