Connect with us

Choosing resistor value

Reply to Thread

Discussion in 'General Electronics Discussion' started by steve_venkat, May 25, 2017.

Scroll to continue with content
  1. May 25, 2017 #1
    steve_venkat

    steve_venkat

    30
    0
    May 22, 2017
    I noted this in PIC16F877A controller.They mentioned into current maximum to VDD is 250mA. While choosing resistor across power supply and VDD means we having use 250mA maximum value to find out the specific resistor value or have to use any lower value below 250mA...?
     

    Attached Files:

    • 123.jpg
      123.jpg
      File size:
      91.3 KB
      Views:
      45
  2. May 25, 2017 #2
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    No resistor is required. You must design your system to keep within the budget.

    It's a bit like the maximum load rating for a truck. You don't ask what cost per pound you need to charge to avoid overloading the truck, you weigh the boxes and make sure the total weight is ok.
     
    Arouse1973 and steve_venkat like this.
  3. May 25, 2017 #3
    steve_venkat

    steve_venkat

    30
    0
    May 22, 2017

    Thanks for your kindly reply...
    I can't understand this line "you weigh the boxes and make sure the total weight is ok"..

    Are you suggesting to calculate something else..?
     
  4. May 25, 2017 #4
    Audioguru

    Audioguru

    2,976
    667
    Sep 24, 2016
    The maximum allowed current into the IC is 250mA. You do not use a resistor to reduce the current, instead you do not overload the IC. If the IC has no load then its current is only a few mA.

    The battery in a car can supply 400A to the starter motor when it is very cold. But the clock in the car does not use 400A, instead it uses only about 10mA. A resistor does not limit its current, instead its design and loading determine its low current.
     
    steve_venkat and davenn like this.
  5. May 25, 2017 #5
    davenn

    davenn Moderator

    13,668
    1,891
    Sep 5, 2009
    yes

    read AG's post --- specifically the first bit

    you need to consider the loads on the outputs of the micro and ensure that they do not, when combined, exceed 250mA
    I would make sure they don't exceed around 200mA ... I wouldn't want the micro operating anywhere near its max


    Dave
     
    steve_venkat likes this.
  6. May 26, 2017 #6
    steve_venkat

    steve_venkat

    30
    0
    May 22, 2017
    1.In PIC16F877A they mentioned like this..If i used all ports as OUTPUT means the IC will be overloaded right..?
    2.If I used PORTB as INPUT and PORTC is used as OUTPUT means,the output current will depend on VDD..?
    3.Or output of each port is depend on VDD..?
     

    Attached Files:

  7. May 26, 2017 #7
    (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,418
    2,788
    Jan 21, 2010
    No. All of the ports might be outputs, but the current drawn from them might be a fraction of a milliamp.
     
    Arouse1973 likes this.
  8. May 27, 2017 #8
    BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Calculate the current drawn from pins that are outputs and high and add them up.
    Extra credit: Calculate the max current drawn from all pins that might be high as the same time.

    Bob
     
    Arouse1973 likes this.
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Similar Threads

  1. choosing a resistor value

  2. Help! Need advice choosing proper resistor value.

  3. Resistor value

  4. Resistor Value

  5. Resistor Value.

  6. Resistor value

  7. Resistor value identification

  8. Resistor Value Identification Help

Loading...
Electronics Point Logo
Continue to site
Quote of the day

“”

-