pic internal shunt voltage regulator

Discussion in 'Embedded Systems and Microcontrollers' started by Svizoman, May 18, 2017.

  1. Svizoman

    Thread Starter New Member

    Oct 23, 2016
    8
    0
    I am using PIC16F616 in my design and I looking at the page 107: SHUNT VOLTAGE REGULATOR
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    It says that you can use unregulated power supply directly to the Vdd pin. It eliminates the need for linear voltage regulator, you only need capacitor and a resistor which value should be calculated as follows.
    Capture.PNG

    Since I am using car power supply (let's assume it's 14V) and controling two NPNs over 10k resistor my Iload is just 1mA.
    So Rmax=171 4 ohm and Rmin=189 ohm.

    Then I am also reading chapter: electrical specification where it says that voltage on Vdd with respect to Vss can be -0.3v to +6.5V.
    What does that mean? Can I power my pic using car voltage and only internal voltage regulator or not?

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  2. AlbertHall

    AAC Fanatic!

    Jun 4, 2014
    6,698
    1,581
    First it is only the 16HV616 that has the internal regulator (not 16F)

    Second your resistor values are wrong
    upload_2017-5-18_17-23-47.png
    VUmin = 11V (min car battery voltage)
    VUmax = 15V (max car batter voltage)
    Iload = 1mA (we'll go with our figure)
    Rmax = (VUmin - 5V) / (1.05 * (4mA + Iload) = (11V - 5V) / (1.05 * (4mA +1mA) = 1.14kΩ
    Rmin = (VUmax -5V) / (0.95 * 50mA) = (15V - 5V) / (0.95 * 50mA) = 210Ω
     
    ErnieM and JohnInTX like this.
  3. Picbuster

    Well-Known Member

    Dec 2, 2013
    823
    101
    I do not understand what you try to do but:
    Vdd max =6.5V a car will carry relays hence V system could carry spikes of 60-100V but also negative going spikes.
    a shunt will work however the voltage over the shunt is radiometric. A load at pic's output pins will show up at the input and will force the voltage over the shunt down.
    An input filter is mandatory when dealing with dynamo's relays and other nasty spike producing things.

    Advice: use a Mic2940A or similar with an input filter to the car battery ( cap's, coil, resistor and TVS will do the job)

    Picbuster
     
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