TLV431 problem

Discussion in 'General Electronics Chat' started by Dritech, Jun 12, 2014.

  1. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,

    I am using the TLV431 shunt regulator. With the output I connected a potentiometer with a resistance of 500 to 400 ohms. When using the Excel calculator provided by Texas Instruments, I came with the following resistor values:

    R1 = 8.7 ohms
    R2 = 35700 ohms
    R3 = 12400 ohms

    (Note: Input voltage = 4.9V to 5.1V , output voltage = 4.8V)

    Calculator Link:

    http://www.ti.com/tool/tl431calc

    When connecting the circuit to a power supply, the SC indication LED was turning on. I then increased the value of R1 to approx 1kohms (If I remember correctly). This time there were no short circuits.

    I then did the following calculations to determine the value of R1:

    Vout = 4.8V therefore 4.8V / 400ohms = 12mA

    R1 = (Minimum input voltage - output voltage ) / (output current + 1mA for TLV431 saturation)

    R1 = (4.9V - 4.8V) / (12mA + 1mA)

    R1 = 8 ohms

    8ohms is very close to the one provided by TI calculator, so what is causing this short circuit please?

    Any help would be highly appreciated.
     
  2. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    What short circuit?
     
  3. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    With 8.7 ohms as R1, the benchtop power supply was indicating a short circuit (SC led). The current consumed was also maximum.
     
  4. crutschow

    Expert

    Mar 14, 2008
    13,052
    3,244
    Post your circuit diagram.
     
  5. ronv

    AAC Fanatic!

    Nov 12, 2008
    3,292
    1,255
    Your divider for the reference pin is wrong. You want that point to be 2.5 volts at your desired output voltage.
     
  6. Dritech

    Thread Starter Well-Known Member

    Sep 21, 2011
    756
    5
    Hi,

    Thanks for the reply. That shunt regulator is the TLV431 not the TL431.
     
  7. pilko

    Senior Member

    Dec 8, 2008
    213
    20
    "Note: The 35Kohms resistor is formed from a 22Kohms fixed resistor and a 20K trimmer in parallel"
    Your parallel combo is 10.5K max.
     
  8. Alec_t

    AAC Fanatic!

    Sep 17, 2013
    5,809
    1,105
    They should be in series, not parallel.
     
Loading...