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TL431: Using TL431 as regulated power supply

user4563649
Prodigy 30 points
Part Number: TL431
Other Parts Discussed in Thread: LM4040-N,

Using TL431 as regulated power supply，But now there is no-load output voltage instability, replacing the C1 （104 to 103）, stability effect is better,but there are still large fluctuations, I would like to ask whether there is a problem with this application circuit

  • 0
    TI__Mastermind 19550 points

    Hi,

    The TL431 has a instability region as specified on figure 16/18 of the TL431 datasheet. It is important to use a capacitor that is outside of this region.

    We have also made a app note to discuss this. If you need a low cost regulator for 2.5V that does not have a instability region, I would use the LM4040-N.

    If

  • 0 in reply to Marcoo Z
    Prodigy 30 points

    After reading the specification, I didn't understand it. Could you tell me more about it or say that there is something wrong with my application? Thank you!

  • 0 in reply to user4563649
    TI__Mastermind 19550 points

    I'll be glad to help explain more. The capacitor C1 is either 104 which is 100nF or 103 which is 10nF. Both values are in the unstable region of figure 16 of the datasheet. This means that the TL431 has a high tendency to be unstable and have oscillation and ripple. I would recommend to increase the capacitor value to 10uF and above  or 1nF and below for 2.5V at low IKA to ensure stable operation. Another option would be to use a TL431LI which is P2P and can use a 2.2uF cap and above instead of 10uF. Or if you are just using the TL431 to create a stable 2.5V reference, you can use a LM4040-N 2.5V which is stable for all capacitors including 103 and 104.