TL431 application issue need your expert help!

[samuelzhao]

Dear every expert,

In an application, TL431AC is used as a 2.5V voltage reference. In this application, if parallel a capacitor at the Vout (intend to stable the voltage and decrease the noise, which is a common usage in a power supply), the output oscillation. why will the capacitor influence the output, could you please give me a detail and mathematic analysis? Thank you!

Please see the attachment for detail. Thank you!

Samuel

 

[Nigel Goodwin]

In an application, TL431AC is used as a 2.5V voltage reference. In this application, if parallel a capacitor at the Vout (intend to stable the voltage and decrease the noise, which is a common usage in a power supply), the output oscillation. why will the capacitor influence the output, could you please give me a detail and mathematic analysis? Thank you!

Have you ever heard of a 'neon relaxation oscillator'? - it works in the same way, you shouldn't fit a capacitor across the TL341 as it forms a relaxation oscillator.

 

[Roff]

TL431 is unstable under certain conditions of voltage, load current, and capacitive loading. The charts below are from Texas Instruments' **broken link removed**. They show the conditions that you must avoid.

 

[samuelzhao]

thanks!

Thank you very much, two experts!

Samuel