TL431 application issue need your expert help! - Electronic Circuits Projects Diagrams Free

samuelzhao · 2nd September 2004, 08:54 AM

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** · 2nd September 2004, 10:53 AM

Quote:

Originally Posted by samuelzhao

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 · 2nd September 2004, 02:28 PM

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

samuelzhao · 3rd September 2004, 03:44 AM

Thank you very much, two experts!

Samuel

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3rd September 2004, 03:44 AM	(permalink)
samuelzhao	thanks! Thank you very much, two experts! Samuel