TL431 shunt capacitor

Zener diode in the circuit work, it will produce an irregular periodic noise, this irregular noise is called Zener noise.

Although the zener noise level is not high, but it is one of the important factors that affect the output characteristics of the zener diode. In order to reduce the output voltage of the zener diode, a capacitor can be used in parallel with the zener diode so that the shunt capacitor can absorb the Zener noise of the zener diode to improve the output characteristics of the zener diode.

In addition, the parallel capacitor in the Zener diode can also absorb the power supply ripple, making the output voltage regulator diode more stable.

Second, when a zener diode is used in parallel with a capacitor, the settling time of the zener diode output voltage increases due to the charging of the capacitor, causing the output voltage to rise slowly. However, this is only an instantaneous power-on situation. During normal operation, the output voltage of the Zener diode is completely stable.

The advantage of using this method is that when the power supply is turned on, the output voltage of the zener diode will not overshoot. At the same time, it also plays a certain power-on delay and improves the transient characteristics.

Since there are so many benefits of zener diode and capacitor paralleling, and the use of the TL431 is very similar to the use of Zener diodes, the TL431 can be used in parallel with capacitors, and the TL431 also has many benefits when used in parallel with capacitors. However, when the TL431 is connected in parallel with the capacitor, the capacity of the TL431 is not suitable. Sometimes, the TL431 may not only work well, but will oscillate. This is because the current flowing through the TL431 has a certain relationship with the capacity of the capacitor.

Experiments show that if the capacitance of 0.01 ~ 3μF in parallel with the TL431 on the TL431 is likely to make TL431 oscillation, so TL431 parallel with the capacitor should be used in parallel TL431 capacitor value should be greater than 3μF or less than 0.01μF, This must be noticed.

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Author：Brittany Antonia （The author of article owns the copyright.）