The reference pin of the power feedback circuit TL431 is not 2.5V, how to adjust it?

Knight97538

The reference pin of the power feedback circuit TL431 is not 2.5V, how to adjust it? [Copy link]

 

The reference pin of the power feedback circuit TL431 is not 2.5V, how to adjust it?

maychang

[The reference pin of the power feedback circuit TL431 is not 2.5V, how to fix it]

According to your circuit, the reference pin of TL431 cannot be 2.5V, but the voltage obtained by dividing 8V by two resistors Rfbu and Rfbb.

maychang

To make the TL431 reference pin 2.5V, the voltage of pin 3 of TL431 should be fed back to the reference pin.

maychang

On the left side of the picture is UC3842, which is a commonly used single-ended flyback switching power supply control chip. This type of single-ended flyback switching power supply often uses the optocoupler isolation transformer primary and secondary circuits in the figure. TL431 is also often used as a voltage reference. I am afraid you copied the typical application circuit incorrectly. Take a closer look.

maychang

As mentioned above, the reference pin voltage of TL431 is the voltage obtained by dividing the 8V by two resistors Rfbu and Rfbb. If the reference pin voltage of TL431 is not 2.5V, you should first check whether the 8V voltage is accurate.

huo_hu

The right side doesn't need to be so complicated, just use a resistor to limit the current, not to mention 8V, 200V is no problem

431 without pressure division is 2.5

led2015

In circuit design, TL431 is often used to make a 2.5V reference voltage, which is equivalent to a 2.5V voltage regulator.

qwqwqw2088

If there is a problem with the circuit, it will generally be lower than 2.5V

zhangxm666666

The reference pin of the power feedback circuit TL431 is not 2.5V. How to adjust it? Just adjust it according to this formula: V-TL431 reference pin voltage V=(Rfbb/(Rfbu+Rfbb))*8. After deduction, adjust Rfbb until you are satisfied.

Knight97538

zhangxm666666 posted on 2023-5-12 11:31 The reference pin of the power feedback circuit TL431 is not 2.5V. How to adjust it? According to this formula, it can be adjusted. V-TL431 reference pin voltage V=(Rfbb/(Rfbu+Rfb ...

Adjust Rfbb until you are satisfied

Where can I find this formula?

yyq006

The resistance of the feedback circuit is fine. Check the circuit diagram carefully. If the circuit is fine, there may be a problem with the welding, especially the welding of 431.

lkh747566933

To make the TL431 reference pin 2.5V, the voltage of pin 3 of TL431 should be fed back to the reference pin.

Knight97538

lkh747566933 posted on 2023-6-29 00:47 To make the TL431 reference pin 2.5V, the voltage of pin 3 of TL431 should be fed back to the reference pin.

How can I feed back the voltage of pin 3 of TL431 to the reference pin?