TL431 voltage regulator chip working process and quality detection

TL431 is a precise voltage regulator integrated device. Because TL431 has high control voltage accuracy and relatively small temperature coefficient, it can provide accurate reference voltage. This device can also be seen in switching circuits such as battery car chargers and induction cooker circuits. This kind of precision voltage reference integrated circuit is widely used. Now I would like to give my friends a brief introduction to this integrated circuit commonly known as a voltage regulator.

 

Introduction to TL431

This kind of integrated circuit has three forms, one is like a plastic-encapsulated triode, and its package form is T0-92A. It has three pins, with the plane facing itself, the first pin from the far left is represented by R, which is the voltage sampling pin; the second pin is represented by A, called the anode; the rightmost lead The foot is denoted by K, which is the control terminal.

The second type is in the form of integrated patch, and its package is SOJ-8 type, with eight pins, of which the second, third, fourth, fifth, and seventh pins are unused pins. The third is the patch shape, SOT-23 package form.

We use a circuit diagram to illustrate the working process of this TL431 voltage regulator chip, we can see from the figure that the output voltage can be adjusted arbitrarily from 2.5V (Verf) to 24V with two resistors RW and and R3.

1. The process of stabilizing voltage output through TL431

We assume that when the output voltage drops, the voltage at the R pin of the TL431 voltage regulator chip will decrease. This reduced voltage will increase the K pin (cathode) voltage of the TL431 after being amplified internally by the T1431, and then pass through the MOS After the tube K790 conducts conduction adjustment, the output voltage will increase.

We also assume that when the output voltage increases, the voltage at the R pin of the TL431 voltage regulator chip will also increase, and the voltage at the cathode K pin of the TL431 will decrease after the increased voltage is processed by the internal circuit of the TL431. The dynamic resistance of the MOS tube as a regulator tube will increase, which will cause the output voltage of this circuit to decrease.

2. Summary of the voltage stabilization process

Therefore, we can easily understand through the process of voltage stabilization that when the voltage of the reference electrode R of the TL431 increases, the voltage of the cathode K of the TL431 will decrease. On the contrary, when the voltage of the reference electrode R of the TL431 decreases, the voltage of the cathode K of the TL431 will decrease. The voltage of the cathode K of the TL431 will increase. It is through this voltage adjustment that the output voltage is stabilized.

TL431 voltage regulator chip's quality detection

The quality of TL431 can be measured with multimeter R×1kΩ. You can also use the diode gear of the digital multimeter to measure. The measurement steps are as follows.

The first step is: We first use the black test lead to test the anode A of the TL431, and the red test lead to test its reference electrode R. The number that should be displayed at this time is 1.4, and then the number displayed by the test pen should be 1.3.

The second step is: use the black test lead to test the anode A of the TL431, and the red test lead to test its cathode K. The number that should be displayed at this time is 1, and then change the test lead and the displayed number should be 0.6.

The third step is: use the red test lead to test the reference electrode R of the TL431, and the black test lead to test its cathode K. The number that should be displayed at this time is 0.7, and then change the test lead and the number displayed should be 1.

Another simpler method is to use the PNP socket in the hEF gear of the digital multimeter to test. We insert the reference electrode R of the TL431 into the "E" hole, the anode A into the "B" hole, and the cathode K into the "C" hole. At this time, the digital multimeter should display a value of approximately 431. If the displayed value is larger than this value, it means that the chip should be damaged. When the stabilized integrated chip is damaged, if there is no replacement of the same model, we can replace it with KA431, LM431, YL431, etc.