How to check TL431?

Как проверить TL431

Microchip TL431 is a three-terminal adjustable shunt regulator. It often can be found in PC power supply, etc. There can be a great deal of trouble if it breaks, for example there could be glitches in the motherboard performance and others. If there is a suspicion in a component failure, it should be changed right away. But how to check TL431 if there is nothing in touch for substitution and operational inspection is needed? For such task procedure hopefully this article will be of service.

How to check TL431 by multimeter?

Many a man, who face microchip TL431 for the first time, often say it is transistor TL431 thus try to check it with multimeter.

It doesn’t do any good because resistance between output terminals is different from one instance to another and vary in different details. To make the correct check of microchip TL431, it should be plugged into very simple circuit.

How to check TL431?

The resistor R3 is selected to meet the following requirement: the led functional current should not to exceed 20 мА. Resistances R2 and R3 are balancing resistors. They will influence at which voltage of powersupply led will light up. TL431 will open only if voltage on it’s gate terminal reach 2,5 V.

How to check TL431

Connected into such circuit TL431 is a perfect detector of overvoltage. Since source voltage is fixed – 5 V, microchip manipulation will be performed by trimmer resistor R2.





For vivid test, this circuit is implemented on development board, but if there is a need in a frequent check of such microchip, the circuit can easily be set in a small case and you get useful device. In initial state led doesn’t light up, TL431 is closed.

How to check TL431

Next, the resistance of trimmer resistor should be changed until microchip is open. Led lights up brightly immediately, there is no transitional moment or glimmering.

How to check TL431

This circuit can easily be used as the battery charge indicator or other voltage increase detector. Thereon TL431 check is over, microchip is functioning correctly and so it is completely operational.

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