Ok, let’s see the next example circuit and this is called an undervoltage protection. We’ve seen something similar on the battery charger circuit where the IC will stop the charging process if the voltage was above 4.2V. But in this case, we want to turn off the output if the voltage is below a certain voltage. We will use this circuit and the cutoff voltage is equal to 2.5V multiplied by 1 plus the ratio between the two resistors of the voltage divider. For example, with 2k and 1K, the cutoff voltage would be 7.5V. When the input is below that voltage, the TL431 will power off the transistor gate so the load is not powered.

I mount this circuit on my breadboard using an IRF4905 MOSFET. I connect a load at the output and supply the circuit at 3V but the load is still OFF. I start increasing the input voltage and as you can see, while the input is below 7.5V the current value is 0 because the ouput is OFF. I get above 7.5V, as you can see, the load is now powered on. And if I get back to below 7.5V, the load is once again OFF. That’s how you can make an undervoltage protection circuit. You also have the circuit from the previous video for the battery balancer which is pretty much the same.

So as you can see you can use the TL431 as a undervoltage protection control when the load is on or off. I hope you like this tutorial and maybe you have learned something new. If my videos help you, consider supporting my work on my PATREON or a donation on my PayPal. Thanks again and see you later guys.