Hello all!
Can anyone help me?
I have a question. when TL431 uses as a op-amp with reference voltage 2.5 to generate compensator type 2. why is mininum catode -anode voltage 2.5V?
thanks in advance!

 

you set the voltage using two resistors on the gate pin


datasheet

 

Have you looked at the datasheet? 2.5V is the reference voltage. As Dodgydave pointed out, you can make the cathode voltage higher with a voltage divider. See Fig. 20.
Dave incorrectly called the feedback pin "gate". It is actually the "ref" pin.
See the attached specs.

 

In SMPS we use TL431 as a error amplifier. The mininum catode-anode voltage is reach when TL431 is full ON (saturated). This voltage is in range between 1.8V ... 2.2V region. But in calculation we use 2.5V as worst case scenario.

 

Have you looked at the datasheet? 2.5V is the reference voltage. As Dodgydave pointed out, you can make the cathode voltage higher with a voltage divider. See Fig. 20.
Dave incorrectly called the feedback pin "gate". It is actually the "ref" pin.
See the attached specs.

Thank you for replying!
I wonder if catode-anode voltage can be under 2.5V. its value is output of error amplifier. I want to it as error amplifier.

 

Thank you.
It is true. its value is about 2V. I want to use to generate VAK when Vo changes.but VAK has only 2 values. it is 2V or the one Vo.
I attach circuit in file.