poobah said:Right... the "new" resistor is what drops the voltage down to your desired regulated voltage.
In order to calculate the 3rd resistor, you need to know your max and min load current... and the raw voltage, and the regulated voltage.
if all I need is resistor to drop the voltage, then what is the purpose of the TL431 circuit? is it to keep the output voltage constant?
Hi jarthel,
You are correct that the TL431 keeps the voltage constant. Basically it does this by either drawing more or less current to keep the voltage that it uses for comparison equal to it's own intenal 2.5V reference.
By drawing more or less current there will be a corresponding change in voltage drop across the '3rd resistor'.
There is a good article about this at tubecad.com, see the following PDF:
TubeCad Journal Shunt Regulator
Happy building
You are correct that the TL431 keeps the voltage constant. Basically it does this by either drawing more or less current to keep the voltage that it uses for comparison equal to it's own intenal 2.5V reference.
By drawing more or less current there will be a corresponding change in voltage drop across the '3rd resistor'.
There is a good article about this at tubecad.com, see the following PDF:
TubeCad Journal Shunt Regulator
Happy building
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