Hello I have an LM7812CT power regulator and I want to use it to convert a 28V dc to a 12V dc.
I am using the circuit provided in the data-sheet using 2 capacitors, one 0.33uF connected to the input voltage pin(1)and the ground ,and one 0.1uF connected to the ground and the output pin(3).
My problem is that I get output voltage 3.9-4.0 Volts.
I get this value even with 12V supply to input.
How can i fix it to get my 12V?
Where do you think am I wrong?
Is it burned??
Any ideas welcome
edit:: ok guys the LM7812ct was burned after all. I replaced it and everything worked ok!!
thnx and keep up the good work
Best Answer
I don't know how you burned the 7812; it has both short-circuit and thermal overload protection.
Anyway, you have 16 V input-output difference, and that's a lot. A 60 mA load will already cause 1 W dissipation. I would suggest to place a power resistor in series with the 28 V to decrease the 7812's voltage drop. You can afford at least 10 V across the resistor, so if you want 1 A output you need a 10 Ω/ 10 W resistor. The 7812 still will dissipate 6 W then, so will need a considerable heatsink.