Voltage regulator

[gjoo]

I am trying to understand the voltage regulator(lm2941t)in this circuit. I do not understand why they chose those values for r2 and r3 and what vsense does in this circuit. Also, why is 22 uf needed on the input, when the data sheet only calls for .47 uf.

 

[gjoo]

Just one last question, is R1 even necessary and why did they choose a 1k resistor?

 

[Nigel Goodwin]

Just one last question, is R1 even necessary and why did they choose a 1k resistor?

Because R1 is the bottom half of a potential divider, the top half been the digital pot, wired as a variable resistor. The value will have been chosen to suit the value of the pot, and the voltage range required from the regulator.

 

[gjoo]

Oh, got it. Thank you

 

[tumbleweed]

This will give a maximum output voltage of 9V.

... and exceed the max voltage of the digital pot resistive section letting out all the magic smoke (Va, Vb, Vw max voltage = VDD, VDD max = 5.5V)

I'm not a fan of circuits that have a self-destruct mode.

There are some digital pots that can handle higher voltages, but I don't know if Microchip makes them or not.