How is this adjustable if it uses fixed values? LM2673

[CluQu]

I recently got an LM2673 Adjustable Voltage Regulator for a new more beefy power supply. However when I look at the datasheet under the Adjustable configuration, not the fixed output configuration, it clearly uses two fixed values for R1 & R2. Below I will attach the link to Texas Instruments and the datasheet. I'm not seeing how fixed values gives an adjustable value... Anyone that has worked with this IC or some related voltage regulator that could explain would be most appreciated.

http://www.ti.com/lit/ds/symlink/lm2673.pdf

 

[john monks]

You have to add external resistors to your feedback to make the power supply adjustable. Look at the example schematic below the block diagram.

 

[Harald Kapp]

Adjustable means that the output voltage of the regulator is settable by using the suitable resistor combination. If you use a potentiometer instead of the resistors, it will be truly adjustable.

The nomer "adjustable" is used mainly to distinguish this kind of regulator from fixed voltage regulators which don't allow setting or adjusting the voltage.

 

[davenn]

I'm not seeing how fixed values gives an adjustable value... Anyone that has worked with this IC or some related voltage regulator that could explain would be most appreciated.

because when they say adjustable it means you can vary its normal fixed output to some other fixed voltage using different values for R1, R2

whether you can replace one of those fixed resistors with a trimpot go give a variable range , I'm not sure. Quite possibly.
If you are really wanting a wide range variable supply for benchtop testing, I suggest you look at regulators that are designed to be continuously adjustable. eg a LM 338 etc

cheers
Dave