I am trying to control voltage range from 1.5 to 34 using LM338 voltage regulator with 1000u capacitor at the input 430u capacitor at the output with
potentiometer @ the adjustment terminal.

I have 37v and around 5 Amps current at the Vout but when i try to reduce the voltage using potentiometer,resistor 120 ohms burns out. Please suggest me how to control and get constant Voltage & Current.

 

You can get constant voltage or constant current, pick one, you can't control both at the same time.

Post the schematic of what you have.

 

Sounds like your 120 ohm pot is the constant current regulation resistor,better post your circuit for further assistance.

 

Here is my schematic for you reference i have both voltage and current , since we can't control both voltage & current
so i need to keep the voltage constant 32V and current should be adjustable.

 

Then you need to use it in current regulation mode,like the circuits in the datasheet, page 14 current regulation top two circuits


Note if you limit the current, the voltage will drop, You Cant Alter Both at the same time!


https://www.google.co.uk/url?sa=t&s...ghJMAs&usg=AFQjCNHEWtzZ05HcAXjFKsKPReQNeqL-VA

 

Hello,

You can never have a higher voltage on the output of the regulator.
There will be a dropout voltage of 1.5 to almost 3 volts depening on the drawn current:



Bertus