LM350 Voltage Regulator Resistor Loads

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BarryBozeman

Joined Apr 1, 2016
41
Hi there -

I have a handful of LM350s, looking to create a variable voltage source - 9v to 0v (or wherever the Reference Voltage can safely be set - 1.25v?). The basic diagram, from the datasheet, is included here.

I'm a little uncertain about picking resistor values, however. At the moment, I only have 100k pots for R2. The datasheet suggests 240 ohms for R1. I'm pretty sure that would be a bad pairing. Is it possible to use a different value for R1 to match my 100k pot? Or do I need to do something to restrict the pot?
 

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dl324

Joined Mar 30, 2015
12,786
Without a negative voltage, the lowest output voltage is 1.2-1.3V.

The datasheet states a minimum load current of 10mA, so R1 should be more like 120 ohms. You can use a 100k pot (1k would be more appropriate with R1=120 ohms), but a smaller pot would give more adjustment accuracy; maximum output voltage will be determined by input voltage and the value of the program resistor (R1).

EDIT: Added "adjustment" above for clarification.
 
Last edited:

crutschow

Joined Mar 14, 2008
26,974
For 9V output the pot should be no more than 1kΩ (which would give a maximum output of about 11V) for a good adjustment range and resolution with a 120Ω resistor for R1.
 
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