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Beginners / Re: LM317: divider values and minimum load current
« Last post by pope on Today at 03:50:36 pm »In other words, if the actual load is 15mA or 150mA or 1.5A, does it matter whether R1 is 120R or 360R or anything in-between?
If you have a load with a guaranteed draw of >10mA then you can use higher values for the divider resistor. However, the other factor you have to look at is IADJ or the current on the adjust pin. The TI datasheet for a regular LM317 shows this to be as much as 100µA with a variation due to load or voltage changes of up to 5µA. With 360R for R1, you'll have 3.3mA and that 100µA would represent 3% of the divider current and thus a proportionate error. The typical IADJ current and variation thereof are much lower, so that 3% would be the worst-case. For production you have to worry about worst case, for something one-off or low volume that you can 100% test then you could probably use 1k for R1 and still be fine.
Thank you for the detailed explanation but unfortunately due to my luck of English skills I'm having a bit difficult time to understand wht you mean.
In simpler terms, using 360R is OK or not really? And if so, would the suggested 240R is better?
I'm straugglin to understand this "With 360R for R1, you'll have 3.3mA and that 100µA would represent 3% of the divider current and thus a proportionate error. The typical IADJ current and variation thereof are much lower, so that 3% would be the worst-case. "