Originally Posted by audioguru

The LM317 needs a minimum of a 10mA load or a 120 ohm resistor between ADJ and output or its output voltage will rise on some of them. Then the resistor from ADJ to ground will need re-calculation.

Thanks, The problem was that.

Originally Posted by audioguru

The LM317 needs a minimum of a 10mA load or a 120 ohm resistor between ADJ and output or its output voltage will rise on some of them. Then the resistor from ADJ to ground will need re-calculation.

Dear Audioguru,
I read the datasheet of LM317. But I can't figure out how you undrestood the resistor between Adj and output should be 120ohm. Could you please explain it for me? It would be a good experience for me.

Originally Posted by Fahime

Dear Audioguru,
I read the datasheet of LM317. But I can't figure out how you undrestood the resistor between Adj and output should be 120ohm. Could you please explain it for me? It would be a good experience for me.

The datasheet specifies "a minimum load current". Without a load then the current in R1 and R2 sets the minimum load current.

Many people see the schematic on the first page of the datasheet with the 240 ohm resistor for R1 but don't notice that the IC is the more expensive LM117 with half the minimum load current of the less expensive LM317.

The minimum load current is spec'd with a Vin - Vout voltage of 40V and is less with less voltage but it doesn't cost any more to make R1 always 120 ohms with an LM317.

Originally Posted by audioguru

The datasheet specifies "a minimum load current". Without a load then the current in R1 and R2 sets the minimum load current.

Many people see the schematic on the first page of the datasheet with the 240 ohm resistor for R1 but don't notice that the IC is the more expensive LM117 with half the minimum load current of the less expensive LM317.

The minimum load current is spec'd with a Vin - Vout voltage of 40V and is less with less voltage but it doesn't cost any more to make R1 always 120 ohms with an LM317.

Thanks alot. It was really helpful.

Originally Posted by audioguru

Many people see the schematic on the first page of the datasheet with the 240 ohm resistor for R1 but don't notice that the IC is the more expensive LM117 with half the minimum load current of the less expensive LM317.

Which really annoys me, they shoud change the datasheet to show a 120hm: resistor!