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LM217 voltage regulator question

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Chris Wilson:
I was looking for around 6 to 7V out from 12V in and I had a 5k ten turn pot to hand. using a cadence resistor box I found R1 at 1k gave a nice adjustment range but the spec sheets cite R1 as usually being a lot lower resistance, circa 240 Ohms. Is there anything bad in using 1k for R1 in the divider? Thanks.

Wimberleytech:
In order for it to regulate properly, the datasheet says it needs a minimum of 10mA (worst case, with 3.5mA typical) of load current.  A resistor of 125 ohms or lower guarantees that without any additional load.  If you use 1k, then you will need to be sure that you are always sinking additional current to meet the minimum load current specification.

magic:
My datasheet (ST) specifies 5mA worst case and that's where the 240Ω comes from.

Wimberleytech:

--- Quote from: magic on May 19, 2019, 11:27:24 pm ---My datasheet (ST) specifies 5mA worst case and that's where the 240Ω comes from.

--- End quote ---

Correct.  I was looking at a TI datasheet (actually for the 317).

Chris Wilson:
Thanks for the very fast replies! Will an HEF4013 flip flop (which it is powering) draw that much all the time or do i need to redesign the divider? It *SEEMS* to work OK on the breadboard...

EDIT, hmm it seems the HEF4913 only draws Ua levels maybe I need to change this :(

IDD supply current all valid input
combinations;
IO = 0 A
5 V - 1.0 - 1.0 - 30 - 30 uA
10 V - 2.0 - 2.0 - 60 - 60 uA
15 V - 4.0 - 4.0 - 120 - 120 uA

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