Utilize lm317 bandgap reference with minimal current?

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
Good Day,

How can I use the internal bandgap reference of a lm317 as an input for a comparator using the least current possible?

Currently I am using the voltage regulator configuration of the lm317 to provide 1.4v at out as seen in the attached image but this requires a load resistor which draws a significant amount of current (~1ma) for stability.

I found one post that said to ground the adjust terminal and take the reference at out but this gives me a voltage of VCC - .7

Thanks :)
 

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dl324

Joined Mar 30, 2015
12,871
How can I use the internal bandgap reference of a lm317
You can't because there doesn't seem to be one.
clipimage.jpg
Currently I am using the voltage regulator configuration of the lm317 to provide 1.4v at out as seen in the attached image but this requires a load resistor which draws a significant amount of current (~1ma) for stability.
LM317 aren't guaranteed to work with less than 10mA for the load plus reference current.
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
You can't because there doesn't seem to be one.
View attachment 229990
LM317 aren't guaranteed to work with less than 10mA for the load plus reference current.
I'm pretty sure this is, I have seen an internal diagram that indicated the reference part of the circuit.. I'll try to locate it

I could be mistaken but then how does the chip establish a temperature independent reference?
 

Thread Starter

k1ng 1337

Joined Sep 11, 2020
85
I'm pretty sure this is, I have seen an internal diagram that indicated the reference part of the circuit.. I'll try to locate it

I could be mistaken but then how does the chip establish a temperature independent reference?
Furthermore the lm317 reference is a nominal 1.25 which corresponds to the bandgap of silicon.
 

crutschow

Joined Mar 14, 2008
27,188
I found one post that said to ground the adjust terminal and take the reference at out but this gives me a voltage of VCC - .7
You need to load the output with at least 10mA (120Ω).

If you need a low current reference than use one of the low power shunt bandgap references,
For example the MAX6007B will operate down to 1μA.
 
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