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Topic: Help with Lm3914 (Read 1 time) previous topic - next topic

friedlbasson

much appreciated!!

Regards, Freidl  :)

Wawa

#16
May 20, 2019, 10:53 am Last Edit: May 20, 2019, 10:55 am by Wawa
This online calculator might be useful to help you 'make' that 31k (31000 ohm) from two common resistors.
39k and 150k in parallel would be close.
Leo..

strak

Can anyone help me.
LM3914.

OK I get the program LED current as being approx 10 times current to 0V from pin 7 . Although this must consider current from pin 6 (Rhi ) to 0V too to be more accurate.

I get the pin7 to pin 8 is fixed by the IC at approx 1.25.

It`s the next bit that I struggle with - making the Rhi and Rlo voltages other than full supply voltage.

Am I right in thinking that if we make a potential divider R1 being on pins 8 to 7, R2 being on pins 7 to 8 and R3 being on pins 8 to 4 and finally R4 being on pins 4 to ground,

That would give us1.25V across R2 and setting (mostly) the LED current, the actual current across R2 would result in similar current thru R1, R3 & R4 thereby setting those voltages.

Then factor in the internal divider chain resistors to check it does not vary the voltages and also the LED current significantly.

My aim is to set an LED current at 10 or 15mA say.

Voltage comparisons across the divider chain to  start at 1.8V to 4.0V.

Or am I way off?

Thanks


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