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# LM3914: LM3914V

Part Number: LM3914

Dear Sir,

LM3914V
I am looking for resistor values, which is required for below two combinations

Requirement 1:
VoltageTI R&D.pdf Variation: 21V DC to 25.2 V DC

Requirement 2:
Voltage Variation:18V DC to 25.2 V DC

With Existing Schematic, I am getting this variation range.
16V DC to 26 V DC

Also, I want to control the brightness of the LED

Regards

• Hello Muruthy,

Thank you for your post. Please let me  review it and provide feedback in the next couple of days.

Kind Regards,

Liaqat

• Hello Muruthy,

Thank you for your patience. I am just getting back to your post and wanted to to ask what you meant by voltage variation? As I see in your schematics, RHI pin is connected to REFOUT pin which means that it will be at 1.25V reference voltage generated by internal reference. So the input signal will need to be within the 1.25V range for the bar display to change incrementally. So I am not sure if I understand what you mean by "voltage variation of 21V DC to 25.2V DC"

Can you please clarify? Also, what voltage is BAT+ at?

Kind Regards,

Liaqat

• Sir,

All LEDs should be ON at 25.2 VDC
All LEDs Should be off at 21.0 VDC

BAT+ Variable voltage is feeding at this Pin

• Hello Murthy,

Thank you for the clarification. Reviewing the datasheet, it seems that LM3914 can support your application requirements of bar graph for 21V to 25V as absolute maximum for V+ supply for LM3914 in the datasheet is 25V and the input signal buffer swing is also limited to 12V. So it appears that achieving a bar graph for input voltage of 21V-25V is not possible directly and you will first need to scale the input voltage down to so that the maximum is below 12V. Once maximum is below 12V, you can use equation in the :internal voltage reference" section of the datasheet to determine appropriate values for R1 and R2.

Kind Regards,

Liaqat

• My apology as I totally missed that you have already scaled down the input voltage range by the voltage divider formed by R2 and R1 in your schematics. With this voltage divider and input voltage range of 21V - 25.2V, I think a R5 value of 44K in your schematics should achieve the desired bar display to cover this input voltage range evenly.

Kind Regards,

Liaqat