• State TI Thinks Resolved
  • Locked Locked
  • Replies 7 replies
  • Answers 3 answers
  • Subscribers 62 subscribers
  • Views 189 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

LM3914: LM3914: LM3914N-1/NOPB Part Replacement

LM3914: LM3914V

Ramana murthy
Expert 1640 points
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

Please suggest me the changes

Regards

  • 0
    TI__Mastermind 18550 points

    Hello Muruthy,

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

    Kind Regards,

    Liaqat

  • 0
    TI__Mastermind 18550 points

    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?

    Once I get your answers, I will respond quickly.

    Kind Regards,

    Liaqat

  • 0 in reply to Liaqat Khan
    Expert 1640 points

    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

  • 0 in reply to Ramana murthy
    TI__Mastermind 18550 points

    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

     

  • 0 in reply to Liaqat Khan
    TI__Mastermind 18550 points

    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

  • 0 in reply to Liaqat Khan
    Expert 1640 points

    Thanks for your warm reply

    Please let me the value of R5 for the Input voltage range of 18V - 25.2V.

  • 0 in reply to Ramana murthy
    TI__Mastermind 18550 points

    For 18V-25.2V, I am calculating the resistor R5 to be 23.2K ohm and calculation is as follows:

    For BAT+ of 18V, R2 will have a voltage of 0.873V. So R5 should have 0.873V when overall voltage across the whole divider ladder is 1.25V. Since sum of internal resistors is 10K ohm, R5 needs to be 23.2K to provide a divided voltage of 0.873 across it.

    Kind Regards,

    Liaqat