LM3914: LEDs not dimming

Hi Tyler,

Thanks for your question. I cannot see the picture you have posted. Can you try posting it again?

Best,

Grant

7444.LM3914 schematic - Jul 29 2020 - 12-02 PM.pdf

I apologize, I couldn't figure out how to insert an image.  I hope you can get it in the link above.

Hi Tyler,

Yes, I can see the image in the .pdf. Please give me some time to review it and come up with an answer for you.

Best,

Grant

Hi Tyler,

When you say that you need to be able dim the LEDs, do you intend to dim them by manually adjusting the resistor connected to REFOUT (pin 7)? or did you have some other mechanism in mind?

I do see the drawing you attached but it is hard to follow because it not a schematics. In order not to miss any wrong connectivity during review, is it possible to hand draw a schematics like the one below?

Kind Regards,

Liaqat

Hello Tyler,

I wanted to follow up since I did not get any further response on this. Can you please let me know how you are trying to dim the LEDs? LED current, hence dimming, is fixed based on how much current is flowing out of refout pin and that is dependent on the value of resistive load connected to this refout pin. So I would like to know how you are dynamically trying to adjust the refout current?

Kind Regards,

Liaqat

Hi Liaqat,

Thank you for responding to my question.  I have a 20k ohm variable resistor connected to the ref out pin which then goes to the negative rail on my board and I am trying to dim the LEDs by increasing the resistance of that resistor.  Thanks again.

Sincerely,

Tyler

Hi Tyler,

Your circuit diagram that you had attached previously shows 100K fixed resistor in series with the 20K variable resistor that you are changing to try to change LED brightness. I think that 100K fixed resistor is swamping the 20K variable resistor so that you don't see any variation in LED brightness. If you can remove this 100K series resistor and just keep the 20K variable resistor, you should see brightness change as you vary the resistor from 20K (LED current of ~0.6mA) to say 1K (LED current of ~ 12.5mA).

Kind Regards,

Liaqat

Hi Tyler,

Did my suggestions not resolve the issue of not being able to dim the LEDs by varying load resistor at refout pin? If correct, can you please provide a more complete schematics of your circuit and I will be happy to review it to see if I can spot some other possible issue with your design?

Kind Regards,

Liaqat

Thanks again for your response.  Your answer did not help yet.  I found that my drawing is not accurate.  I will try to make a new drawing that is more professional.

Hello,

Thank you and I Iook forward to getting and reviewing your schematics to see if I can spot the issue.

Kind Regards,

Liaqat