delabs Circuits

Wednesday, June 01, 2016

LM3914 meter for 25 V DC

"I wish to assemble a bargraph display to indicate approximately 25volts dc.How many LM3914 I should cascade? How to calculate resistor value which is grounded from the junction of Pin 6 & 7 (Rhi &Ref.out)? Assuming i need to cascade 3 LM3914s,what is the method to cascade these ics? The display need not be precise or very bright. I hope you can help me out."

Mains Voltage monitor using LM3914

"I shall be very grateful. Can we do it in such a way that the first LM3914 displays 1-10 v & second 11-20v & the third 21-30v?"

Thank you again - Mail from AD

Reply from delabs

Have a look at the TI application note which has many examples. Understanding this will help you make your own solution.

LM3914 - Dot/Bar Display Driver

20-Segment Meter with Mode Switch

20-Segment Meter with Mode Switch

Analog and 3-1/2 digital display

Cascading is required if you want more resolution. Example for measuring 20V, you want to show in 1V per LED steps. It can withstand +/- 35 Volts input upper limit.

The inbuilt reference is 1.2V use it as shown in the Typical Application. This also helps in setting the brightness of LED display. You may need to use external attenuators, buffers or precision  rectifiers to measure AC voltages or High Level DC voltages.