VREF=1.25V×(1+R2R1)cap V sub cap R cap E cap F end-sub equals 1.25 cap V cross open paren 1 plus the fraction with numerator cap R 2 and denominator cap R 1 end-fraction close paren : Connected between Pin 7 (REF OUT) and Pin 8 (REF ADJ). : Connected between Pin 8 (REF ADJ) and Ground. Step 2: Calculate LED Current ( ILEDcap I sub cap L cap E cap D end-sub The current flowing out of Pin 7 ( IREFcap I sub cap R cap E cap F end-sub
) is roughly 1/10th of the current that will flow through each LED.
This guide provides an updated look at calculating the critical resistor values for the LM3915 to ensure your LED display is perfectly calibrated for both brightness and voltage range. 1. Key Formulas for Circuit Calibration lm3915 calculator updated
Data sourced from instructional guides at Instructables and SparkFun . 3. Critical Component Selection Tips : It is highly recommended to keep VLEDcap V sub cap L cap E cap D end-sub
resistor in series with the signal input (Pin 5) can protect it up to ±100Vplus or minus 100 cap V : Always place a tantalum or VREF=1
below . If your supply is higher (e.g., 12V), use a dropping resistor in series with the LEDs to prevent the IC from overheating, especially in Bar Mode. Mode Selection (Pin 9) : Bar Mode : Connect Pin 9 directly to Pin 3 ( Dot Mode : Leave Pin 9 floating (open circuit). Input Protection : While the IC can withstand ±35Vplus or minus 35 cap V , adding a
ILED≈12.5R1cap I sub cap L cap E cap D end-sub is approximately equal to the fraction with numerator 12.5 and denominator cap R 1 end-fraction For a standard LED current of , should be approximately . If you need brighter LEDs (e.g., 20mA ), reduce to . 2. Practical Design Examples This guide provides an updated look at calculating
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