The simplified LM3914 block diagram is to give the general idea of the circuit's operation. A high input
impedance buffer operates with signals from ground to 12V, and is protected against reverse and overvoltage
signals. The signal is then applied to a series of 10 comparators; each of which is biased to a different
comparison level by the resistor string.
In the example illustrated, the resistor string is connected to the internal 1.25V reference voltage. In this case, for
each 125mV that the input signal increases, a comparator will switch on another indicating LED. This resistor
divider can be connected between any 2 voltages, providing that they are 1.5V below V+ and no less than V−. If
an expanded scale meter display is desired, the total divider voltage can be as little as 200mV. Expanded-scale
meter displays are more accurate and the segments light uniformly only if bar mode is used. At 50mV or more
per step, dot mode is usable.