This is a circuit for a logarithmic scale LED bar display driver. AN6884 accept wide range of supply voltage, ranging from 3.5V to 16V. This VU (voltage unit) bar display circuit provides only 5 levels, but will accept wide range of input level because the scale is logarithmic: -10, -5, 0, 3, and 6dB points. The output current for each LED will be constant at 15mA, suitable for most LED types. This is the figure of the circuit;
To operate at voltage higher than 6V, a current limiting resistor R should be inserted between Vcc and the LEDs anodes, and the values should be chosen as shown in the table for appropriate power supply voltage and maximum operating temperature. This circuit is suitable for monitoring audio level of your amplifier’s output. If you need only to measure DC voltage level then the 2.2uF electrolytic capacitor can be omitted. [Circuit's diagram source: Panasonic Application Notes]
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