LM3915

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SNVS740C – JANUARY 2000 – REVISED MARCH 2013

D1, D2: 1N914 or 1N4148

Figure 19. Precision Full-Wave Average Detector

D1, D2, D3, D4: 1N914 or 1N4148

Figure 20. Precision Full-Wave Peak Detector

CASCADING THE LM3915

To display signals of 60 dB or 90 dB dynamic range, multiple LM3915s can be easily cascaded. Alternatively, it is

possible to cascade an LM3915 with LM3914s for a log/linear display or with an LM3916 to get an extended

range VU meter.

A simple, low cost approach to cascading two LM3915s is to set the reference voltages of the two chips 30 dB

apart as in Figure 21. Potentiometer R1 is used to adjust the full scale voltage of LM3915 #1 to 316 mV

nominally while the second IC's reference is set at 10V by R4. The drawback of this method is that the threshold

of LED #1 is only 14 mV and, since the LM3915 can have an offset voltage as high as 10 mV, large errors can

occur. This technique is not recommended for 60 dB displays requiring good accuracy at the first few display

thresholds.

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