LM3915 datasheet(13/25 Pages) NSC

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Giải thích chi tiết về linh kiện	Dot/Bar Display Driver

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Application Hints (Continued)

the LED current will be at least 5 mA. R1 will typically be

between 1 k

Ω and2kΩ. To trim the reference voltage, vary

R2.

The circuit in Figure 8 shows how to add a LED intensity

control which can vary LED current from 9 mA to 28 mA. The

reference adjustment has some effect on LED intensity but

the reverse is not true.

Multiple LM3915s

Figure 9 shows how to obtain a common reference trim and

intensity control for two LM3915s. The two ICs may be

connected in cascade for a 60 dB display or may be handling

separate channels for stereo. This technique can be ex-

tended for larger numbers of LM3915s by varying the values

of R1, R2 and R3 in inverse proportion to the number of

devices tied in. The ICs’ internal references track within

100 mV so that worst case error from chip to chip is only

0.1 dB for V

REF = 10V.

00510415

FIGURE 7. Design Equations for Fixed LED Intensity

LM3915 bảng dữ liệu(PDF) 13 Page - National Semiconductor (TI)