LB1405, 15-level display circuit application (b)

LB1405/1415 is a five-digit LED single display driver integrated circuit produced by Japan's Sanyo Company, using a dual in-line
16-pin package. The circuit is internally composed of an input amplifier, five voltage comparators and a voltage stabilizing circuit, as shown in Figure 4-50(a).
It can drive both AC and DC level meters and LEDs for level display. The circuit has internal The voltage stabilizing circuit has
a wide adaptability range to the power supply voltage of 4.4~12Vo. It uses a constant current drive method for the light-emitting diodes to avoid
the impact of changes in the power supply voltage on the light-emitting diode current. In addition
, the value of the comparison level and the response time of the light-emitting diode lighting and extinguishing can be changed by changing the value of the external resistor . The relevant parameters of LB1405 and LB1415 are shown in Table 4.
90
    The difference between LB1405 and LB1415 is that their internal voltage comparators are slightly different, so the definition of the OdB indication
is also different. The former refers to the level when the voltage of pin 2 is 2.37V, and the latter should be used when 1_5Vo Note that
the amplitude of the input signal must not be greater than V cc +0.3V, otherwise the integrated circuit will be damaged.
    Figure 4-50(b) and (c) are the application circuits of LB1405. This circuit uses two single display drive circuits to form a
two-channel display drive circuit. Two ICs can also be used to form a nine-segment level display circuit . See Figure 4-50 (d).
    LB1419 is a nine-bit level display driver integrated circuit. It contains a voltage amplifier, nine voltage comparators
, and two sets of voltage references. The first voltage reference is used by the internal voltage comparator as a comparison reference voltage, and the second reference
voltage is 4.7V, which is output from pin 16 and used as a bias voltage by an external current-stabilizing transistor.
    The power supply voltage range of LB1419 is 5_5~16V, the input voltage range is -0.3-vVoc, and the output conduction
voltage of pin 7~15 is 1,2Vo.
    Different from other drive circuits, LB1419 adopts series drive mode, with 9 light-emitting diodes each. 3 are connected in series to form
a group, and a transistor (or constant current tube) is used to provide a stable driving current. The bias current of the constant current transistor
is provided by the second reference voltage output by pin 16.
    The number of light-emitting diodes in each group of series N = (minimum supply voltage - constant current tube saturation voltage drop) increases the forward voltage drop of the photodiode
.
    When LB1419 performs logarithmic level display, the interval between each segment is 3 (Lu). When Vcc - 12V and the reference comparison voltage = 3V
, the corresponding comparison level of each output terminal is as shown in Appendix Table 4, 10 0