Light emitting diode display circuit one a

Light-emitting diodes can be driven by DC, AC and pulse. The typical display circuit of a resistor-stepped light-emitting diode is
shown in Figure 13-1.
    The current-limiting resistor R in the LED circuit can be calculated according to the following formula;
    ① When driven by DC [see Figure 13-1 (a), (b)],
    R=EU, P≥21FR,
where R-current-limiting resistor , kn;
    E-power supply voltage, V;
    UF-light-emitting diode forward voltage drop (1.7-2V), V;
    IF-light-emitting diode operating current, generally 1/3-1/5 of the maximum
    operating current IFm, mA;
    Pr is the power of the selected resistor, and the actual power consumption is
    Wei R. To prevent the resistor from overheating, sufficient
    margin .
    ② When driven by AC [see Figure 13-1 (c), (d)],
    R=0 45U—UF
    IF
formula where U-effective value of AC voltage, V.
    The diode VD is used to protect the light-emitting diode
from breakdown during the negative half cycle of AC . 1N4007, 1A/1000V can be selected.
    ③ When driven by pulse [see figure (e)],
    R=E2 (Uces+UF)
    fF
in the formula B - power supply voltage, V;
    U. . . ——The tube voltage drop when the triode is in saturated conduction (about 0. 3V), V.