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Common Anode Super Bright Led
Driver Circuit
Driving common anode 7 segments led is easy, by
providing low logic input data (a - g), and provide positive voltage to the
common. as can be seen in Figure 1.
Figure 1. Simple 7 segments common anode led driver
Figure 1 can be applied easily, if the LED 7 segment requires a voltage about 5
volts. So that the PNP transistor, can be easily to drive 7 segment LED
multiplexing controls, because if the control voltage is 0 volts, then the LED
will be switched on, otherwise if
control voltage is 5 volts, then the LED will be switched off.
However, if 7 segments LED type is super bright, then the supply voltage of 5
volts is not enough.If the supply voltage is 12 volts, then the figure 1 can not
be applied, because if the control voltage is 0 and 5 volts then the LED will be
remain switched on.
Figure 2. Super
bright common anode driver circuit.
This problem can be solved by using the circuit as shown in Figure 2 namely by
adding a NPN transistor. This NPN transistor used as a voltage adjustment,
because by adding a NPN transistor, then when the controlling signal is high
input, then the base of PNP transistor will receive a low voltage (VCE tr 1 is
close to 0 volt) so that the 7 segment LED will be switched on, when the control
voltage is low level then the base of tr 2 will receive high voltage (12 volts),
then the LED will be switched off.
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