LED dimmer uses only two lines


Posted on Jan 10, 2013

The circuit in Figure 1 provides 32 steps of brightness controlfrom 0 to 100%for a backlight or instrument panel, using just two general-purpose-microprocessor signals. In addition, the circuit requires little board space, because it uses only three SOT-23s and one µMax package. Although Figure 1 shows the circuit driving white LEDs, the load could also be a dc motor or an incandescent lamp. The basis of the circuit is a modified Schmitt-trigger relaxation oscillator (Figure 2). The output of IC1 is high when where k is the wiper position, VCC is the supply voltage, VD is the diode voltage, and VN and VP are the threshold voltages of the Schmitt trigger.






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