loks Red LED +10v D₁ + Vin ми Red o + Vout LED Dz 오- -10V
Light-emitting diodes (LEDs) are diodes made with III-V compound semiconductor materials such as aluminum gallium arsenide (AlGaAs), aluminum indium gallium phosphide (AlInGaP) or indium gallium nitride (InGaN), instead of silicon. The LEDs emit light when the device is operated under forward bias. LEDs of different colors have different turn-on voltages VD(on). For example:
VD(on) :
Red: ~ 1.6 V
Yellow: ~ 1.7 V
Green: ~ 1.8 V
Blue: ~ 2.8 V
White: ~ 3.8 V
(a) Model these five LEDs with a simplified piecewise linear model
(b) A rule of thumb is that it takes about 1 mA of current to “light” an LED while ~ 10 mA is needed for it to appear bright. Use the piecewise linear model for the LEDs, for the over-voltage indicator circuit to the right, find the values of Vin which will cause D1 or D2 to light (i.e. when ID1 or ID2 exceeds 1 mA).
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