LED Animation - Montage LED
Simple LED control (Light Emitting Diode):
The two diagrams below are used to control a light emitting diode (LED in French, English LED).Diagram with NPN bipolar transistor diagram with PNP bipolar transistor
Why use a transistor instead of directly controlling the LEDs: already for the current drawn by the LED. The controller can not always generate the necessary current. Then the voltage V may be different from the output voltage of the steering body. What is the difference between the two schemes: The two commands are reversed: a state low on the base of the NPN bipolar transistor will cause the LED will be off. The same low state on the basis of the PNP transistor will make the LED will be on. Conversely, a high on the base of the NPN light the LED, and the same state on the PNP to turn off. How to size the components of the first scheme: It is assumed that the bipolar transistor is on and operates in saturated mode: the voltage between the collector and the emitter is VSAT (given by the component manufacturer). The VDEL voltage is the voltage drop in the on state of the LED. it is also given by the component manufacturer Hence the following equation:VR2 = R2 x IDEL according to Ohm's law Example: we want to have a 2mA in a voltage drop of 2V LEDs. The bipolar transistor has used VSAT 0.2V. The supply voltage is 5 V volts. We deduce R2 = 1400 Ohm. Important note: all size we have seen vary with temperature and depending on the dispersion of the components. For information, R1 is to limit the current in the base of the NPN transistor. It should nevertheless ensure that the base current is sufficient to saturate the transistor. Power loss: In the transistor: P ~ = VSAT = 0.2 x I x = 2mA 0.4mW In the LED P = VDEL IDEL x = 4mW In Resistance: P = R x = 5.6mW IDEL² is thus seen that to dissipate 4mW useful in LED we spent 5.6 + 0.4 + 4 = 10mW.
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LED Simple operation
simple electronic assembly LED
LED Animation - Montage LED