Elenco's PK-201 Experiment #19: The Darlington

In this experiment, the transistor configuration is called the Darlington configuration, current is amplified twice. All the current flowing through the emitter of the first transistor (left) will flow to the base of the second transistor (right). This means that the current flowing into the base of the left transistor will be amplified twice (once by each transistor), or twice the amount of base current is needed to control the larger current in the circuit turning on the LED. To turn on both transistors the capacitor voltage must exceed 1.4V before the LED will light. And, since the input current to the base is so small, it will take much longer to discharge the capacitor. In the video, I show the voltage at the capacitor. First, when the switch in on, charging. Second, when the switch is off, discharging. In addition, midway through the video, I show the voltage at the collector of the right transistor as voltage is pooling. Last, in the video I short the capacitor to discharge it much faster. The pictures below the video show the voltage at each transistors in the order of base, collector, and emitter. For some reason, at times, Blogger does not let me insert text for all my images.  

 

 

Left Transistor base voltage

Left Transistor collector voltage

Left transistor emitter voltage

Right transistor base voltage