Accidentally touching the + to the base of a NPN transistor could definitely fry it and the LED. I realize this method has it's downsides and it could expose the component to a small chance of possible ESD damages. This only allows a very small base-emitter current and the transistor will never saturate. I guess the explanation is that the skin resistance is very high. I used this method successfully without burning any transistor so far. To bias a PNP transistor in this mode you would have to touch the base and the ground in the same time like this: Chances are that your body potential is significantly different then the source voltage of the power supply and you only need about 0.6V to open the Base-Emitter junction through the resistance of your skin. Your body usually behaves like an antenna and will pick up some alternating millivolts from the environment. It helps if your fingers are not very dry. Then open the junction of the transistor by touching with your finger between collector and base like this. Just use an alligator clip or something similar like I’m using in this example. This setup is very quick and you don’t need to solder anything. And the - in the cathode of the LED like in the picture below. Connect the anode of the LED into the emitter.So suppose you don’t have a multimeter around, simply garb a 5 to 12V voltage source. It can even be a 9V battery or something similar. The first method I’m using the most, is the LED method.
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June 2023
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