Now the voltage drop at the diode equals approximately those at the transistor, which is half the total voltage. The switching status of the transistor is "open", the lamp is turned off.Ī device with a resistance similar to those of the turned off transistor is a reverse biased diode. The power dissipation of the filament lamp is 18μV * 0.599μA = 10pW, by what the glow filament doesn't start glowing. The current running through the emitter collector line and so through the circuit is 12V / 20000030Ω = 0.599μA. Those of a 12V 5W filament lamp is approximately 30Ω, hence the voltage drop is just 18μV. The ohmic resistance of many electric devices is clearly below 1kΩ. While assuming an emitter collector resistance of 20MΩ (it's usually higher) the resulting voltage drop at a 1kΩ load resistor is just 0.005% of the total voltage, so if the circuit is connected to a battery with a nominal voltage of 12V, the voltage drop at the load resistor is just 0.6mV.
The voltage drop at the load resistor is: U Load = U Total * R Load / (R Load + R Transistor).
The emitter collector line of the transistor and the load resistor are forming a voltage divider. The most simple circuit consists of a transistor and a load resistor.
The electric curcuit attached to the emitter collector line of a bipolar junction transistor is "open", if 0V are attached to it's base pin. The resistance is high (above 20MΩ) if 0V are attached to the base pin and it becomes low (clearly below 100Ω) if those voltage increases above +0.6V (NPN types) respectively decreases below -0.6V (PNP types).Ī transistor can conceptually open or close electric circuits by altering the emitter collector resistance from it's minimum value ("close") to it's maximum value ("open") or vice versa. Ideally the resistance in the state "open" is infinite, while it is zero in the state "closed".Īt the previous chapter we have learned that the resistance of a bipolar junction transistor can be altered by attaching a voltage to the base pin. An electromechanical device consists at least of two electrical contacts which can be either in the state open, meaning the contacts are separated from each other, or in the state closed, meaning the contacts are touching each other. A switch is an electrical or electromechanical component that can interrupt the current running through an electric circuit.
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