![]() ![]() The input signal of an amplifier is a voltage or a current, and the output is an amplified version of the input signal. The transistor is used as an amplifier to raise the strength of a weak input signal. Work as a Switch Transistor Work as an Amplifier This time transistor does not allow to flow of the current from the Collector to Emitter, so No the current also flows from the source (+5v) to the ground through the load (LED). In this condition is said to be the transistor is in its cut-off region. When the no voltage/current is applied to the base terminal, then the transistor will work in reverse biased condition and it turns on and acts as an open switch. This time transistor allows to flow of the current from the Collector to Emitter, so the current also flows from the source (+5v) to the ground through the load (LED). In this condition is said to be the transistor is in its Saturation region. When the sufficient positive voltage/current is applied to the base terminal, then it will work in forward biased condition and it turns on and acts as a closed switch. The input voltage is applied to the base terminal to control the transistor biasing. The emitter terminal is connected to the ground of the power supply, the collector terminal is connected to the positive power supply through a load, here we have used a LED as load. Here we are using a simple circuit to easily understand how it works as a switch. The BD139 transistor can be used as a switch to control lamps, relays, or even motors. The BD139 transistors have numerous use in the applications of switches and amplifiers i.e., the two main uses of any transistor existing in the electronics arena. ![]() ![]() When no current is applied at the base terminal of this transistor, it turns off and this situation is termed as cut-off region. The maximum voltage that can be provided across emitter and collector terminals is 80 V. And the magnitude of this supplied current must be more in than the collector current. If the maximum current of 1.5A is supplied throughout this transistor then it will be in Saturation Region. In this condition, the maximum current drawn by the emitter and collector is 1.5A. When the sufficient current is applied to the base terminal, then it will work in forward biased condition and it turns on. Since BD139 is an NPN transistor so the majority of charge carriers are electrons. The collector and emitter are left open when the base pin is held at the ground and are closed when a signal is provided to the base pin. As mentioned BD139 is an NPN transistor, so, in it the p-doped layer is embedded between two n-dopped layers. ![]()
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