How does bjt amplify

However, heat also depends upon it configuration. It is used in different things, such as an amplifier, oscillator, rectifier, switch, etc. A signal is just a general term used to refer to any particular current, voltage, or power in a circuit. A mplification is a ratio between two values which does not imply that the output value is greater than the input value.

Transistors are normally used as amplifiers. Some transistor circuits are current amplifiers, with a small load resistance, other circuits are designed for voltage amplification and have a high load resistance and others amplify power.

Considering the above diagram:. The small current travels from the voltage source into the base of the transistor. A current at the base turns on the transistor. The current is then amplified and travels from the emitter of the transistor to the collector. The amplified current is large enough to turn on and light the LED. Saturation — The transistor acts like a short circuit. Current freely flows from collector to emitter. Active — The current from collector to emitter is proportional to the current flowing into the base.

Reverse-Active — Like active mode, the current is proportional to the base current, but it flows in reverse. Current flows from emitter to collector not, exactly, the purpose transistors were designed for. Nearly all the examples we deal with here in Arduino-land reside in the digital realm where the transistors "active amplification mode" is mostly irrelevant because we are using it in "saturation" mode.

This is why we see so few good "analog amplification" examples in our little Arduino world. We are using them as switches where they behave in essentially a full-on or full-off switch mode to do things like drive a relay. You also seldom see just a "single" transistor analog amplifier because with just one transistor you don't get a lot of "result" if you are aiming for some serious punch.

The issue is that you have to fight with the parameters to keep the transistor operating in the Active region by employing careful use of signal biasing often just a set of resistors and signal coupling usually done with capacitors in a bipolar signal scenario High power BJT's usually have low gain and high base current requirements. This is often a killer to a small signal needing to be amplified so, as a result, multiple, carefully designed amplification stages of transistors are used to ultimately achieve the desired signal.

Driving a speaker, for example. By utilizing the transistors ability to take a small signal at the base pin and create a proportionally larger "result" from it, you get the amplification result that was not obvious to you.

This is something you DON'T get from a transistor when it is used as a switch. With amplification, you have to keep it OUT of saturation mode. Well because if you want amplification according to your definition then it is impossible to amplify anything at all. Not even laser action? Travelling wave tube? Seems pretty close to the definition as in both cases the signal is being added to as it goes through MarkT: Not even laser action? Seems pretty close to the definition as in both cases the signal is being added to as it goes through….

What the laser does is add more photons of the same energy to the stream. So, philosophically does a transistor amplify a current the same way? Lasers do that with photons, transistors can do that with electrons.

I use transistors as kind of a relay. This is because this mode gives the amplifier a high input impedance and a low output impedance. The voltage gain in this mode is slightly less than unity x 1 , but high current gain called h fc in common collector mode is available. Voltage Gain: Slightly less than unity 1. Because the base of the transistor is connected to ground in this mode, it forms an effective grounded earthed screen between output and input. Hons All rights reserved.

Revision Semiconductors 2. The transistor itself does not amplify anything by itself. But it allows you essentially to switch a higher power path by driving a low power one. You may have heard of the concepts, but you can't "know pnp and npn" and still ask a question like this Add a comment. Active Oldest Votes. Bimpelrekkie Bimpelrekkie Curd Curd Sign up or log in Sign up using Google. Sign up using Facebook.

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