How does transistor amplify signal

I don't see how a transistor is "amplifying" anything. The collector and emitter are hooked up to a completely separate power source.

For example, it's not taking the 0. How is this amplification? It's about as much "amplification" as my little Arduino is doing by sending a 5V signal to a relay that "amplifies" a V AC circuit connected on the other side, but I don't ever hear people say that a relay is amplifying voltage or current.

It seems to me that a transistor is merely controlling a greater voltage or current with its own smaller voltage and current. Am I missing something? I can't expect to take a single little 5V 1A power supply and through a transistor turn it into 12V or 5A, right? If the base current was 1mA and the gain was a collector current of mA 'could' flow. If your collector relay coil was ohms and the supply voltage was 5 volts, 5 -.

If your collector resistor was ohms and the supply voltage was 5 volts, 5 -. So using this definition of amplification, a relay is also amplifying current, just in a binary fashion compared to the Active operational mode of a transistor where the current from collector to emitter is proportional to the current flowing into the base.

A 40mA current on a relay pin coming from a 5V source gets amplified to a 5A VAC current when the relay switches on a microwave. A 5A current could flow if the relay had a 40mA current.

In the case of the transistor that will be the ratio of collector current divided by base current. Of course, the conservation of energy always applies. Yes, a relay is something like an amplifier. So is the gas pedal in your car When you drive your car, the strength of your foot isn't moving the car. Power steering amplifies the force of your arms.

Power brakes amplify the force of your foot. On the other hand, a transformer is like a lever. A step-up transformer converts to higher voltage at lower current and a step-down transformer reduces the voltage and increases the current.

Note that I'm talking about AC transformers, not DC power supplies which can sometimes be quite a bit less efficient. But they do, but not as often because amplifying a digital signal is normally called "fanout" or "buffering" or "boosting".

There's nothing mere about controlling, that's how nearly all amplifiers work lasers and masers are the exception. With the help of the following transistor amplifier circuit, one can get an idea about how the transistor circuit works as an amplifier circuit. In the below circuit, the input signal can be applied among the emitter-base junction and the output across the Rc load connected in the collector circuit. For accurate amplification, always remember that the input is connected in forward-biased whereas the output is connected in reverse-biased.

For this reason, in addition to the signal, we apply DC voltage VEE in the input circuit as shown in the above circuit. Generally, the input circuit includes low resistance as a result; a little change will occur in signal voltage at the input which leads to a significant change within the emitter current. Because of the transistor act, emitter current change will cause the same change within the collector circuit.

At present, the flow of collector current through an Rc generates a huge voltage across it. Therefore, the applied weak signal at the input circuit will come out in the amplified form at the collector circuit in the output.

In this method, the transistor performs as an amplifier. Transistors are valves for flowing charge instead of flowing haudraulic fluid. What is my understanding is that for a transistor to amplify you need to bias it properly.

Forward biasing of BE junction makes it a conducting diode so input resistance is less. Reverse biasing CE junction makes it non conducting diode so output resistance is high. And if Ic is almost equal to Ie then the current causes a low voltage drop at input and large one at output. This is why its called an Amplifier. With a transistor, you can achieve this: Give a small signal ac at input, and get a larger valued higher amplitude signal at output.

But this is not all. You have to give DC supply at collector and base; emitter if required. This is called biasing the dc point. The rms power you get at the output will be less than the dc power you have supplied. DC analysis: don't consider any ac signal. Find out the values of all diode currents based on dc voltage at various nodes Collector, base , emitter. This is done by using KVL along various loops. Going further, the diode has forward resistance.

So the actual model will be like this:. From DC analysis, you must have found the value of Ie. Vout will depend on Ic. Ic will depend on Ib. Ib will depend on Vin and Re. Re we have found from DC analysis. By looking at this, you can make out that the output signal will be an amplified one, right?

Note: This was just to give you an intuitive idea that amplification does take place. But whether you will get amplification or not depends on whether the transistor is in linear amplifier , saturation or cut off switch.

Again, what will be amplified current or voltage depends on type of configuration. So that all comprises of chapters of any standard book on analog theory. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.

Create a free Team What is Teams? Learn more. Basic questions about transistor amplification Ask Question. Asked 9 years, 10 months ago. Active 5 years, 9 months ago. Viewed 49k times. Alin Green Noob Green Noob 4 4 gold badges 10 10 silver badges 15 15 bronze badges. A lot of confusion, do transistors amplify current, do transistors amplify voltage etc. This in effect increases forward bias, which causes base current to increase at the same rate as that of the input sine wave.

Emitter and collector currents also increase but much more than the base current. With an increase in collector current, more voltage is developed across Rl. Since the voltage across Rl and the voltage across Q1 collector to emitter must add up to Vcc, an increase in voltage across Rl results in an equal decrease in voltage across Q1.

Therefore, the output voltage from the amplifier, taken at the collector of Q1 with respect to the emitter, is a negative alternation of voltage that is larger than the input, but has the same sine wave characteristics.

During the negative alternation of the input, the input signal opposes the forward bias. This action decreases base current, which results in a decrease in both emitter and collector currents. The decrease in current through Rl decreases its voltage drop and causes the voltage across the transistor to rise along with the output voltage.

Therefore, the output for the negative alternation of the input is a positive alternation of voltage that is larger than the input but has the same sine wave characteristics. By examining both input and output signals for one complete alternation of the input, we can see that the output of the amplifier is an exact reproduction of the input except for the reversal in polarity and the increased amplitude tens of millivolts as compared to a few volts.

The PNP version of this amplifier is shown above. With a negative Vcc, the PNP base voltage is slightly negative with respect to ground, which provides the necessary forward bias condition between the emitter and base.