How does the transistor work in this circuit

In summary, the given circuit has an attached speaker that emits sound when S1 is down. When S3 is also down, the sound is lower pitched, and when both S1 and S3 are up, a high pitched sound is heard. The transistor in the circuit is configured as a Hartley Oscillator and its purpose is to change the tuning capacitor values and thus the frequency of the sound. It may be more effective if the transistor were NPN instead of PNP with the given bias voltages.
  • #1
gsingh2011
115
1
In the circuit attached, when S1 is down, a sound is emitted from the speaker. When S3 is down(connected) a lower pitched sound is heard. When S3 is up and S1 is up, a high pitched sound is heard. I don't understand why the pitch changes in those settings, and I also don't understand the purpose of the transistor in the circuit. Why does it need to be there?EDIT: To view the image you have to click on the thumbnail and then click on the image that comes up, which looks black, and then you'll see it. IDK why that's happening..
 

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  • #3
Also, I think the transistor should be NPN instead of PNP with the bias voltages in the given circuit.
 

1. How does a transistor amplify current in a circuit?

A transistor is a three-terminal semiconductor device that controls the flow of current between two of its terminals (called the collector and emitter) by varying the current at its third terminal (called the base). This variation in current at the base causes a larger current to flow through the collector and emitter, resulting in amplification of current in the circuit.

2. What is the role of the base in a transistor?

The base of a transistor acts as a control terminal. By applying a small current or voltage to the base, the transistor can switch between allowing or blocking the flow of a larger current through the collector and emitter. This makes the base an important component in controlling the amplification of current in a circuit.

3. How does a transistor act as a switch?

A transistor can act as a switch by controlling the flow of current between two terminals. When a small current or voltage is applied to the base, the transistor allows a larger current to flow through the collector and emitter, acting as an "on" switch. When no current or voltage is applied to the base, the transistor blocks the flow of current and acts as an "off" switch.

4. What is the difference between a bipolar junction transistor (BJT) and a field-effect transistor (FET)?

The main difference between a BJT and a FET is the way they control the flow of current. A BJT uses a small current at the base to control a larger current at the collector and emitter, while a FET uses an electric field to control the flow of current between its terminals. Additionally, FETs have a higher input impedance and faster switching speeds compared to BJTs.

5. How does the size of a transistor affect its performance in a circuit?

The size of a transistor can affect its performance in a circuit in several ways. For example, a smaller transistor will have lower power and current handling capabilities, but may have faster switching speeds. On the other hand, a larger transistor can handle more power and current, but may have slower switching speeds. Additionally, the size of a transistor can also affect its thermal properties and overall cost.

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