What is a constant current transistor, its structure, characteristics, and application techniques

A constant current transistor is a special type of transistor that can achieve a constant collector current output by controlling the base current. In electronic circuits, constant current transistors are widely used in fields such as power supply, current source, and current control.

1、 Structure of Constant Current Transistor

The structure of the constant current transistor LM393N is similar to that of a regular transistor, consisting of an emitter, base, and collector. However, the constant current transistor has some special designs in its structure, such as adding a stabilizing diode, which enables it to achieve a constant collector current output.

 

Among them, R1 is the current limiting resistor, R2 is the base resistor, RG is the current stabilizing diode, and C is the bypass capacitor. A steady current diode is the core component of a constant current transistor, whose main function is to maintain a constant current at a constant voltage.

2、 Characteristics of Constant Current Transistor

1. Constant current output: Under normal operating conditions, the collector current of a constant current transistor is not significantly affected by input voltage and output load, thus exhibiting a constant current output characteristic.

2. High precision: Constant current transistors have high-precision current output, typically achieving an accuracy of around 0.1%.

3. Good stability: Constant current transistors have good temperature stability and power supply stability, and can operate within a wide temperature range and power supply fluctuation range.

4. Low noise: Due to the stable current output of the constant current transistor, its noise level is relatively low.

5. Low output voltage: The output voltage of a constant current transistor is usually low, ranging from a few hundred mV to several V.

3、 Application skills of constant current transistor

1. Constant current source: Due to its high precision and good stability, constant current transistors are commonly used in the design of constant current sources. For example, in power supply design, constant current transistors can be used to provide a constant current output to ensure circuit stability.

2. Current control: Constant current transistors can also be used for current control, for example, in LED driving circuits, constant current transistors are used to control the current of LEDs to ensure stable brightness.

3. Protection circuit: Constant current transistors can also be used in protection circuits, such as adding constant current transistors to power supplies to limit output current and protect loads and power supplies.

4. Choosing the appropriate resistance value: When using a constant current transistor, it is necessary to select the appropriate current limiting resistor and base resistor according to the specific application situation to ensure the stability and reliability of the circuit.

5. Pay attention to power supply fluctuations: The stability of constant current transistors is greatly affected by power supply fluctuations, so it is necessary to pay attention to the stability of the power supply, such as using voltage regulators and other power supply regulators to improve the stability of the power supply.

In short, constant current transistors have the characteristics of high precision and good stability, and are widely used in fields such as power supply, current source, and current control. In practical applications, it is necessary to select appropriate constant current transistors and circuit design schemes according to specific situations to ensure the stability and reliability of the circuit