What is the effect of the internal resistance of the power supply on the voltage source current source?

When learning the current source and voltage source, the problem of the internal resistance of the power supply often confuses many people. Just remember that when the voltage source is connected to the external load, the internal resistance is considered to be in series with the external load; when the current source is connected to the external load, the internal resistance is considered to be Parallel to the external load, the smaller the internal resistance of the voltage source is, the better the current resistance is. The larger the internal resistance of the current source, the better! Do not understand why? What is the effect of the internal resistance on the power supply? Why do the internal resistance and the external load match the power output to reach the maximum power?

First, the basic concept

1. The circuit consists of a power supply and a load;

2. The circuit is divided into two parts: the inner circuit and the outer circuit, and the power circuit is the inner circuit;

3. When the current passes through the internal circuit of the power supply, there is also a resistor. This resistor is called an internal resistor.

4, the current also consumes electrical energy heating on the internal resistance;

5, as a power supply, the consumption of internal resistance is not only a kind of waste, but also the temperature rise of the power supply itself, and the power supply will be damaged in severe cases!

6, the internal resistance of the power supply is actually the conductor resistance!

Second, the internal resistance and the external load match the power output to reach the maximum power, why?

1, the power supply has two functions:

First, as the energy source of the load, we are talking about the power source;

The second is the information source of the load, which we call the "signal source"; as the power source, we hope that the internal resistance of the power supply is as small as possible, that is, the internal resistance is small and the output is high, that is, the efficiency is high; for example, the power supply system, Generators, transformers, etc. as power sources have small internal resistance. As a signal source, we require that the output signal power be as high as possible, for example, we want the sound of the speaker to be "high";

2. When is the output power of the signal source the largest, and the speaker is the loudest?

(1) When the resistance of the signal source is constant, when the resistance of the load is greater than the internal resistance and is getting larger and larger, although the energy consumed by the internal resistance is less than the load, the total signal power decreases, and the signal power obtained by the load decreases. From a mathematical point of view, it is a "reduction function";

(2) When the resistance of the signal source is constant, when the resistance of the load is less than the internal resistance, and getting smaller and smaller, although the total signal power rises, the energy consumed by the internal resistance is greater than the load, and the signal power obtained by the load is decreased. From a mathematical point of view, it is an "increasing function";

(3) In the case where the internal resistance of the signal source is constant, only when the resistance of the load is equal to the internal resistance, the energy consumed by the internal resistance is equal to the energy of the load, and the signal power obtained by the load is the largest, which is 50% of the total signal power. The point of view is the "maximum value";

Third, the voltage source requires the internal resistance to be as small as possible, the current source requires the internal resistance to be as good as possible!

1. When solving complex circuit analysis, we must equilibrate the actual power supply circuit into an ideal power supply; the main parameters of the actual power supply are internal resistance and electromotive force; and idealized power supply has two kinds:

(1) One is a voltage source, which has a constant terminal voltage in the circuit, which is also called a constant voltage source;

(2) One is a current source, which has a constant current in the circuit, also called a constant current source; it is not equivalent to directly convert the actual power supply in the circuit into an ideal power supply; the actual power supply equivalent can be changed into A voltage source is connected in series with an internal resistance, or equivalent to a current source in parallel with a resistor; after an equivalent change, the relationship between the components of the circuit becomes a single string-parallel relationship, thereby turning the complex circuit into a simple circuit;

2. How to understand "ideal constant voltage source, constant current source"? We all know the actual power supply:

(1) has internal resistance;

(2) There is a constant electromotive force;

(3) The voltage at the terminal end and the current at the end of the circuit vary with the load;

3. Under what circumstances can the actual power supply be equivalent to an "ideal constant voltage source, constant current source"?

(1) When the load resistance of the circuit is much larger than the internal resistance, or the internal resistance is small, it can be ignored, and can be regarded as a voltage source with a constant terminal voltage;

(2) When the load resistance of the circuit is much smaller than the internal resistance, or when the internal resistance is large to infinity, it can be regarded as a current source with a constant terminal current; for example, in the triode amplification circuit, the collector current Regardless of the load size, it can be regarded as a current source;

4, "The voltage source requires the internal resistance to be as small as possible, the current source requires the internal resistance to be as good as possible" is not appropriate, it should be said:

(1) The smaller the internal resistance is, the closer the actual power source is to the constant voltage source;

(2) The closer the internal resistance is, the closer the actual power source is to the constant current source;

(3) Or constant voltage source can be understood as the actual power supply with the smaller internal resistance;

(4) Or constant current source can be understood as the actual power supply with the better internal resistance;