The easiest way to understand Thevenin s theorem?

Thevenin's theorem (equivalent generator theorem). He pointed out that any linear active two-terminal network can be represented by an equivalent active.

The constant voltage source us of the equivalent voltage source is equal to the open-circuit voltage UOC of the linear active two-terminal network when the branch is disconnected; The equivalent voltage source internal resistance R0 is equal to the equivalent resistance between the two ends of the passive two-terminal network when all independent power supplies in the linear active two-terminal network are zero (i.e., the constant voltage source is short-circuited and the constant current source is open).

All connections in the circuit can be replaced with a series combination of a voltage source and a resistor.

Equivalent to the generator theorem, all connections in a circuit can be replaced with a series combination of a voltage source and a resistor.

1、"Open-circuit voltage method"It refers to a basic load circuit with a power supply and a connecting conductor, such as an open circuit somewhere and the voltage between two points is called the open circuit voltage. When the circuit is open, it can also be understood that an infinite resistor is connected at the open circuit, and the infinite resistance is connected in series in the circuit, and the open circuit is generally expressed as the power supply voltage when the circuit is open.

2、"Short-circuit current method"It refers to the current when the electrical appliance is not connected, which is equivalent to the current when the positive and negative poles of the battery are directly connected with a wire. Namely"Open the way"It is equivalent to adding an infinite resistance to the circuit, and a short circuit is equivalent to not adding a resistance in the middle. The open-circuit voltage is the voltage when the resistance is removed, that is, the power supply electromotive force, that is, the supply voltage.

The current is infinitely large and the voltage is infinitely small when it is short-circuited.

Thevenin's theorem points out that the electromotive force e of the equivalent two-terminal network is equal to the voltage when the two-terminal network is open, and its series internal impedance is equal to the impedance of the network when the independent source and capacitor voltage and inductance current in the network are zero. Let the two-terminal network n contain an independent power supply and linear time-invariant two-terminal components (resistors, inductors, capacitors), and these elements can be coupled to each other, that is, there can be controlled source and mutual inductance coupling; The load impedance z(s) is connected to ɑ and b at both ends of the network n, but there is no coupling between the negative load and the internal components of the network n, u(s) = i(s) z(s) (Figure 1). When all independent power supplies in the network n are not working (e.g., replacing the independent voltage source with a short circuit and the independent current source with an open circuit), and the initial value of all capacitor voltages and inductor currents is zero, the two-terminal network can be recorded as n0.

In this way, the current i(s) in the load impedance z(s) can generally be calculated as follows Eq. 1 (Fig. 2), where e(s) is the open-circuit voltage of the network n at both ends of Fig. 1, i.e., z(s) is the voltage u(s) at infinity; zi(s) is the impedance presented by n0 of the two-terminal network; s is a complex variable introduced by the unilateral Laplace transform.

Thevenin's theorem, also known as the law of the equivalent voltage source, is an electrical theorem proposed by the French scientist Léon Charles Davenin in 1883. Because as early as 1853, Helmholtz also proposed this theorem, so it is also called the Helmholtz-Thevenant theorem. Its content is:

The two ends of a linear network containing an independent voltage source, an independent current source, and a resistor are electrically equivalent to a series resistor combination of an independent voltage source v and a relaxed two-terminal network in terms of their external form. In single-frequency AC systems, this theorem applies not only to resistors, but also to generalized impedances. Thevenin's theorem has important applications in the analysis of complex DC circuits with multiple power supplies and multiple circuits.

The content of Thevenin's theorem is that any linear active two-terminal network can be replaced by an active branch for an external circuit, and the electromotive force of the active branch is equal to the open-circuit voltage of the two-terminal network containing commas and the impedance is equal to the incoming impedance after the two-terminal network of the active source is transformed into a passive network.

In terms of port characteristics, it can be equivalent to a single-port network with an electric open voltage source and a resistor connected in series. The voltage of the voltage source is equal to the voltage UOC of the single-port network when the load is open, and the resistance R0 is the equivalent resistance of the single-port network N0 obtained when all independent power supplies in the single-port network are zero.

The content of Thevenin's theorem is that any linear active two-terminal network can be replaced by an active branch for the external circuit, and the electromotive force of the active branch is equal to the open-circuit voltage of the passive two-terminal network, and its impedance is equal to the incoming impedance after the active two-terminal network is transformed into a passive network.

Thevenin's theorem: A linear resistor single-port network n with an independent power supply can be used in terms of port characteristics to be a single-port network with a voltage source and resistor connected in series. The voltage of the voltage source is equal to the voltage UOC of the single-port network when the load is open, and the resistance R0 is the equivalent resistance of the single-port network N0 obtained when all the independent blocking power supplies in the single-port network are zero.

In 1883, it was proposed by the Frenchman Davenin. Because in 1853 the German Helmholtz also proposed, it is also called Helmholtz's Veenant theorem.

Any single-port network with independent sources, linear resistors, and linearly controlled sources (two-terminal networks) can be equivalent to a single-port network (two-terminal network) with a voltage source connected in series with resistors. The voltage of this voltage source is the open-circuit voltage of this single-port network (two-terminal network), and this series resistance is the equivalent resistance of all independent sources in the network when all independent sources in the network are set to zero.

A two-terminal network consisting of a voltage source, a current source, and a resistor can be equivalent to a series equivalent circuit of a voltage source UOC and a resistor RO. The UOC is equal to the open-circuit voltage when the two-terminal network is open; RO is called Thevenin equivalent resistance, and its value is the equivalent resistance when all voltage and current sources in the network are zero, as seen from the ports of the two-terminal network. The branch of the voltage source UOC and the resistor RO is called the Thevenin equivalent circuit.

To apply Thevenin's theorem, it is important to pay attention to:

Thevenin's theorem is only equivalent to external circuits, not to internal circuits. In other words, it is not possible to apply the theorem to find the equivalent power supply electromotive force and internal resistance and then go back to find the current and power of the original circuit (i.e., the internal circuit of the active two-terminal network).

When applying Thevenin's theorem for analysis and calculation, if the active two-terminal network after the branch is still a complex circuit, Thevennan's theorem can be applied again until it becomes a simple circuit.

Thevenin's theorem applies only to linear active slow-hinged two-terminal networks.

Thevenin's theorem, also known as the equivalent voltage source law, can be used to equate a complex active linear two-terminal circuit to a power supply model in which a voltage source and a resistor are connected in series.

1. Thevenin's theorem reads: any active linear two-terminal network n with an independent power supply, a linear resistor and a controlled source can be equivalent to a power supply model with a voltage source and a resistor in series in terms of its port characteristics. The voltage of the voltage source is equal to the voltage UOC of the active two-terminal network when the load is open; When the series resistance r0 is equal to the zero of all independent power supplies in the active spine two-terminal network (independent voltage source short circuit, independent current source open circuit), the port equivalent resistance of the passive two-terminal circuit n is obtained.

2. Steps to solve Thevenin's theorem.

1. First remove the load resistor r l for a given circuit.

2. Replace all sources with their internal resistors.

3. If the power supply is ideal, short-circuit the voltage source and open the current source.

4. Now find the equivalent resistance at the load terminal, which is the Thevenin resistance (r th).

5. Draw the Thevenin equivalent circuit by connecting the load resistor, and then determine the desired response. This theorem is probably the most widely used network theorem. It is suitable for situations where it is necessary to determine the current or voltage through any one element in the network.

Thevenin's theorem is a simple way to solve complex networks.

3. Learn Thevenant's Law.

First of all, we have to understand what an active two-terminal network is and it must be linear, which can be understood so simply, that is, a circuit with a power supply; Then there is the conversion of voltage and power supply electromotive force and internal resistance, that is, multiple power supplies with medium leakage are converted into one power supply electromotive force, and the unrelated resistance is converted into electromotive force internal resistance, and finally a simple linear circuit is obtained. Conversion Method: Voltage Section:

In addition to calculating the partial open circuit, that is, moving it out of the circuit, and then using Ohm's law to calculate the voltage at both ends of the open circuit to get the electromotive force we want from the power supply, it is enough to move out the resistance part: also remove the part to be calculated, and then look at all the voltages as short circuits, and then calculate the total resistance to get the internal resistance. And then you get the simple circuit.