Several methods of identifying equivalent circuit of circuit drawing

Method 1 ： Feature recognition

The characteristics of series parallel circuit are ：
The current in a series circuit does not diverge , The potential at each point decreases gradually ;
Current bifurcations in parallel circuits , Both ends of each branch are equipotential , Equal voltage between the two ends .
Identifying the circuit according to the characteristics of the series parallel circuit is one of the most basic methods to simplify the circuit .

Draw a picture 1 The equivalent circuit shown .

analysis ： Let the current be controlled by A End inflow , stay a Point bifurcation ,b Point confluence , from B End outflow . Access Rd a—R1—b and a—R2—R3(R4)—b The potential at each point decreases gradually , Of two branches a、b The voltage between the two points is equal , I know R3 and R4 After parallel connection, it is connected with R2 Series connection , And again R1 parallel connection , The equivalent circuit is shown in the figure 2 Shown .

Method 2 ： Current direction method

Current is the core of analyzing circuit . Start from the positive pole of the power supply ( A passive circuit may assume that current flows from one end to the other ) Follow the direction of the current , Go around the external circuit through each resistance to the negative pole of the power supply , All resistors through which current flows in sequence without bifurcation are in series , All the resistances through which the current flows separately with bifurcation are connected in parallel .

analysis ： The current flows from the positive pole of the power supply A Points are divided into three routes (AB The wire can be shrunk to a point ), Walk through the external circuit for a week , from D The point flows into the negative pole of the power supply . The first route R1 Through D spot , The second route R2 arrive C spot , The third way R3 Also arrived C spot , obviously R2 and R3 Connected at AC The two points are connected in parallel . Two 、 Three circuit currents are converged at c Meridians R4 arrive D spot , You know R2、R3 After parallel connection, it is connected with R4 Series connection , And again R1 parallel connection , Pictured 7 Shown .

Method 3 ： Equipotential method

In more complex circuits, we can often find the point where the electric potential is equal , Reduce all points with equal potential to one point , Or draw on a line segment . When there is a non power element between two equipotential points , It can be removed from consideration ; When a branch has neither power nor current , This branch can be cancelled . This method of the simple ratio circuit is called equipotential method .

example . Pictured 8 Shown , It is known that R1 = R2 = R3 = R4 = 2Ω , seek A、B Total resistance between two points .

analysis ： Imagine A、B The two points are respectively connected to the positive and negative poles of the power supply for analysis ,A、D The two points have equal potentials ,B、C The potentials at the two points are also equal , Draw two line segments respectively . resistance R1 Connect to A、C At two o 'clock , That is to say, it is connected to A、B At two o 'clock ;R2 Connect to C、D At two o 'clock , That is to say, it is connected to B、A At two o 'clock ;R3 Connect to D、B At two o 'clock , That is to say, it is connected to A、B At two o 'clock ,R4 Also connected to A、B At two o 'clock , It can be seen that all four resistors are connected to A、B Both points are connected in parallel ( chart 9). therefore ,RAB=3Ω.

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