Analyze the faults in the resistor parallel circuit

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Analyze the faults in the resistor parallel circuit [Copy link]

The resistor parallel circuit is the most basic parallel circuit. All responsible circuits can be converted into resistor series and resistor parallel circuits to understand the working principle. The characteristics of parallel circuits and series circuits are completely different. They are completely different circuits and cannot be equivalent to each other (resistor parallel circuit diagram).

The figure shows a resistor parallel circuit. It can be seen from the figure that the two pins R1 and R2 of the resistor are connected separately to form a parallel circuit of two resistors. +V is the DC working voltage of this circuit.

When R1 and R2 are connected in parallel in the circuit working in an AC circuit, the circuit form remains unchanged, but the DC voltage +V is changed into an AC signal.

When analyzing a resistor parallel circuit, it is important to understand the following resistor parallel characteristics.

1. The total resistance of a parallel circuit decreases as the number of parallel connections increases.

This is exactly the opposite of the total resistance value of a series circuit. If two 20KΩ resistors are connected in parallel, the total resistance after parallel connection is half of one of the resistors, which is 10kΩ. As shown in the figure below. The total resistance after parallel connection is R＜R1＜R2.

Note: In a resistor parallel circuit, the reciprocal of the total resistance value R after all resistors are connected together is equal to the sum of the reciprocals of the individual resistors in parallel. The formula is: 1/R=1/R1+1/R2+1/R3......

2. The total current of a parallel circuit is equal to the sum of the currents in each branch (diagram of the currents in each branch of a parallel circuit)

As shown in the figure, the current flowing through resistor R1 is I1, the current flowing through resistor R2 is I2, the total current of the parallel circuit is I, the current flowing out of the power supply +V is divided into two paths, one flowing through R1, and the other flowing through resistor R2. The sum of the currents in each branch is equal to the total current in the loop. For this specific circuit, it is I=I1+I2. If there are more parallel branches, then I=I1+I2+I3......

In a branch of a parallel circuit, the current in the branch is inversely proportional to the resistance of the resistor in the branch. A resistor with a large resistance has a small current in the circuit. On the contrary, a resistor with a small resistance has a large current in the circuit. From the formula I=U/R, we can see that when the current of resistor R1 is less than the current flowing through R2, as shown in the figure below:

Memory diagram of current characteristics of parallel circuit:

Using a river as an image, the water flowing out of the reservoir is divided into three paths and all flows into the sea, which is equivalent to the current flowing out of the power supply flowing into each resistance circuit branch.

3. The voltage across the parallel resistor is equal

In a parallel circuit, the voltage across each parallel resistor is equal (as shown below). Because the two resistors R1 and R2 are connected in parallel, the voltage across them is equal.

If more resistors are connected in parallel in the circuit, then the voltage across each parallel resistor is equal.

4. The main contradiction in the parallel circuit is the small resistance

In a parallel circuit, if the resistance of a resistor is much greater than the resistance of other resistors, the resistor does not play a major role and can be considered as an open circuit. In this way, only the resistor with a small resistance is left in the circuit.

When analyzing a parallel circuit, we must focus on the resistor with a small resistance. It is the main contradiction in this circuit, even though the resistor with a small resistance plays a major role in the parallel circuit, which is exactly the opposite of the series circuit.

4. Open circuit and short circuit fault detection method of resistor parallel circuit:

1) The open circuit fault detection method is as follows:

When the circuit is powered off, use the resistance range of the multimeter to measure the total resistance of the parallel circuit. Under normal circumstances, the measured total resistance value should be <R1 <R2.

If the measured resistance value is greater than R1 and greater than R2, it means that R1 or R2 in the circuit is open. It needs to be analyzed which circuit is open, or the current of each resistance branch can be measured to make a judgment.

2) The short circuit fault detection method is as follows:

If the total resistance is zero, it means that there is a short circuit in the parallel circuit. If you need to know the detailed location and cause, you need to do further testing. This is of great significance for troubleshooting, as it determines the scope of the fault circuit and the direction of inspection.

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The OP has a deep understanding of this and has done a lot of research. I look forward to sharing further.

HQ90

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