How to choose and use resistors?

Today's society is inseparable from electronic components. When working as a power engineer, it is inevitable to deal with various components. Electronic R&D personnel must consider many parameters of components to ensure the performance of the produced electronic products. It is good and less prone to problems; and for most electronics enthusiasts engaged in repair, production and simple design, practical problems can be solved as long as some important parameters of the components are considered.

The resistor selection process is as follows:

① Determine the resistance value. The resistance value of the resistor can be calculated using Ohm's law R=U/I=220V/0.01A=22000Ω=22kΩ.

② Determine the error. For the circuit, the smaller the error, the better. The resistor error chosen here is ±5%. If it is difficult to find a resistor with an error of ±5%, you can also choose a resistor with an error of ±10%. When selecting a resistor, the resistance, error, rated power and limit voltage of the resistor are mainly considered. The current I required through the resistor R is 0.01A. Please choose a suitable resistor to meet the actual requirements of the circuit.

When selecting a resistor, the resistance, error, rated power and limit voltage of the resistor are mainly considered.

③ Determine the power. According to the power calculation formula, the power of the resistor can be calculated as P=I2R=(0.01A)2×22000Ω=2.2W. In order to allow the resistor to be used for a long time, the power of the selected resistor should be more than twice the actual power. . The resistor power chosen here is 5W.

④ Determine whether the limit voltage of the selected resistor meets the circuit needs. When a resistor is used in a circuit with high voltage and low current, the power may meet the requirements, but if the limit voltage of the resistor is less than the voltage applied to both ends of the resistor, the resistor will be broken down.

The limiting voltage of the resistor can be found. The limit voltage of the resistor here is V≈331V. This value is greater than the 220V applied to both ends and can be used normally. When the resistor reaches the pole, in order to ensure that the resistor is not broken down in the circuit, a resistor with a larger resistance or a higher power can be selected according to the situation. To sum up, in order for the resistor R in the circuit shown in the figure to work properly and meet the requirements, a resistor with a resistance of 22kΩ, an error of ±5%, and a rated power of 5W should be selected.

Resistor selection tips:

In actual work, it is often encountered that the selected resistor cannot meet the requirements. In this case, the solution can be solved by the following method:

① For circuits with low requirements, when selecting a resistor, its resistance and power should be as close as possible to the required value, and the rated power can only be greater than the required value, otherwise the resistor will be easily burned out.

② If you cannot find a resistor with a certain resistance value, you can solve the problem by connecting multiple resistors in parallel or in series. The resistance of resistors increases when they are connected in series and decreases when they are connected in parallel.

③If the power of a certain resistor is not enough, you can use multiple low-power resistors with large resistance in parallel, or use multiple low-power resistors with small resistance in series. Whether in parallel or in series, each resistor can withstand the The power will become smaller. As for how much power each resistor should be selected, it can be calculated by P=U2/R or P=I2R, and then consider about twice the margin. The above is the selection and use of resistors, which requires everyone to constantly sum up experience in practice.