As a component, resistance is also called a resistor. The resistance of a conductor is usually represented by the letter R. The unit of resistance is ohm (ohm), referred to as ohm, and the symbol is Ω (Greek letter, pronounced Omega). Resistor is an ordinary component, but it has an unusual doorway. The resistance value of a resistive component is generally related to temperature, material, length, and cross-sectional area, and the physical quantity that measures the influence of temperature on resistance is temperature coefficient. It is defined as the percentage change of the resistance value when the temperature rises by 1°C; therefore, serial rs232 to wifi converter we generally only need to pay attention to the value, accuracy, and rated power, and these three indicators are appropriate.
The resistors are connected in series in the circuit so that the current has only one path, and the resistors R1 and R2 can be connected end to end in sequence, and finally R1+R2 can get a total resistance value R.
However, resistors in series can play various roles in different circuits. The following points are the roles played by resistors in circuits:
1. Partial pressure effect
No matter how big the resistance is, it will act as a voltage divider when it is connected in series in the circuit. Because in a series circuit, the currents across each resistor are equal, the sum of the voltages across each resistor is equal to the total voltage of the circuit. It can be seen that the voltage on each resistor is less than the total voltage of the circuit, so the series resistors divide the voltage. The formula in the figure below is the principle of partial pressure:
2. Current limiting effect
Some electronic components in the circuit are relatively "fragile", and if the current is too high, it will directly cause the device to burn out; in this case, we usually use a resistor in series in the circuit to keep the component within the normal value range; as shown below For the diode in the LED light-emitting circuit, if you want it to work normally without damage, you need to connect a current-limiting resistor in series, and the resistance value of the selected resistor needs to be determined according to the current that the component can withstand. Therefore, the resistor can be a small resistor or a large resistor.
3. The role in the signal line
The main purpose of connecting a small resistor in series in the signal line is to protect the pin, but its function can be divided into two points: impedance matching and reducing the steepness of the signal edge. For example, the serial resistance on the SPI signal line in the figure below is to improve the matching, reduce reflection, avoid oscillation, and facilitate debugging.
4. The role of the integral circuit
In an electronic circuit, one end of the capacitor is connected to a resistor, and the other end is grounded to filter out high frequencies, which is equivalent to integral and used for filtering. wireless communication The most typical application is the high and low audio frequency control in the amplifying circuit; for power circuits, the series resistance acts as a damping effect. The resistor dissipates the energy of the overvoltage, thereby dampening the oscillation of the circuit.