Resistance and Impedance

Resistance is an important physical quantity in the circuit, which represents the resistance of the conductor to the current. The size of the resistance determines how easily the current flows in the conductor.

The unit of resistance is the ohm (Ω), which reflects the degree to which the conductor blocks the current. The greater the resistance, the stronger the conductor's blocking effect on the current, and the more difficult it is for the current to pass; the smaller the resistance, the weaker the conductor's blocking effect on the current, and the easier it is for the current to pass.

In the circuit, the role of the resistor is mainly reflected in two aspects: the 1 is to limit the size of the current to protect the circuit and equipment from overcurrent damage; the 2 is to convert electrical energy into heat energy through the heating effect of the resistor to achieve some specific functions, Such as heating, lighting, etc.

Definition of Impedance

Impedance is a complex representation of the ratio of voltage to current in an AC circuit, usually denoted by the capital letter Z. In an AC circuit, both current and voltage change with time, so the relationship between them cannot be simply described by the resistance in a DC circuit. The impedance contains not only the real part of the resistance, but also the imaginary part of the inductive reactance generated by the inductance and the capacitive reactance generated by the capacitance.

The complex form of impedance can be expressed:

Z = R jX

Where R is a resistance, X is an inductive or capacitive reactance (depending on whether the element in the circuit is an inductor or a capacitor), and j is an imaginary unit.

Calculation method of impedance

The calculation of the impedance depends on the type of components in the circuit. For a purely resistive circuit, the impedance is equal to the resistance value. For circuits containing inductors or capacitors, the calculation of impedance needs to consider the effect of inductive or capacitive reactance.

Pure resistance circuit: Z = R

Pure inductance circuit: Z = jωL, where ω is the angular frequency and L is the inductance value.

Pure capacitance circuit: Z = -j/(ωC), where C is the capacitance value.

For complex circuits containing multiple elements, the calculation rules of series and parallel impedances can be used to solve for the total impedance.

Application of Impedance in Circuit Design and Analysis

Circuit matching: In the process of signal transmission and reception, impedance matching is very important. If the source impedance and load impedance do not match, signal reflection and power loss can result. By adjusting the values of the circuit elements, impedance matching can be achieved, thereby improving signal transmission efficiency.

Filter Design: Impedance plays a key role in filter design. By selecting appropriate component values and connections, filters with specific frequency responses can be designed, such as low-pass filters, high-pass filters, band-pass filters, and band-stop filters.

Circuit stability analysis: Impedance analysis helps to evaluate the stability of the circuit. By calculating the input impedance and output impedance of the circuit, it is possible to judge whether the circuit has an oscillation tendency and take corresponding measures to eliminate the unstable factors.