Series resonant circuits are an important circuit structure widely used in electronic engineering. Their characteristic lies in that when the input signal frequency reaches a certain specific value, the circuit presents pure resistive properties, and at this time, the current in the circuit reaches a relatively large value. However, in practical applications, engineers often encounter the phenomenon of reduced resonant frequency, which may be caused by multiple factors and requires analysis from multiple perspectives such as the characteristics of circuit components and the external environment.
Firstly, the variation of inductance component parameters is one of the common reasons for the reduction of resonant frequency. The inductance of an inductor is not constant and is affected by various factors. When the operating temperature of the inductor rises, due to the increase in the resistivity of the conductor and the change in the permeability of the magnetic core material, the inductance often increases. Additionally, if the inductor operates for a long time under a large current, the magnetic core material may experience magnetic saturation, which also leads to an increase in inductance. According to the resonant frequency formula f = 1/(2π√LC), an increase in inductance L will directly result in a decrease in resonant frequency f. Therefore, in high-temperature or high-current working environments, the actual resonant frequency of the resonant circuit may be lower than the designed value.
Secondly, the performance changes of capacitive components are also important factors affecting the resonant frequency. During long-term use, especially for electrolytic capacitors, their capacitance gradually decreases over time. This phenomenon is more pronounced in high-temperature environments, as high temperatures accelerate the evaporation of the electrolyte and the deterioration of the dielectric material. Additionally, the equivalent series resistance (ESR) of capacitors increases with usage time. All these changes can affect the actual resonant characteristics of the circuit. It is worth noting that certain types of capacitors also exhibit voltage dependence, meaning their capacitance varies with the applied voltage, which can also lead to a shift in the resonant frequency.
Parasitic parameters in circuits should not be overlooked either. In practical circuits, both wires and component pins have non-negligible parasitic inductance and parasitic capacitance. Although these parasitic parameters have relatively small values, they can significantly affect circuit performance in high-frequency applications. Especially when the circuit layout is unreasonable, there may be considerable distributed capacitance between adjacent wires. These additional capacitances will be in parallel with the designed capacitance, resulting in an increase in the total capacitance. According to the resonant frequency formula, an increase in capacitance will lead to a decrease in resonant frequency. Therefore, in the design of high-precision resonant circuits, the influence of these parasitic parameters must be fully considered, and appropriate shielding and wiring measures should be taken.
The variation of ambient temperature also has a significant impact on the resonant frequency. An increase in temperature will cause the inductance of inductive components to increase, and at the same time, it will also change the capacitance of capacitive components. For different types of capacitors, the temperature coefficient may be positive or negative. For example, the temperature coefficient of ceramic capacitors is usually negative, while that of some film capacitors may be positive. This parameter change caused by temperature will directly affect the resonant frequency. In applications with higher requirements, inductive and capacitive components with matching temperature coefficients need to be selected, or temperature compensation measures should be adopted to stabilize the resonant frequency.
Component aging is another factor that needs to be considered. During long-term use, the parameters of electronic components gradually change. The insulating material of the inductor coil may age, causing changes in the inter-turn capacitance; the dielectric material of the capacitor also deteriorates over time. These aging phenomena usually lead to a slow decrease in the resonant frequency. Therefore, in resonant circuits that require long-term stable operation, high-quality and long-life components should be selected, and regular calibration and maintenance should be carried out.
The changes in the internal resistance of the power supply and the load impedance will also affect the resonant frequency. When the internal resistance of the power supply increases or the load impedance changes, the parameters in the equivalent circuit will change, thereby affecting the resonant conditions. This influence is particularly significant in resonant circuits with higher power. To reduce this impact, buffer amplifiers or impedance transformation networks can be added to the circuit.
In practical applications, multiple factors may act simultaneously, jointly leading to a reduction in the resonant frequency. For instance, a high-temperature environment may cause an increase in inductance and changes in capacitance at the same time, while component aging may further exacerbate these changes. Therefore, when analyzing and addressing the issue of a decreased resonant frequency, it is necessary to comprehensively consider all possible factors and adopt a combined approach of experimental measurement and theoretical analysis to accurately identify the main causes and implement corresponding solutions.
To maintain the stable operation of the resonant circuit, the following measures can be taken: select components with stable temperature characteristics; optimize the circuit layout to reduce parasitic parameters; use automatic frequency tuning circuits in critical applications; regularly calibrate and maintain the circuit; provide good heat dissipation conditions for the circuit. Through these measures, the offset of the resonant frequency can be effectively reduced, ensuring the normal working performance of the circuit.
Post time: Dec-30-2025