Summary of equivalent circuits of common electronic components[Copy link]
The equivalent circuit of electronic components is very useful for circuit analysis. It can help us understand the working principle of the component in the circuit and provide a deep understanding of the relevant characteristics of the component.
Chip capacitor equivalent circuitThe figure below shows the equivalent circuit of a chip capacitor.
From the equivalent circuit, we can see that the capacitor has parasitic inductance L and parasitic resistance R in addition to capacitance. Although the L and R values are very small, the inductance will take effect when the operating frequency is very high, and the inductance L and the capacitance C form an LC series resonant circuit.
Equivalent circuit of a capacitor with leads
The figure below shows the equivalent circuit of a capacitor with leads.
Compared with chip capacitors, its equivalent circuit has an additional pin distributed inductance, and it also has the characteristics of high-frequency series resonance.Equivalent circuit of polarized electrolytic capacitor
The figure below shows the equivalent circuit of a polar electrolytic capacitor without considering the pin distribution parameters.
In the equivalent circuit, C1 is a capacitor, R1 is a leakage resistor between two electrodes, and VD1 is an oxide film with unidirectional conduction characteristics.Equivalent circuit of large-capacity electrolytic capacitorAn electrolytic capacitor is a low-frequency capacitor, that is, it mainly works in circuits with lower frequencies and is not suitable for working in circuits with higher frequencies because the high-frequency characteristics of electrolytic capacitors are not good, and the high-frequency characteristics of electrolytic capacitors with large capacity are even worse.
The figure below shows the equivalent circuit of a large-capacity electrolytic capacitor. From the figure, we can find the reason why large-capacity electrolytic capacitors have poor high-frequency characteristics.
From the equivalent circuit, it can be seen that when an equivalent inductor L0 is connected in series, the larger the capacity of the electrolytic capacitor, the larger the equivalent inductor L0 and the worse the high-frequency characteristics.
Ordinary thyristor equivalent circuit
The figure below shows the schematic diagram of the structure and equivalent circuit of a common thyristor.
From the equivalent circuit, it can be seen that the ordinary thyristor is equivalent to a circuit in which two transistors are connected in a certain way.
Bidirectional thyristor equivalent circuit
The figure below shows the schematic diagram of the bidirectional thyristor structure and the equivalent circuit.
Equivalent circuit of a reverse conducting thyristor
The figure below shows the equivalent circuit of a reverse conducting thyristor.
It can be seen from the equivalent circuit that the reverse conducting thyristor is equivalent to connecting a diode in reverse parallel to an ordinary thyristor.
BTG thyristor equivalent circuit
The figure below shows the BTG thyristor structure diagram and equivalent circuit.
The figure below shows the equivalent circuit of a resistor. In the equivalent circuit, R is the nominal resistor, L is the distributed inductance, and C is the distributed capacitance. Since the distributed inductance L and the distributed capacitance C are both very small, their effects can be ignored when the operating frequency of the resistor is not very high.
In circuits with very high operating frequencies, high-frequency resistors should be used, whose distributed inductance L and distributed capacitance C are smaller than those of ordinary resistors.Varistor equivalent circuit
The figure below shows the equivalent circuit of a varistor. In the equivalent circuit, Rn is the grain boundary resistance, C is the grain boundary capacitance, and Rb is the grain resistance.
The figure below is a schematic diagram of the three working zones in the varistor's volt-ampere characteristic curve. Its three working zones include the pre-breakdown zone, breakdown zone and rising zone.
Inductor Equivalent CircuitThe inherent capacitance of an inductor is also called distributed capacitance and parasitic capacitance. It is caused by various factors and is equivalent to a total equivalent capacitance connected in parallel at both ends of the inductor coil.
The figure below shows the equivalent circuit of an inductor, where capacitance C is the inherent capacitance of the inductor, R is the DC resistance of the coil, and L is the inductance.
The inductor L and the equivalent capacitor C form an LC parallel resonant circuit, which will affect the stability of the effective inductance of the inductor.When an inductor works in a high-frequency circuit, due to the high frequency and small capacitive reactance, the equivalent capacitance has a great influence on the circuit operation. For this reason, the inherent capacitance of the inductor coil should be reduced as much as possible.When the inductor works in a low-frequency circuit, since the capacity of the equivalent capacitor is very small, its capacitive reactance is very large when the operating frequency is low, so it is equivalent to an open circuit, so it has little effect on the circuit operation.Different applications have different requirements for different parameters of inductors. Only by understanding the specific meanings of these parameters can we use them correctly.Varactor diode equivalent circuit
The figure below shows the equivalent circuit of a varactor diode.
C in the equivalent circuit is the variable junction capacitance, which can be approximately regarded as the total capacitance of the varactor diode, which includes the junction capacitance, case capacitance and other distributed capacitance. R is the series resistance, which includes the PN junction resistance, lead resistance and wiring resistance; L is the lead inductance.
Bidirectional trigger diode equivalent circuit
The figure below shows the structural diagram and equivalent circuit of a bidirectional trigger diode.
The figure below shows the equivalent circuit of a quartz crystal oscillator. From the equivalent circuit, it can be seen that the quartz crystal oscillator is equivalent to an LC series resonant circuit.
The figure shows the equivalent circuit of the ceramic filter. The ceramic filter is composed of one or more piezoelectric vibrators. The double-terminal ceramic filter is equivalent to an LC series resonant circuit. From the characteristics of the LC series resonant circuit, it can be seen that the impedance of the circuit is the smallest when resonating and it is purely resistive. The resonant frequency of the double-terminal ceramic filter used in different occasions is different.
The three-terminal ceramic filter is equivalent to a double-tuned intermediate frequency transformer, so its filtering performance is better than that of the two-terminal ceramic filter.
Circuit inside a common composite tube (Darlington tube)
There are 4 types of compound tube circuits. A compound tube is made by connecting two triodes in a certain way, which is equivalent to one triode. The following figure shows 4 types of compound tube equivalent circuits.
The trick to identify the polarity of compound tubes: the polarity of two transistors after being combined depends on the polarity of the first transistor.
High power composite tube internal circuit
The following figure shows the internal circuits of two types of high-power composite tubes. From the internal circuit, it can be seen that it is equipped with an overvoltage protection circuit (using a voltage-stabilizing diode).
A damping diode is required in the row output stage circuit. This damping diode is set inside some row output transistors and will be indicated in the circuit symbol of the row output tube.A small resistor R0 of 25 ohms is connected between the base and the emitter of this triode. Placing the damping diode inside the line output tube reduces the lead resistance, which is beneficial to improving the line scanning linearity and reducing line frequency interference. The resistor connected between the base and the emitter is to adapt the line output tube to work in a high reverse withstand voltage state.
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