Detailed explanation of the working principles of thirty common resistor circuits

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Detailed explanation of the working principles of thirty common resistor circuits [Copy link]

 

1. Resistor series circuit

The figure below shows a resistor series circuit. There are no other components, so it is called a pure resistor circuit.

In the circuit, the pins of resistors R1 and R2 are connected end to end. This connection method is called series connection, thus forming a series circuit of two resistors. +V is the DC working voltage in the circuit.

1) The total resistance of a resistor series circuit increases as the number of resistors connected in series increases

In a resistor series circuit, the total resistance after series connection is equal to the sum of the resistance values of each resistor involved in the series connection, that is, the total resistance R=R1+R2+R3+......

2) The current in a resistor series circuit is equal everywhere

The current flowing through each series resistor in a series circuit is equal and equal to the total current in the series circuit.

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2. Resistor parallel circuit

The figure below shows a resistor parallel circuit. In the circuit, the two pins of resistors R1 and R2 are connected separately to form a parallel circuit of two resistors. +V is the DC working voltage of this circuit.

1. The more parallel resistors there are, the smaller the total resistance of the circuit

In a parallel resistor circuit, the total resistance in the circuit decreases as the resistors are connected in parallel, which is exactly the opposite of the total resistance of a series circuit. If two 20K ohm resistors are connected in parallel, the total resistance after parallel connection is half of the resistance of one of the resistors, that is, 10K ohms, as shown in the figure below. The total resistance R after parallel connection is less than the resistance value of each resistor. In a resistor parallel circuit, the reciprocal of the total resistance of each resistor in parallel is equal to the sum of the reciprocals of the resistors involved in the parallel connection. 2. The total current of a parallel circuit is equal to the sum of the currents in each branch. The current flowing out of the power supply +V is divided into two paths, one flowing through resistor R1 and the other flowing through resistor R2. According to the node current law, the sum of the currents in each branch is equal to the total current in the loop. 34)]3. The voltage equalization characteristic of parallel resistors

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III. Series-parallel circuit of resistors

The figure below shows a series-parallel circuit of resistors consisting of three resistors. The resistors R1 and R2 in the circuit are connected in parallel, and then connected in series with the resistor R3. This circuit is a series-parallel circuit of pure resistors.

1. Total resistance characteristics of resistor series-parallel circuits

Serial-parallel circuits have some common characteristics of series circuits and parallel circuits.

In a resistor series-parallel circuit, the total resistance of the circuit is equal to the parallel value of the parallel resistors and the sum of the other series resistance values, and the R1 and R2 in the circuit are connected in parallel and then in series with the resistor R3.

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IV. Resistor voltage divider circuit

The following figure is a typical resistor voltage divider circuit, which is composed of two resistors, R1 and R2.

The input voltage is applied to resistors R1 and R2, and the output voltage is the voltage on the lower resistor R2 in the series circuit. There are two key points in analyzing the voltage divider circuit: analyzing the input voltage loop and finding the input end and finding the voltage output end.

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5. Resistor voltage divider circuit with load circuit

The figure below is a resistor voltage divider circuit after connecting to the load resistor. RL is the load resistor, which can be a resistor or a circuit.

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VI. Typical DC voltage supply circuit of resistors

Using resistors to add voltage to a certain point in the circuit, the most commonly used in electronic circuits is to add DC voltage. The figure below shows a typical DC voltage supply circuit. R1 in the circuit adds DC working voltage to the base of transistor VT1, because the transistor needs DC voltage when working in the amplification state. This circuit is also called a fixed bias circuit in the transistor amplifier.

R1 in the circuit is connected between the DC voltage +V terminal and the base of transistor VT1, so that the DC voltage +V can be added to the base of VT1. Of course, the base voltage of VT1 is lower than the DC voltage +V, which is equal to +V minus the DC voltage drop on the resistor R1 (the voltage across R1). The voltage drop on R1 is related to the resistance value of R1 and the current flowing through R1.

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Seven, one of the DC voltage supply circuits of resistance

The figure below is a DC voltage supply circuit. The working principle of this resistor DC voltage supply circuit is: add the DC voltage +V to the collector of the transistor VT1 through R1.

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8. Resistor DC voltage supply circuit 2

The figure below shows another DC voltage supply circuit. The working principle of this resistor DC voltage supply circuit is: add the DC voltage +V to the emitter of VT1 through R1.

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9. Resistor AC signal voltage supply circuit

Resistors can also add AC signal voltage to a certain point in the circuit. The figure below shows a resistor AC signal voltage supply circuit.

As can be seen from the circuit, the AC signal (audio signal) output from the radio circuit is added to the left channel circuit and the right channel circuit through resistors R1 and R2 respectively, thus dividing an AC signal into two signals, which are added to the two circuits respectively. The figure below is a schematic diagram of signal transmission, so that the left channel circuit and the right channel circuit amplify the same signal.

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10. Resistor Shunt Circuit 1

The figure below shows a shunt circuit composed of resistors. R1 in the circuit is a shunt resistor. If there is no resistor R1, all the current in the circuit flows through resistor R2. After adding R1, part of the current passes through R1, so there is current flowing through R1 in the total current.

If there is a total current, there is only this total current path. Now add a resistor to form a path, so that part of the total current is provided by this resistor, thus reducing the current in the original circuit path.

When a component cannot work safely because the current passing through it is too large, this resistance shunt method can be used to reduce the current flowing through the component. Doing so will affect the performance of some circuits. The larger the current divided, the greater the impact on the original performance of the circuit.

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11. Resistor Shunt Circuit 2

The figure below shows another resistor shunt circuit. There are a large number of various resistor shunt circuits in the whole circuit. The resistor shunt circuit uses a resistor in parallel with another component to allow part of the current to pass through the resistor to reduce the current flowing through the other component and reduce the burden of this component. There are many types of resistor shunt circuits depending on the components involved in the parallel connection. Here we explain the shunt circuit of the collector and emitter current of the transistor VT1.

In the circuit, R1 is a shunt resistor, VT1 is a transistor, and the resistor R1 is connected in parallel between the collector and emitter of the transistor VT1, so that R1 and the internal resistance between the collector and emitter of VT1 form a parallel circuit. After the shunt resistor R1 is added to the circuit, part of the current flows through the resistor R1, so the current flowing through the transistor VT1 is reduced, while the total current at the output end is not reduced. The total current is the sum of the currents flowing through the transistor VT1 and the resistor R1. Obviously, after the shunt resistor R1 is connected, it can protect the transistor. Such a resistor R1 is called a shunt resistor. Because the shunt resistor has the function of protecting another component, it is also called a shunt protection resistor.

In the resistor shunt circuit, the resistance value characteristics of the resistor for DC and AC are the same, so the shunt working principle for DC and AC circuits is the same, and the shunt working principle for AC signals of different frequencies is also the same. If other components or circuits are used to form the shunt circuit, the characteristics of the shunt circuit may change.

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12. Resistor current limiting protection circuit

The figure below shows a typical resistor current limiting protection circuit. When the DC voltage +V is constant, after adding resistor R1 to the circuit, the current flowing through the light-emitting diode VD1 is reduced to prevent VD1 from being damaged due to excessive current flowing through VD1. The larger the resistance value of resistor R1, the smaller the current flowing through VD1.

Resistor R1 is connected in series with VD1. The current flowing through R1 is equal to the current flowing through VD1. R1 reduces the current in the circuit, so it can protect VD1.

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13. Transistor base current limiting resistor circuit

The figure below shows a transistor base current limiting resistor circuit. VT1 in the circuit is a transistor used for amplification. The transistor has a characteristic that when its static current (base current) changes within a certain range, its current amplification factor can be changed. In some amplifiers, in order to adjust the transistor static current, the base bias resistor is set to a variable resistor, that is, RP1 in the circuit.

If there is no resistor R1 in the circuit, when the resistance of RP1 is adjusted to the minimum, the DC working voltage +V is added to the base of the transistor VT1, and a large current will flow through the base of VT1 and burn the transistor. Because the transistor is easily damaged when overcurrent occurs, a circuit that limits the current is too large should be added.

The resistor R1 prevents the base voltage of transistor VT1 from being equal to +V when the variable resistor is adjusted to the minimum. Because when RP1 is adjusted to the minimum, there is also resistor R1 connected in series between the DC working voltage +V and the base of VT1. R1 limits the occurrence of a large base current of transistor VT1, thus playing a protective role.

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Fourteen, DC voltage resistor step-down circuit

The figure below shows a typical DC voltage resistor step-down circuit. It can be seen from the circuit that the DC working voltage +V is added to the collector of the transistor VT1 through R1 and R2, and the DC voltage after passing through R1 is used as the DC working voltage of the VT1 amplifier. As the DC current flows through R1, there will be a DC voltage drop across R1, so that the DC voltage at the left end of R1 is lower than +V, which plays a role in reducing the DC voltage.

When current flows through a resistor, a voltage drop will be generated, which makes the voltages at both ends of the resistor unequal, one end is high and the other end is low, so that the resistor can reduce the voltage at a certain point in the circuit. This resistor step-down circuit not only reduces the DC voltage, but also can further filter the DC working voltage +V by cooperating with the filter capacitor C1, making the AC component in the DC voltage smaller.

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15. Multi-section DC voltage resistor step-down circuit

The figure below shows a multi-section DC voltage resistor step-down circuit. In the circuit, the DC voltage +V is stepped down by R2 and then added to the R1 circuit for further step-down.

In the multi-section resistor step-down circuit, the DC voltage after each section of the resistor step-down is different, and the DC voltage after the step-down is lowered, and the AC component of the DC voltage after the step-down is smaller.

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Sixteen, resistance isolation circuit

The figure below shows a typical resistance isolation circuit. The resistor R1 in the circuit isolates points A and B in the circuit, making the voltages at the two points unequal.

Points A and B in the circuit are separated by resistor R1. However, there is still a path between points A and B in the circuit, except that there is resistor R1. This situation in the circuit is called isolation.

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Seventeen. Resistor Isolation Circuit in Bootstrap Circuit

The figure below shows a practical resistor isolation circuit, which is a bootstrap circuit in an OTL power amplifier (a circuit that can increase the half-cycle signal amplitude under large signals). In the circuit, R1 is an isolation resistor.

In the circuit, R1 is used to isolate the DC voltage at point B from the DC working voltage +V, so that the DC voltage at point B may exceed +V at a certain moment. If there is no isolation effect of resistor R1 (R1 is short-circuited), the maximum DC voltage at point B is +V, and it is impossible to exceed +V. At this time, there is no bootstrap effect. It can be seen that after setting the isolation resistor R1, the bootstrap effect is better when the signal is large.

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18. Signal source resistance isolation circuit

The figure below shows a signal source resistance isolation circuit. The signal source 1 amplifier in the circuit is connected to the input of the post-stage amplifier through R1, and the signal source 2 amplifier is connected to the input of the post-stage amplifier through R2. Obviously, the outputs of these two signal source amplifiers are combined into one through R1 and R2.

If there are no R1 and R2 in the circuit, the output resistance of the signal source 1 amplifier becomes part of the load of the signal source 2 amplifier. Similarly, the output resistance of the signal source 2 amplifier becomes part of the load of the signal source 1 amplifier. In this way, the two signal source amplifiers will affect each other, which is not conducive to the stable operation of the circuit. The purpose of adding isolation resistors to the circuit is to prevent the output terminals of the two signal source amplifiers from affecting each other. After adding isolation resistors R1 and R2, the output terminals of the two signal source amplifiers are isolated, so that the harmful effects are greatly reduced, and the isolation of the circuit is achieved. After adding isolation resistors R1 and R2 to the circuit, the signal current output by the two signal source amplifiers can flow to the input terminal of the post-amplifier better instead of flowing into the output terminal of the other amplifier.

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19. Resistor isolation circuit in noise suppression circuit

The figure below shows the isolation resistor circuit in the noise suppression circuit. In the circuit, an isolation resistor R1 and a coupling capacitor C1 are connected between the preamplifier and the postamplifier circuit, and BT1 is an electronic switch tube.

Before analyzing the working principle of this circuit, we must first understand the working principle of the electronic switch tube in the circuit: when the base voltage of VT1 is 0V, VT1 is in the cut-off state, and the internal resistance between the collector and emitter of VT1 is very large, which is equivalent to an open circuit between the C and E poles. At this time, there is no effect on the circuit; when the base of VT1 is added with a positive voltage +V, VT1 is in a saturated conduction state, and the internal resistance between the collector and emitter of VT1 is very small, which is equivalent to connecting between the C and E poles. At this time, the right end of the resistor R1 is grounded, as shown in the equivalent circuit below. The analysis method of this circuit is: assume that the electronic switch tube VT1 is in the saturated conduction and cut-off states, and analyze the circuit working state.

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Twenty. Using resistors to implement current-voltage change circuits

The figure below shows a typical circuit that uses resistors to convert current changes into voltage changes. This is also the collector load resistor circuit of the transistor.

When current flows through R1, a voltage drop is generated on R1, causing the lower end of R1 (VT1 collector, point A in the circuit) to change. When the resistance value of resistor R1 is constant, when the current flowing through R1 increases, the voltage drop on R1 increases, and the VT1 collector voltage decreases; when the current flowing through R1 decreases, the voltage drop on R1 decreases, and the VT1 collector voltage increases.

It can be seen that R1 converts the change in the collector current of VT1 into the change in the voltage at point A in the circuit.

Mastering the characteristics of resistance can better understand the working principle of this circuit. When current flows through a resistor, a voltage drop will be generated at both ends of the resistor. This is the basic characteristic of a resistor. There are two details to pay attention to when analyzing the above circuit.

1) Voltage on R1 + voltage at point A = +V, +V is constant. When the voltage on R1 changes, the voltage at point A must change.

2) Regardless of whether the current flowing through R1 is DC or AC, and regardless of what type of AC current flows through R1, R1 can convert the change in current into a corresponding change in voltage.