Introduction and functions of series, parallel and mixed circuits of resistors

1. Series circuit of resistors

Connecting two or more resistors in sequence without branches in the middle is called series connection. As shown in the picture.

series connection of resistors

Resistor series circuits have the following characteristics:

(1) The current flowing through each resistor is equal, that is, the current intensity is equal everywhere.

Series resistance current relationship

(2) The total voltage across the circuit is equal to the sum of the voltages across each resistor.

Voltage relationship between series resistors

(3) The total resistance of a series circuit is equal to the algebraic sum of each series resistance.

Resistance relationship between series resistors

(4) The voltage distribution of the resistor series circuit is proportional to the resistance value.

(5) The power consumed by each resistor in the series circuit is proportional to its resistance value.

The function of series resistor:

(1) Current limiting. For example, in a circuit connected to an LED light, a resistor must be connected in series to limit the current, because the general operating current of LED lights is between a few milliamps and more than ten milliamps. If the resistor is not connected in series, the current flowing through the LED may be much greater than normal value, and burn out the LED.

(2) Partial pressure. It is still an LED lamp circuit. The voltage at which the LED lamp is working is about 1 to 3 volts. When designing the circuit normally, it is impossible to design a power supply specifically for the LED lamp. In the actual design, resistors are connected in series to divide the voltage, so that the LED The lights work normally.

2. Resistor parallel circuit

Two or more resistors are connected between the same two points in the circuit so that the voltage at both ends of each resistor is the same. This is called a parallel connection of resistors.

Resistors in parallel

(1) The voltage at both ends of the resistor is equal.

Voltage relationship between parallel resistors

(2) The total current in the circuit is equal to the sum of the currents in each resistor.

Current relationship between parallel resistors

(3) The reciprocal of the total resistance (equivalent resistance) of a parallel circuit is equal to the sum of the reciprocals of each parallel resistance.

Resistance relationship of parallel resistors

(4) The current distribution of the circuit is inversely proportional to the resistance value.

(5) The power distribution of a resistor parallel circuit is inversely proportional to the resistance value.

The role of parallel resistors:

(1) Diversion. For example, when we design a current source, we have a sampling resistor, which requires a resistor with a small resistance and high power. But when you don’t have a resistor with enough power on hand, you can choose multiple resistors with small resistance in parallel. Then the power required by each resistor will not be very high and the design requirements can be completed.

3. Resistor mixed circuit

A circuit with both series and parallel resistors is called a mixed circuit of resistors.

The general steps for drawing an equivalent circuit diagram are as follows:

(1) According to the circuit structure, mark letters on each connection point of the circuit.

(2) Ignore the wire resistance. If there is no resistance between the two connection points, the two points are equipotential points, which can be considered as the same point and marked with the same letter.

(3) Starting from the terminal to be sought, draw a circuit diagram with clear direction and structure according to the circuit structure or current division and closing.