When designing electrical circuits, situations are possible when a current of a certain magnitude flows in the circuit, and the load is designed for significantly lower consumption. Especially for this case, original circuit solutions were invented, called current dividers. Their work is based on the Kirchhoff's law known from the physics course.
Definition and principle of operation
The current divider is a special electrical circuit of their 2 resistors, through which it is possible to divide the total current I into two components (photo below).
Each of the components I1 and I2 takes on values depending on the ratio of the two resistors (they are inversely proportional to it). With equal resistors, half the current will flow through each of them.
note: The theoretical basis for the principle of operation of a resistive divider is the basic Kirchhoff's law (the sum of the currents at the output and input are equal).
Sometimes, for a figurative representation, the electron flow is compared with a fast river, in which the speed of water movement corresponds to the current strength in the conductor. If we divide its channel into two equal and parallel flowing parts, then the water pressure in each of them (current strength) will decrease exactly by half.
Analysis of the current sharing circuit
To begin with, let's present it in the form below.
The potential difference (voltage) between the input point "A" and the output "B" are the same for both resistors. Each of them has its own resistance, and their sum is calculated according to the formula for parallel connection, given below:
According to Kirchhoff's rule (first), the total current is defined as the sum of two components branching along chains. And the currents in each of these circuits are determined by the formulas, which include the values of the resistors installed in them. In other words, this can be expressed as follows: in order to change the current in the fan, for example, switched on instead of one of the resistances, it is enough to change the value of the second (parallel to it) resistor.
By installing a potentiometer with a variable value in its place, it is possible to regulate the rotational speed of the fan blades (change the current in it) within certain limits. These limits depend on the intrinsic resistance of the motor winding of the device and the range of change in the value of the potentiometer.
Current divider calculation example
As an example, consider the case of finding the values of I1 and I2 in an artificially organized current divider with a known total value of I = 0.6 Amperes. This will require the formulas shown in the photo below:
For example, R1 is 100 ohms and R2 is 20 ohms.
Further actions are as follows:
- According to the formula for the current in one of the branches, we find: I1 = 0.6x20 / (100 + 20) = 0.1 Ampere.
- For the other component, we determine: I2 = 0.6x100 / (100 + 20) = 0.5 Ampere.
- Since there is a drop in power on R1 and R2, they are also selected according to this indicator according to the formula: P = IхIхR.
For the resistor R1 P = 0.1x0.1x100 = 1 W, and for R2 this indicator is P = 0.5x0.5x20 = 5 W. Taking into account the margin, it selects the values of 2 and 10 watts, respectively.