Voltage dividers are widely used in electronics, because they are the ones that optimally solve the problems of voltage regulation. There are various schematic solutions: from the simplest, for example, in some wall lights, to quite complex ones, as in the control boards for switching the windings of the normalizers of the mains voltage.
What is a voltage divider? The wording is simple - it is a device that, depending on the transmission coefficient (set separately), adjusts the value of the output voltage relative to the input.
Previously, on store shelves it was often possible to meet a sconce lamp designed for two lamps. Its feature was that the lamps themselves were designed to operate with a voltage of 127 volts. At the same time, the entire system was connected to a household electrical network with 220 V and worked quite successfully. No miracles! The thing is that the method of connecting the conductors formed nothing more than a voltage divider. Recall the basics of electrical engineering, namely, parallel and serial connection of consumers. As you know, with a sequential switching method , the current strength is equal, and the voltage changes (remember Ohm's law). Therefore, in the example with a lamp, the same type of lamp is connected in series, which gives a decrease in the voltage supplying them by half (110 V). Also, the voltage divider can be found in a device that distributes the signal from one antenna to several TVs. In fact, there are many examples.
Let's look at the simplest voltage divider based on two resistors R1 and R2. Resistors are connected in series, the input voltage U is applied to the free terminals. There is an additional output from the midpoint of the conductor connecting the resistors. That is, three ends are obtained: two are the external conclusions (between them the full value of the voltage U), as well as the middle one, forming U1 and U2.
Perform the calculation of the voltage divider, using Ohm's law. Since I = U / R, U is the product of current and resistance. Accordingly, in the area with R1, the voltage will be U1, and for R2 it will be U2. The current is equal to (serial connection). Given the law for the complete circuit, we find that the supply U is the sum of U1 + U2.
What is the current equal to under these conditions? Generalizing the equations, we get:
I = U / (R1 + R2).
From here you can determine the voltage value (U exit) at the output of the divider (this can be either U1 or U2):
U exit = U * R2 / (R1 + R2).
For dividers on adjustable resistances, there are a number of important features that must be taken into account both at the calculation stage and during operation.
First of all, such solutions cannot be used to regulate the voltage of powerful consumers. For example, in this way it is impossible to power the electric motor. One reason is the ratings of the resistors themselves. Resistances per kilowatt, if they exist, are massive devices that dissipate an impressive portion of energy in the form of heat.
The resistance value of the connected load should not be less than the electrical resistance of the divider circuit itself, otherwise the whole system will need to be recounted. Ideally, the difference between the R divider and the R load should be as large as possible. It is important to accurately select the values of R1 and R2, since overestimated values will entail an excessive voltage drop, and underestimated ones will overheat, spending energy on heating.
When calculating the divider, they usually select the value of its current several times (for example, 10) more than the amperage of the connected load. Next, knowing the current and voltage, calculate the total resistance (R1 + R2). Then, according to the tables, the nearest standard values of R1 and R2 are selected (taking into account their allowable power in order to avoid excessive heating).