How to lower voltage: ways and devices

You need to know how to lower the voltage in the circuit so as not to damage electrical appliances. Everyone knows that two wires are approaching the houses - zero and phase. This is called a single-phase network. Three-phase is extremely rarely used in the private sector and apartment buildings. There is simply no need for it, since all household appliances are powered by a single-phase alternating current network. But in the technology itself it is required to make transformations - lower the AC voltage, convert it into a constant voltage, change the amplitude and other characteristics. It is these moments that need to be considered.

Voltage reduction with the help of transformers

The simplest way is to use an undervoltage transformer that performs transformations. The primary winding contains more turns than the secondary winding. If there is a need to reduce the voltage in half or three times, the secondary winding can and should not be used. The primary winding of the transformer is used as an inductive divider (if there are taps from it). In household appliances, transformers are used, with the secondary windings of which the voltage of 5, 12 or 24 Volts is removed.

These are the most commonly used values in modern household appliances. 20-30 years ago, most of the technology was powered by a voltage of 9 volts. A tube TV and amplifiers required a constant voltage of 150-250 V and an alternating current for filaments of 6.3 (some lamps were powered from 12.6 V). Therefore, the secondary winding of the transformers contained the same number of turns as the primary winding. In modern technology, inverter power supplies are increasingly being used (as in computer power supplies), their design includes a transformer of a boosting type, it has very small dimensions.

Voltage divider on inductances

Inductance is a coil wound with a copper (usually) wire on a metal or ferromagnetic core. A transformer is one of the types of inductance. If a pull is made from the middle of the primary winding, then there will be an equal voltage between it and the outermost terminals. And it will be equal to half the supply voltage. But this is the case if the transformer itself is designed to work with such a supply voltage.

But you can use several coils (for example, you can take two), connect them in series and switch them on to AC power. Knowing the values of the inductances, it is easy to calculate the drop on each of them:

1. U (L1) = U1 * (L1 / (L1 + L2)).
2. U (L2) = U1 * (L2 / (L1 + L2)).

In these formulas, L1 and L2 are the inductances of the first and second coils, U1 is the supply voltage in Volts, U (L1) and U (L2) is the voltage drop across the first and second inductances, respectively. The circuit of such a divider is widely used in circuits of measuring devices.

Dividers on capacitors

A very popular circuit, used to reduce the value of the AC mains. It can not be used in direct-current circuits, since the capacitor, according to Kirchhoff's theorem, in the DC circuit is a discontinuity. In other words, the current through it will not flow. But when working in an alternating current circuit, the capacitor has a reactive resistance, which is able to extinguish the voltage. The divider circuit is similar to the one described above, but capacitors are used instead of inductances. The calculation is made by the following formulas:

1. Reactance of the capacitor: X (C) = 1 / (2 * 3.14 * f * C).
2. Voltage drop on C1: U (C1) = (C2 * U) / (C1 + C2).
3. Voltage drop across C2: U (C1) = (C1 * U) / (C1 + C2).

Here C1 and C2 are the capacitance of the capacitors, U is the voltage in the supply network, and f is the frequency of the current.

Dividers on resistors

The circuit is similar in many respects to the previous ones, but constant resistors are used. The procedure for calculating such a divider differs slightly from those given above. The circuit can be used both in AC and DC circuits. We can say that it is universal. With it, you can assemble a step-down voltage converter. Calculation of the drop on each resistor is made by the following formulas:

1. U (R1) = (R1 * U) / (R1 + R2).
2. U (R2) = (R2 * U) / (R1 + R2).

It should be noted one nuance: the magnitude of the load resistance should be 1-2 orders of magnitude smaller than that of the dividing resistors. Otherwise, the accuracy of the calculation will be very rough.

Practical scheme of power supply: transformer

To select a power transformer, you need to know a few basic data:

1. Power consumers that need to connect.
2. The value of the mains voltage.
3. The value of the required voltage in the secondary winding.

To calculate the number of turns in the primary winding, you need 50 divided by the cross-sectional area of the core. The cross-section is calculated by the formula:

S = 1,2 * √P1.

A power P1 = P2 / EFFICIENCY. The efficiency of the transformer will never be more than 0.8 (or 80%). Therefore, the maximum value is taken as 0.8.

Secondary winding power:

P2 = U2 * I2.

These data are known by default, so it is not difficult to make a calculation. Here's how to lower the voltage to 12 volts using a transformer. But this is not all: household appliances are powered by direct current, and at the output of the secondary winding - variable. It will take several more transformations.

Power supply circuit: rectifier and filter

Next is the transformation of the alternating current into a constant one. For this, semiconductor diodes or assemblies are used. The simplest type of rectifier consists of a single diode. It is called half-wave. But the maximal distribution was received by the bridge circuit which allows not only to straighten an alternating current, but also to get rid as much as possible from pulsations. But such a converter circuit is still incomplete, since it is not possible to get rid of the variable component by some semiconductor diodes. And 220V lowering transformers are able to convert an alternating voltage into the same in frequency, but with a lower value.

Electrolytic capacitors are used in power supplies as filters. By virtue of Kirchhoff's theorem, such a capacitor in an AC circuit is a conductor, and when working with a constant-discontinuity. Therefore, the constant component will flow unhindered, and the variable will close itself, therefore, will not pass beyond this filter. Simplicity and reliability are exactly what characterizes such filters. Also, resistors and inductors can be used to smooth out ripple. Similar designs are used even in automotive generators.

Stabilization of voltage

You learned how to lower the voltage to the desired level. Now it needs to be stabilized. For this purpose, special devices are used - zener diodes, which are made of semiconductor components. They are installed at the output of the DC power supply. The principle of operation is that a semiconductor is able to pass a certain voltage, the surplus is converted into heat and is sent through the radiator to the atmosphere. In other words, if the output of the power supply is 15 volts, and the stabilizer is set to 12 V, then it will miss as much as necessary. A difference of 3 V will go to the heating element (the law of conservation of energy is valid).

Conclusion

A completely different design is the voltage regulator that reduces, it makes several transformations. First, the mains voltage is converted to a constant voltage with a high frequency (up to 50,000 Hz). It is stabilized and fed to a pulse transformer. Then the reverse transformation occurs to the operating voltage (network or less in value). Due to the use of electronic switches (thyristors), the DC voltage is converted into an AC voltage with the required frequency (in the networks of our country - 50 Hz).