Voltage stabilization circuit

We use power sources every day to charge our phones, run our TVs or computers, but we very rarely think about how they work. The main purpose of power supplies is to obtain a stable voltage, i.e. if we have 200-240 volts of alternating current voltage at the input, then at the output we should get a clear 5 volts of direct current. First, let's remember about methods of voltage transformation and one of the types of inductors - a voltage transformer. But even earlier we need to remember the concepts of current.
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Схема линейного блока питания.jpg

Direct and alternating current

We have already used an oscilloscope to explain the principles of operation of radio components, but it really gives an understanding of what current is and how it can be viewed. On an oscilloscope we see a graph of voltage versus time, so for example, imagine that we record temperature readings on a street thermometer every day, one cell of our graph is a day, now imagine that we have been keeping records for several decades and change the scale of our graph by moving it to graph paperor by averaging its value to the average value for the week, as a result, on a meter-long section of wallpaper we will get a sinusoid of increasing and decreasing temperature, now if you change the scale you can either make it smoother or see each bend in more detail. Now imagine that we moved from central Russia, where the temperature drops to -30 and rises to + 30 degrees, to New Zealand, where the temperature practically does not change depending on the time of day; on our graph by year there will be a straight line at +24 degrees.

Voltage transformer

From lat. transformare - “to transform, transform”
The transformer consists of a primary winding (usually a large number of turns, for example let’s take 10,000) and a secondary winding (for example, let’s also take 1000 turns, which is 10 times less). At its core, these are two inductor coils, around which a magnetic field arises if current flows through the coil. If we apply 220 volts to our coil, then it will have a resistance consisting of active (resistance of the copper wire) and inductive (resistance of the coil due to its physical properties to change current).

Since alternating current flows in the coil (primary winding), its resistance due to self-induction and active resistance is high. A magnetic field arises in the primary winding; a magnetically permeable medium (transformer iron, those plates that connect the primary and secondary windings) is used to propagate it. Immediately with the formation of a magnetic flux around the secondary winding, an EMF or voltage appears on it, the size of which depends on the transformation ratio, in our example it is 10,000/1000 or 1 to 10, or from 220 volts we get 22 volts, with the same frequency, but with one small assumption

Galvanic isolation, i.e. independence of the current in the first winding from the current in the second. Since electricians do not know what current (how large) you need, it is limited only by the cross-section of the wire and the power of the substation. i.e. if you short two wires in a socket, there will be a “drum” (you’ve probably tried it)). But if you close the contacts of the secondary winding of the transformer, then nothing will happen, since the current of the transformer is limited by its size.
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Diode bridge

If we take four diodes and connect them to a transformer, then we get that the lower half-wave of the sinusoid or everything that is below zero is turned upside down and, in fact, we no longer have an alternating current, but a pulsating one, since it does not change its direction, but only at some points it decreases.

Current rectification using a diode bridge is called full-wave.

For three-phase voltage, a diode bridge circuit of six diodes is used and is called a Larionov circuit, while a circuit with four diodes is called a Hertz circuit.

Anti-aliasing filter

This is a device for smoothing out ripple after rectifying alternating current. Those. the same depressions that form after the diode bridge become more compressed, since the capacitor accumulates some of the energy (voltage) on its plates and when a drop occurs, it releases it, it turns out that the higher the capacitance of the capacitor, the better the behavior of the power supply and the output voltage will be more stable. On the one hand, this is true, but on the other hand, a large capacitor capacity leads to an increase in cost and size, and for modern power supplies this is not so important, since then we will stabilize the voltage using linear regulators.

Measuring voltage with a multimeter

If we look at an oscilloscope, we see how the voltage changes from +22 volts to -22 volts, we rectify this voltage and see not 22 volts after the diode bridge, but say 18 volts (for example), this is obtained from the addition of all voltage values at certain points in time. those. if we take a drawing and record readings every millimeter of the graph, then at some moments our voltage will drop to zero, but most of the time it will be above half.

If we connect a capacitor, then the multimeter shows 20 volts, which is also due to the average voltage reading. In general, the voltages can be as follows

Instantaneous tension
Peak voltage
Medium voltage
RMS voltage (Indicated by multimeter)
Average direct voltage

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