Full-wave rectifier: principle of operation, calculation, circuits

Almost all electronic devices operate on direct current. This approach significantly reduces the number of electronic components used, the size of the circuit and the cost of manufacturing the device.

Rectifiers are used to convert alternating electrical voltage into direct voltage. The article will give a detailed explanation of what full wave rectifiers are. Describes their operating principle, varieties, main advantages and disadvantages.

Diode bridge.

A diode bridge is a small circuit made up of 4 diodes and designed to convert
alternating current to direct current. Unlike a half-wave rectifier, which consists of a single diode and allows current to pass only during the positive half-cycle, a bridge circuit allows current to pass during each half-cycle. Diode bridges are made in the form of small assemblies enclosed in a plastic case.

Four pins come out of the assembly body opposite which are marked “+

", "
-
" or "
~
", indicating where the bridge has
an entrance
and where
the exit is
. But not necessarily diode bridges can be found in the form of such an assembly; they are also assembled by connecting four diodes directly on the printed circuit board, which is very convenient.

For example. One of the diodes of the bridge has failed, if the assembly is still standing, then we safely throw it away, and if the bridge is assembled from four diodes directly on the board, we replace the faulty diode and everything is ready.

In circuit diagrams, a diode bridge is indicated by including four diodes in a bridge circuit, as shown in the left part of the lower figure: here, the diodes are like the arms of a rectifier bridge. This graphic designation of the bridge can be found in old magazines on radio engineering. However, today, basically, a diode bridge is designated in the form of a rhombus, inside of which there is a diode icon, indicating only the polarity of the output voltage.

Now let's look at the operation of a diode bridge using the example of a low-voltage rectifier. In such a rectifier, using four diodes, during each half-wave, two diodes of the opposite arms of the bridge, connected in series with each other, but counter to the second pair of diodes, operate alternately during each half-wave.

From the secondary winding of the transformer, alternating voltage is supplied to the input of the diode bridge. When on top

(according to the diagram) a positive half-cycle of voltage occurs at the output of the secondary winding, the current flows through diode
VD3
, load
Rн
, diode
VD2
and to
the lower
terminal of the secondary winding (see graph
a
).
Diodes VD1
and
VD4
are closed at this moment and no current flows through them.

During another half-cycle of alternating voltage, when the plus is on the lower

(according to the diagram) at the output of the secondary winding, the current flows through diode
VD4
, load
Rн
, diode
VD1
and to
the upper
terminal of the secondary winding (see graph
b
).
At this moment, diodes VD2
and
VD3
are closed and do not allow current to pass through themselves.

As a result, we see that the signs of the voltage on the secondary winding of the transformer change, and a current of one direction

(see graph
in
).
In such a rectifier, both half-cycles of alternating current are usefully used, therefore such rectifiers are called full-wave rectifiers
.

And in conclusion, we note that the operation of a full-wave rectifier compared to a single-wave rectifier is much more efficient:

The ripple frequency of the rectified current has doubled;
2.
The gaps between pulses have decreased, which makes it easier to smooth out ripples at the rectifier output;
3.
The average value of the direct current voltage is approximately equal to the alternating voltage acting in the secondary winding of the transformer.

And if such a rectifier is supplemented with a filtering electrolytic capacitor

, then you can safely power an amateur radio design with it.

Well, you and I have almost finished studying diodes. Of course, not everything is given in these articles, but only the basic concepts, but this knowledge will already be enough for you to assemble your own amateur radio design for your home, which uses semiconductor diodes.

And for additional information, watch a video that tells you how to check a diode bridge with a multimeter

Good luck!

1. Borisov V.G - Young radio amateur. 1985 2. Goryunov N.N., Nosov Yu.R. - Semiconductor diodes. Parameters, measurement methods. 1968 3. Pasynkov V.V., Chirkin L.K. - Semiconductor devices: Textbook. for universities for special purposes “Semiconductors and dielectrics” and “Semiconductor and microelectronic devices” - 4th ed. reworked and additional 1987

Marking [edit | edit code ]

diode material:

1 or G - germanium or its compounds
2 or K - silicon or its compounds
3 or A - gallium compounds
4 or I - indium compounds

C - bridge
number (2...4 digits) Designate the serial number of the development of this type of bridge.
letter

A diode bridge is an electrical circuit designed to convert alternating current into pulsed direct current. The invention of the circuit in 1897 is attributed to the German physicist Leo Graetz, although English-language sources claim that back in 1895 the diode bridge was created by the “Polish Edison” - electrical engineer Karol Pollak. The scheme became most widespread after the widespread introduction of semiconductor diodes.

Diode Characteristics

How to check a generator diode bridge with a multimeter
Let's look at the characteristics of the KD411AM diode. We look for its characteristics on the Internet, typing into the search “datasheet KD411AM”

To explain the parameters of the diode, we also need its current-voltage characteristic

1) Reverse maximum voltage Urev is the voltage of the diode that it can withstand when connected in the reverse direction, while current Irev will flow through it - the current strength when the diode is connected in reverse. When the reverse voltage in the diode is exceeded, a so-called avalanche breakdown occurs, as a result of which the current sharply increases, which can lead to complete thermal destruction of the diode. In our diode under study, this voltage is 700 Volts.

2) Maximum forward current Ipr is the maximum current that can flow through the diode in the forward direction. In our case it is 2 Amperes.

3) Maximum frequency Fd, which must not be exceeded. In our case, the maximum diode frequency will be 30 kHz. If the frequency is higher, our diode will not work correctly.

Application of diode bridges

How does a voltage rectifier work?

And the short one is the cathode.

Parallel connection of LEDs If a 5 volt connection is necessary to install a pair of diodes, then a limiting type resistor with a resistance of no more than Ohms is connected to the electrical circuit in a series manner. In this case, it is worth remembering that the voltage drop across the LED will be the opposite for a conventional diode - VD1. When connecting LEDs of the same type in parallel, it is enough to calculate the parameters of one resistor, and the rest will be of the same value.

Used to simplify the designation of the two previous schemes.

This is the most important thing to remember. Due to this unfortunate event, all possible current will flow through the two surviving LEDs, naturally exceeding the rated one.

For calculation, you should take the maximum value of 3.7V. The maximum quantity is used in Chinese corn light bulbs, from 30 to LED pieces.

At the same time, a hole also forms in its old place. It involves a combination of parallel and serial connections. Diagram for connecting LEDs to volts Limiting the current level under alternating voltage conditions is carried out by resistors, capacitors or inductors.

Physical properties of pn junction

Minus on the first leg, plus on the second. Voltage drop across LEDs of different colors. It would seem that the situation can be corrected by the circuit shown in Figure 5. The first circuit of the rectifier device was assembled using radio tubes and was considered a complex and expensive solution. Comments on the article: 26 Good and bad circuits for connecting LEDs In previous articles, various issues of connecting LEDs were described.

The pulsations that appear must be removed, otherwise the electronic circuit will not be able to work normally. But we must not forget that some part of the voltage must remain for the quenching resistor, at least 2 volts. Figure 12 shows the SSC connection circuit for powering LEDs connected in parallel. The diode has very low internal resistance; if you turn it on without ampere limitation, it will burn out. LEDs based on solid solutions of zinc selenide ZnSe had a higher quantum yield, but they overheated due to high resistance and were short-lived. Rectifier circuits

What diodes are needed for a diode bridge, how to choose the right diodes for rectification.

Sometimes, when you have to deal with power supplies (repairing them, assembling them yourself), you come across its rectifier part, which converts alternating voltage into direct voltage. This part is nothing more than a diode rectifier bridge. For electrical engineers, it is known what it is and what the function of this element of electrical circuits is. For the uninitiated, let me explain - most electrical equipment contains in their circuits a power supply that reduces the mains voltage of 220 volts to the lower voltage that is used by devices (3, 5, 9, 12, 24 volts, these are the most common values of reduced voltages). The network uses alternating current, and almost all electronic circuits operate on direct current. So, a diode bridge is used to convert alternating voltage to direct voltage.

Rectifier diode bridges can be ready-made assemblies in a single housing, or they can be home-made, which are soldered together from four identical diodes. What diodes are needed for a homemade diode bridge and how to choose the right ones for a rectifier? Everything is quite simple. The main parameters for choosing diodes for a bridge are voltage (reverse) and current (which they can pass through themselves without overheating).

Let me remind you that when diodes are directly connected (the plus of the diode to the plus of the applied voltage, and the minus of the diode to the minus of the applied voltage) to the power supply, electric current passes through them. In this mode (open), a small voltage of about 0.6 volts is deposited on them. Like any other conductors, they have their own internal resistance (which causes this small voltage drop across them in the open state). The larger it is, the less current the diode can pass through itself. If a constant reverse voltage is applied to the diode (the minus of the source is applied to the plus of the diode, and the plus of the source is applied to the minus of the diode), then the diode will operate in the blocking mode. It will not pass direct current through itself (it will be closed).

So, there is a maximum value of reverse voltage that a diode can withstand without entering the mode of electrical and thermal breakdown. It is this reverse voltage that needs to be taken into account when choosing diodes for the rectifier bridge. If a voltage of 220 volts AC is supplied to the diode bridge, then the bridge diodes must be designed for a higher voltage (with a margin of at least 25%). And it’s better to take it with a fairly large reserve. This will protect the semiconductors from accidental voltage surges coming from the network. Nowadays, ordinary, small power supplies are equipped with diodes of the 1n4007 series, whose reverse voltage is 1000 volts, and they can withstand long-term current up to 1 ampere (at a temperature of 75 degrees).

The second, and perhaps the main characteristic of a rectifier diode is the current strength that it can pass through itself for a long time (without overheating). Initially, you should know what maximum current your power supply is designed for. And only after this you need to select rectifier diodes for the bridge. For example, you decide to make yourself a homemade regulated power supply with an output voltage of up to 15 volts and a maximum current of 6 amperes. Therefore, for such a power source you need to take diodes designed for a current of about 10 amperes (plus a certain current reserve). A current of 6 amperes seems to be relatively considerable. It will heat the diodes of the rectifier bridge. This means that a cooling radiator must be provided for these diodes and the bridge.

Let me remind you that most semiconductor components are made of silicon, and this material has a maximum operating temperature of 150-170 ° C. Going beyond these limits destroys the semiconductor, in our case the diodes of the diode bridge. It is better to keep the temperature of the diodes within 75 °C. Place a small radiator on the bridge and see if the temperature at maximum load of the power supply does not go beyond the permissible limits.

There are quite a large number of diode bridges and diodes (for them). When choosing, first use a search engine to find a reference table of diodes and diode bridges, which shows the main technical characteristics of rectifiers. Select the most suitable component based on reverse voltage and current ratings. If you put diodes with high rated currents and voltages on the diode bridge, it’s okay, it will be even better, like an excess reserve. But it’s not worth choosing smaller ones or right next to each other.

Video on this topic:

PS In addition to the main characteristics (current and voltage) of the diodes that will be placed on the diode bridge, you also need to pay attention to the frequency at which they can operate normally. The network frequency of 50 hertz is quite low and almost all diodes are suitable for it. The above 1n4007 diode has an operating frequency of 1MHz. Paying attention to frequency is important for electrical circuits designed for really high frequencies.

Purpose and practical use

Options for manufacturing power supplies for an 18 V screwdriver

The scope of use of a bridge made of diodes is quite wide. These can be power supplies and control units. It is installed in all devices powered by a 220 volt industrial network. For example, TVs, receivers, chargers, dishwashers, LED lamps.

Cars cannot do without it either. After starting the engine, the generator starts working, producing alternating current. Since the on-board network is all powered by constant voltage, a rectifier bridge is installed through which rectified voltage is supplied. The same constant signal also recharges the battery.

The rectifier device is used to operate the welding machine. True, it uses powerful devices that can withstand currents of more than 200 amperes. The use of diode assembly in devices provides a number of advantages compared to a simple diode. This straightening allows you to:

increase the ripple frequency, which can then simply be smoothed out using an electrolytic capacitor;
when working together with a transformer, get rid of the bias current, which makes it possible to more efficiently use the overall power of the converter;
pass more power with less heat, thereby increasing efficiency.

But it is also worth noting the drawback due to which in some cases the bridge is not used. First of all, this is a double voltage drop, which is especially sensitive in low-voltage circuits. And also, when some of the diodes burn out, the device begins to operate in half-wave mode, which is why parasitic harmonics penetrate into the circuit, which can damage sensitive radioelements.

power unit

Not a single modern power supply can do without a rectifier. High-quality sources are manufactured using bridge rectifiers. The classic scheme consists of only three parts:

A step-down transformer.
Rectifier bridge.
Filter.

A sinusoidal signal with an amplitude of 220 volts is supplied to the primary winding of the transformer. Due to the phenomenon of electromagnetic induction, an electromotive force is induced in its secondary winding and current begins to flow. Depending on the type of transformer, the voltage value is reduced by a certain value due to the transformation ratio.

An alternating signal with reduced amplitude appears between the terminals of the secondary winding. In accordance with the diode bridge connection diagram, this voltage is supplied to its input. Passing through the diode assembly, the alternating signal is converted into a pulsating one.

This form is often considered unacceptable, for example, for sound equipment or lighting sources. Therefore, a capacitor connected in parallel with the output of the rectifier is used for smoothing.

Three-phase rectifier

In production and in places where a three-phase network is used, a three-phase rectifier is used. It consists of six diodes, one pair for each phase. Using this type of device allows you to obtain a higher current value with low ripple. This, in turn, reduces the requirements for the output filter.

The most popular options for connecting three-phase rectifiers are the Mitkevich and Larionov circuits. In this case, not only six diodes can be used simultaneously, but also 12 or even 24. Three-phase bridges are used in diesel locomotives, electric vehicles, on drilling rigs, and in industrial gas and water purification plants.

Operation of the rectifier for an active load.

Half-wave rectifier.

Let's place a rectifier diode in front of the load. That is, we have a half-wave rectifier.

Let's put together the same circuit. My transformer is toroidal, with a power of 60 W, with a voltage of the secondary winding about 20 volts (rated load current 3.8 A, rated voltage 16.5 Volts), current of the transformer XX is 7 mA. To measure its current, I placed a 1.0 Ohm resistor in the gap of the primary winding, and a 0.1 Ohm resistor in the gap of the secondary winding (series with the load). To measure alternating and pulsating current and voltage in circuits, I used a root-mean-square (RMS) microvoltmeter B3-57, and for measuring in DC circuits, a Mastech MY64 digital multimeter.

For measurement safety, this entire structure was connected via an isolation transformer. Variable wire resistances of various values with a power of 25 W were used as load resistors. The effective load current was set to 0.5 amperes (figure above). The measurement limit is 100 mV, the shunt in the secondary circuit is 0.1 Ohm. The resistance of the variable resistor was 19 Ohms, the effective voltage at the load was 9.5 volts. That is, the power consumed by the load turned out to be 4.75 W. Let's measure the current consumed by the primary winding.

The primary winding current turned out to be 97 mA, minus 7 mA XX, for a total of 90 mA. The voltage on the primary winding is 215 volts. The power consumed by the primary winding turned out to be 19.35 W, that is, 4 (four) times more than the power of the consumed load. Why is that? For those who are interested in all the details of the processes taking place in a transformer, I recommend reading the primary sources given at the end of the article; for those who are too lazy to read, I will try to explain it in a simple way.

When installing a diode in series with the load, we get a half-wave rectifier. The load is supplied with a voltage (current) pulse only during the positive half-cycle, and nothing during the negative half-cycle (pause). As a result, the average voltage on the load decreases by more than two times (more precisely by 2.2) compared to the voltage on the secondary winding. The average current through the diode corresponds to the load current, and the effective current of the diode and the secondary winding itself is 1.57 times greater than the load current. Let's calculate the power of the secondary winding; Load current is 0.5 A, multiply by 1.57 = 0.785 (secondary winding current). We multiply the resulting current by the voltage of the secondary winding (19 Volts) 0.785x19 = 14.9 W - this is the output power of the secondary winding, plus transient processes during operation of the diode (valve) are also added here, plus reactive currents that simply heat the winding, in As a result, the power of the transformer is at least 3.5 times greater than the power consumed by the load. Even when this circuit is operating, a constant component appears in the secondary winding (due to the fact that the current in the winding flows only in one direction during one half-cycle), which magnetizes the transformer core and the greater the load current, the greater the current. Because of this, the properties of the core deteriorate and the XX current increases, as a result of which the power consumption of the transformer increases (we got 4 times more power).

For example, already with a load current of 1.0 Ampere, the load voltage was 9.0 Volts, the load resistance was 9.0 Ohms, the load power was 9.0 W. The primary winding current turned out to be 230 mA (minus 7 mA) for a total of 223 and the voltage on the primary winding was 210 volts. The total power consumption of the transformer is 46.83 W, that is, 5.2 times more than the power consumed by the load. The idle current increased greatly with increasing load current (which increased the magnetization of the core).

Full-wave rectifier.

Well, we've sorted out the half-wave rectifier, let's move on. Let's see how the full-wave circuit behaves. What is a full-wave rectifier circuit? These are two half-wave rectifiers that operate on a common load. Each rectifier has its own winding, but unlike the other, it is antiphase, as a result of which both half-cycles are rectified (entered into the load), due to which the efficiency of such a rectifier, compared to a half-wave rectifier, increases twice.

Let's see how he behaves. Let's assemble a full-wave rectifier circuit. This circuit requires a transformer tapped from the midpoint of the secondary winding. The transformer is different, the secondary winding has a voltage of 193-193 Volts, its current is 36 mA (as I found it). Using wire resistors I set the load current to 150 mA.

The load resistor turned out to have a resistance of 1.17 kOhm, the measured voltage across it was 175 Volts. The power consumed by the load turned out to be 26.17 W. Let's look at the current of the primary winding.

The primary winding current is 210 mA, minus the XX current (36) for a total of 174 mA. The power consumed by the transformer was 38.28 W. This is 1.46 times more power consumed by the load. As you can see, the performance here is much better than that of a half-wave rectifier. Go ahead.

Bridge rectifier circuit.

Let's check how the bridge rectifier circuit behaves. To do this, we will assemble the following diagram.

Let’s take the transformer that was there before, with one secondary winding from the first case under consideration for a half-wave rectifier. I set the load current to 0.5 A, the variable wire resistance turned out to be 32 Ohms. Load voltage 16 Volts. The power consumed by the load turned out to be 8 W.

We look at the current consumed by the primary winding.

Primary current 53 mA minus XX current (7 mA) = 45 mA. The power consumed by the primary winding was 9.9 W. This is 1.23 times more than the power consumed by the load. As you can see, the performance here is even better than that of a full-wave rectifier, not to mention a half-wave rectifier.

Main characteristics

Let's consider the main characteristics of semiconductor diodes. Their designation in English-language technical documentation (the so-called Datasheet) is given in Latin letters:

Vrpm is the peak or maximum reverse voltage. If this voltage is exceeded, the pn junction is irreversibly destroyed.
Vr(rms) – average reverse voltage. Normal for operation, the same as Urev in the characteristics of domestic components.
Io – average rectified current, the same as Ipr for domestic ones.
Ifsm – peak rectified current.
Vfm - voltage drop in forward bias (in the open conducting state) is usually 0.6-0.7V, and higher for high-current models.

When repairing electronic equipment and power supplies or designing them, beginners ask: how to choose the right diode bridge?

In this case, the most important parameters for you will be reverse voltage and current. For example, to select a 220V diode bridge, you need to look at models with a rated voltage greater than 400V and the required current, for example, KBPC106 (or 108, 110). Its technical characteristics:

maximum rectified current – 3A;
peak current (short-term) – 50A;
reverse voltage – 600V (800V, 1000V for KBPC108 and 110, respectively).

Remember these characteristics and you can easily determine which option to choose from the catalog.

Features of rectifiers

The rectifier for the welding machine is made according to a bridge circuit. When manufacturing and using B200 diodes, it is necessary to take into account that their housing is energized.

Therefore, when the rectifier is installed on a radiator, it must be isolated from the rest of the circuit elements, from the device body and from neighboring diodes too. And this creates certain inconveniences for the welder.

You have to use a larger body. To reduce the dimensions of the device, a VL200 rectifier device is used, which has a different polarity. This allows semiconductors to be combined into two paired heatsinks.

In recent years, quite powerful diode bridges in one housing have begun to be produced. In size, such a design of diodes approximately corresponds to a matchbox, has a platform for landing a radiator, and a maximum forward current of 30-50 A. The diode assembly has a significantly lower cost compared to B200 diodes.

If the operation of the device requires a more powerful bridge, then this problem can be easily solved by using parallel connection of bridge assemblies. However, their reliability in this case will be lower than that of single powerful diodes.

Radio amateur

A simple and popular program among radio amateurs for calculating a bridge rectifier

Good afternoon, dear Radio Amateurs! Today on the “Amateur Radio” website, in the “Technology” section, we will look at another program for radio amateurs. Not so long ago, in the article “Power supplies for amateur radio devices,” we looked at the operation of rectifiers and smoothing filters for power supplies for amateur radio devices . Most often, radio amateurs in their practice build power supplies based on a full-wave rectifier in a bridge circuit using a capacitor as a smoothing filter. In order not to bother with manual calculations of such power supplies and to make your life easier, you can use a special amateur radio program - Rectifier 1.0.

The Rectifier 1.0 program and is intended for calculating a full-wave rectifier using a bridge circuit. The program not only calculates the characteristics necessary for designing a rectifier, but also offers options for rectifier diodes and smoothing capacitors.

The program is very easy to use. In the input data section you must enter: - the required voltage at the rectifier output; – the amount of current consumed by the load; – as well as the permissible value of rectified voltage ripple. The calculation results immediately appear: - data on the transformer (voltage on the secondary winding, minimum permissible current in the secondary winding and transformer power; - data for selecting diodes (reverse DC voltage, permissible forward average current, power dissipation and heat sink area); - the program will also suggest the type of diode that can be used in the circuit. If the program cannot select the appropriate diode from its database, then the message “No options” will be displayed, and then the diode will need to be selected independently; - in the “Capacitor” field information about the required capacitor capacity.

The program also has the ability to save calculation results into a text document (*.txt). To do this, select “Save” in the “File” menu item or use the “Ctrl+S” hotkey.

As an example, let's carry out calculations of a bridge rectifier using the following parameters: - voltage at the rectifier output - 12 volts; – current consumed by the load – 500 milliamps; – ripple factor – no more than 5 millivolts. We enter the data into the program and get:

— we need a transformer with a voltage on the secondary winding of 13.3 volts and a permissible current of at least 560 milliamps; – rectifier diodes with a permissible forward average current of at least 0.8 amperes and a reverse voltage of at least 19 volts; – the heat sink area for diodes must be at least 27 sq.cm; – the program suggests using the KTs402A diode assembly as rectifier diodes, if we do not have such an assembly, then we will have to select the diodes ourselves, for which you can use the appropriate program, for example, “ Handbook of Radio Components - TBFEdit ”; – the capacity of the smoothing capacitor must be at least 500 microfarads, but since there are no capacitors of such capacity (the closest one is 470 µF), the diagram shows a capacitor with the nearest higher capacitance – 1000 µF.

Download program:

Program for calculating a bridge rectifier (506.9 KiB, 16,590 hits)

We advise you to read: ♦ Power supplies for amateur radio devices

How to make a diode bridge with your own hands

If necessary, and if you have the necessary diodes and a soldering iron, it is not difficult to assemble a diode bridge with your own hands.

What do you need for work?

To work, you need to prepare a workplace with a socket for a soldering iron, a soldering iron with a stand, solder, rosin, tweezers, and small wire cutters. Of course, you need diodes with the required characteristics. If desired, the bridge can be assembled on a printed circuit board with ready-made tracks.

Manufacturing instructions

Illustration	Description of action
PHOTO: youtube.com	Preparation of the workplace
PHOTO: youtube.com	Soldering circuits
PHOTO: youtube.com	Instrument testing of the assembled circuit
PHOTO: youtube.com	Checking the circuit under load with a filter capacitor

Functionality check

The first check is always visual. It is checked whether the parts are installed correctly, whether the circuit is assembled correctly, and the quality of soldering. Then a test circuit with a source and a measuring device is assembled. And if this stage was successful, then you can connect the load and conduct a final check of the results of your work.

Welding Application

Any transformer or inverter contains power diodes. They are designed to rectify alternating current. To increase the efficiency, the diodes are connected in a bridge circuit, in which case both half-cycles fall on the load.

In a transformer welding machine, rectifier diodes are installed at the output of the secondary winding. Welding equipment has a step-down transformer; accordingly, the no-load voltage is significantly lower than the input voltage, so high-power and low-frequency devices are required here. B200 rectifier diodes (maximum current 200A) are suitable for this.

The welding inverter requires two rectifiers. One is located at the input of the power source. It converts alternating current 220 volts 50 Hz into direct current, which is further converted into alternating current of high frequency (40-80 kHz).

With a device power of 5 kW, the rectifier diodes should have a reverse voltage of 600-1000 V and an average forward current of 25-35 A at a frequency of 50 Hz.

The second rectifier is located after the high-frequency transformer. Here the requirements are different. The maximum forward current must be at least 200 A at a frequency of 80 kHz, and the reverse voltage must exceed the open circuit voltage (60-70 V).

In any case, diodes from the powerful category are used, with a platform for mounting a radiator, since without heat removal the device will quickly burn out.

Rectifier calculation

Rectifier calculation

Since the vast majority of power supply designs use a full-wave rectifier, the diodes of which are connected in a bridge circuit (Fig. 1), the choice of its elements will be discussed here. Calculating a rectifier means choosing the right rectifying diodes and filter capacitor, as well as determining the required alternating voltage removed for rectification from the secondary winding of the network transformer. The initial data for calculating the rectifier are: required voltage at the load (Un)

and the maximum current consumed by it
(In)
.

The calculation is carried out in this order:

1. Determine the alternating voltage that should be on the secondary winding of the network transformer:

U2 = B Un

where: Un — constant voltage at the load, V; B is a coefficient depending on the load current, which is determined from the table. 1.

0,2	0,4	0,6	0,8	1,0
IN	0,8	1,0	1,9	1,4	1,5	1,7
WITH	2,4	2,2	2,0	1,9	1,8	1,8

2. Based on the load current, determine the maximum current flowing through each diode of the rectifier bridge:

Id = 0.5 C In,

where: Id - current through the diode, A; In—maximum load current, A; C is a coefficient depending on the load current (determined from Table 1).

3. Calculate the reverse voltage that will be applied to each rectifier diode:

Uform = 1.5 Un,

where: Urev - reverse voltage, V; Un—load voltage, V.

4. Select diodes whose rectified current and permissible reverse voltage values are equal to or greater than the calculated ones.

5. Determine the capacitance of the filter capacitor:

Sf = 3200 In / Un Kp

where: Cf is the capacitance of the filter capacitor, μF; In—maximum load current. A; Un—load voltage, V; Kp is the ripple factor of the rectified voltage (the ratio of the amplitude value of the alternating component with a frequency of 100 Hz at the output of the rectifier to the average value of the rectified voltage).

For various loads, the ripple factor should not exceed a certain value, otherwise an alternating current hum will be heard in the dynamic head or loudspeaker. To power portable receivers and tape recorders, for example, the rectified voltage ripple factor is allowed within 10-3...10-2, HF and IF amplifiers - 10-4...10-3, preliminary stages of LF amplifiers and microphone amplifiers - 10-5...10 -4. If the output voltage of the rectifier is additionally stabilized by a transistor voltage stabilizer, then the calculated capacitance of the filter capacitor can be reduced by 5...10 times. Source: shems.h1.ru

Application areas of diode bridges

Diode rectifier bridges are used not only in welding units, but also in transformer devices. They are used in pulse rectifier devices. An example would be the power supply circuit of a conventional computer. Such rectifiers are used in compact fluorescent lamps; without them, energy-saving lamps do not work. A diode bridge is needed in various ballast electronic devices. They are installed in both single-phase and three-phase circuits.

Such assemblies are used in electricity meters, in control units for household appliances, which include televisions, washing machines, computers, power tools, mixers, vacuum cleaners, and refrigerators. Without them, industrial equipment circuits and cars do not work. In most cases today, instead of 1N4007 diodes, an assembly with the same characteristics MS500 is used. This diode bridge is equipped with leads located in 2.5 mm pitches. The assembly area is only 30 sq. mm. Its height is 1.6 mm.

You can assemble a diode bridge quite quickly and easily at home.

What is a car generator

A car generator is a unit that converts mechanical energy into electrical energy and performs the following functions:

provides a constant and continuous charge of the battery when the engine is running;
provides power to all systems during engine starting, when the starter consumes a large amount of electricity.

The generator is installed in the engine compartment. Using brackets, it is attached to the internal combustion engine block and driven by a drive belt from the crankshaft pulley. An electric generator is connected in an electrical circuit parallel to the battery. The battery is charged only when the electricity generated exceeds the battery voltage. The power of the generated current depends on the crankshaft speed; accordingly, the voltage increases with pulley speed with geometric progression. To prevent overcharging, the generator is equipped with a voltage regulator that regulates the amount of voltage at the output, providing 13.5-14.7V.

Diagram and operating principle of a diode bridge

Diode bridge diagram Fig. Highest operating rectification current.

With the advent of cheap semiconductor diodes, this circuit began to be used more and more often. The answer is shown in the following figure. They determined it without knowing anything about free electrons or holes.

The result is a higher degree of smoothing with the same capacitance of the filter capacitor, increasing the efficiency of the transformer used in the rectifier. If one diode in a monolithic assembly fails, the entire assembly will have to be replaced, despite the fact that the three remaining elements may be serviceable.

The pulsations are smoothed out, and the voltage becomes close to constant. Device connection diagram On electrical diagrams and printed circuit boards, a diode rectifier is indicated by a diode icon or in Latin letters.

As the name suggests, a bridge of 4 or 6 diodes is assembled. Working with both half-waves of alternating voltage, the diode bridge compares favorably with half-wave rectifiers.

Operating principle of a diode bridge

Metals are characterized by the fact that electrons in their crystal lattice almost do not stick, fly out and dangle between the atoms of the crystal for any reason, the slightest temperature, causing the nuclei of atoms in their places to vibrate slightly, knocks out the electrons completely and en masse. If you don't have a multimeter, you can use a regular voltmeter.

In this circuit, current flows from the phase with the highest potential, through the load to the phase with the lowest potential. This ripple can be slightly reduced by using a capacitor connected in parallel to the output of the diode bridge.

Its value increases and depends only on the resistance of the p- and n-regions. Rectifier design and connection diagram To date, nothing better has been invented for full voltage rectification than a conventional diode bridge. WHAT IS A DIODE BRIDGE

Principle of operation

The operating principle of this type of rectifier device is based on the property of a semiconductor diode to pass electric current in one direction and not in the other. So, if we connect the plus and minus correctly, current will flow through the device. If we swap the plus and minus positions, there will be no movement.

Alternating current differs in that during one half-cycle it moves in one direction, and during the second - in the opposite direction. And if you simply connect one diode to the circuit, then it will work “beneficially” only for one half-cycle. What if you connect the diodes so as to use both half-cycles? Thanks to this idea, bridge rectifiers appeared.

The diode bridge-rectifier circuit is quite simple and can be assembled with your own hands. It consists of four diodes connected in the form of a square. Alternating current is supplied to two opposite corners from a generator. A constant is removed from the other two opposite angles. During the first half-cycle, two diodes open, rectifying the half-wave of alternating current. During the second half-cycle, two other diodes open, converting the second half-wave. The result is a direct current output with a pulse frequency twice as high as the alternating current frequency.

Advantages and disadvantages of the scheme

To use rectified current, the pulse component must be smoothed using a filter capacitor. The higher the frequency, the better the smoothing process. Therefore, doubling the frequency in a bridge circuit is an advantage.
Full-wave rectification makes it possible to better utilize the power of the supply transformer and thereby reduce its size.

Flaws.

Double the voltage drop compared to a half wave rectifier.
Power loss due to heat dissipation is doubled. Low-dropout Schottky diodes are used to reduce losses in high-power low-voltage circuits.
If one of the bridge diodes fails, the rectifier device will work, but its parameters will differ from normal. This, in turn, can negatively affect the operation of systems powered by a rectifier.

Rectifier faults

Since the generator rectifier assembly consists of several semiconductor devices and is protected by a cover in 90% of cases, diagnostics will require electrical tools and partial disassembly of the generator. However, in some cases, the driver can hear signs of a diode bridge malfunction:

when pulsations occur (alternating voltage is supplied to the on-board network instead of direct voltage), the electric motors of some consumers can reproduce sounds by analogy with a speaker;
Most often, the drive of the power windows and stove “squeaks”, and the tone changes when the speed of these devices changes, and not the crankshaft speed.

In all other cases, malfunctions of the vehicle generator in the rectifier assembly are diagnosed exclusively by instruments. To do this, you will need a diagram for connecting the diode bridge in a specific modification of the generator, since the symptoms of a mechanical failure are completely similar to the breakdown of electrical parts.

Diagnostics of breakdowns

The rectifier assembly is assembled using various technologies - some parts are attached mechanically, small diodes are soldered into the circuit, large ones are usually pressed in. Therefore, repair of the rectifier may be required, not only if the semiconductor elements fail, but also if they are installed incorrectly on the “horseshoe” of the heat sink plate.

The diagnostic technique is as follows:

the back cover is removed from the generator to provide access to the diodes;
the plate is supplied with a “–” wire from the battery, it is pressed against the housing on the generator, one wire of the lamp touches the diode at the point where the stator winding is connected, the second – to the “+” of the battery, if there is a breakdown, the light will light up;
The tester is set to 1 kOhm ohmmeter mode; if you swap the multimeter probes, the readings should change from 0 to 400 - 800 Ohms in different directions.

Read more: I charge the battery and it boils

In most cases, the diode bridge burns when moisture penetrates.

How to calculate and select a diode bridge based on power

The maximum ripple voltage present in the full-wave rectifier circuit is determined not only by the value of the smoothing capacitor, but also by the frequency and load current and is calculated as:

Rectifier Bridge Ripple Voltage

Ripple Voltage Formula

Where: I is the DC load current in amperes, ƒ is the ripple frequency or twice the input frequency in Hertz, and C is the capacitance in Farads.

The main advantages of a full-wave bridge rectifier are that it has lower AC ripple for a given load and a smaller reservoir or smoothing capacitor than an equivalent half-wave rectifier. Therefore, the fundamental frequency of the ripple voltage is twice the AC frequency (100 Hz), where for a half-wave rectifier it is exactly equal to the supply frequency (50 Hz).

The amount of ripple voltage that is superimposed on top of the DC supply voltage by the diodes can be virtually eliminated by adding a greatly improved π filter (pi filter) to the output terminals of the bridge rectifier. This type of low-pass filter consists of two smoothing capacitors, usually of the same value, and an inductor or inductor across them to introduce a high-impedance path into the variable ripple component.

Bridge rectifier

Another, more practical and cheaper alternative is to use an off-the-shelf three-pole voltage regulator IC such as the LM78xx (where xx denotes the rated output voltage) for positive output voltage, or its inverse equivalent, LM79xx for negative output voltage, which can reduce ripple by more than 70 dB (datasheet), providing a continuous output current of more than 1 amp.

Many circuits with this technology are built with a bridge rectifier. Bridge rectifiers convert AC to DC using their diode system made of semiconductor material, either in a half-wave method, which rectifies one direction of the AC signal, or in a full-wave method, which rectifies both directions of the AC input signal.

Diode bridge GBL10

Semiconductors are materials that allow current to pass because they are made of metals such as gallium or metalloids such as silicon that are contaminated with materials such as phosphorus as a means of controlling the current. You can use a bridge rectifier for a variety of applications for a wide range of currents.

Bridge rectifiers also have the advantage of delivering more voltage and power than other rectifiers. Despite these advantages, bridge rectifiers suffer from the need to use four diodes with additional diodes compared to other rectifiers, causing a voltage drop that reduces the output voltage.

Use and application

Today, bridges are widely used in all cases where direct current is used - from mobile phones to cars. The industry produces a large number of rectifier devices made using a bridge circuit. Therefore, choosing the right bridge is not difficult, provided you have a clear understanding of why it is being purchased and what functions it will perform.

Structurally, rectifiers can be made on separate diodes or as a single unit. In the first case, if one of the diodes is damaged, you can replace it. To do this, you need to know how to ring a diode bridge. The test is carried out in the form of a sequential search of all diodes to pass current in the forward and reverse directions. As an indicator, you can use either a regular light bulb or a device that measures current or resistance.