In the overwhelming majority of power supplies to straighten the AC electrical current, diode bridges are used. Consider the diode bridge, the scheme includes only 4 diodes. On the conceptThe diode bridge is indicated as a square rotated at 45 degrees in the center of the square on one of the diagonals of the Diode Diode, the cathode is closer to the positive output of the bridge, the anode is closer to the negative bridge output. The remaining two vertices of the square are inputs of alternating voltage.
The diagram of the bridge is enough to remember that two diodes come to "+" from each input, the reception of the anode is connected to the input, and the cathode on the output. Also with a negative output, only diodes are connected to the output.
Imagine that an alternating voltage is submitted to the input of the diode bridge and the current potential is present on the upper figure in the figure, the VD2 and VD3 diodes will open as a positive voltage is applied to them (in the figure the current path is shown in red), and VD1 And VD4 will be locked with reverse voltage. With the reverse polarity of the input voltage, the current flows from the bottom input via VD4, the load and VD1 (in the figure, the current path is shown in blue), and VD2 and VD3 will be locked with reverse voltage.
It turns out a positive output will be connected to the input of the diode bridge, on which this moment There is a positive potential, and a negative output with the entrance on which the negative potential.
Three phase diode bridge scheme
The diode bridge considered by us is used for single-phase straightening, and is called a single-phase bridge. To straighten an alternating electric current in three-phase networks use a three-phase diode bridge.
It consists of 6 diodes, on a pair of diodes for each phase. In this scheme, the current flows from the phase with the greatest potential, through the load to the phase with the lowest potential. The remaining phase is not connected to anything. If two diodes of four were conducted in a single-phase bridge, then a current of 2 diodes is carried out here, and 4 at the same time locked. 
Diode bridges are produced as complete components, but if there is no such detail, you can use 4 separate diode on the diode bridge circuit.
For surface assembly boards, it is convenient to use dual diodes. For example, from two diode assemblies of Bat54S or Bav99, a full-fledged diode bridge is obtained.
Often, the use of two assemblies of two diodes is cheaper than using a diode bridge of four diodes in one case or four diodes separately.
Most power stations produces alternating current. This is due to the feature of the generator design. The exception is only the solar panels from which the constant current is removed.
In general, the choice between constant and alternating current from the point of view of production, transportation and consumption is the struggle of contradictions.
It is more convenient to produce (produced in power plants).
Transport cost-effective current. Change semi-dimensions of alternating voltage leads to losses.
From the point of view of transformation (reduction of voltage values) it is more convenient to operate with alternating current. Principle of operation Transformers are built on a pulsating or alternating voltage.
Most electricity consumers (we are talking about devices) operate on a constant current. Electroschemes cannot work with alternating voltage.
As a result, we have the following picture:
A variable current with a voltage of 220 volts comes to the socket. And all the home electrical appliances (with the exception of those that contain powerful electric motors and heating elements) dC.
Inside most home equipment there are power supplies. After lowering (transformation) of the voltage value, it is necessary to convert a current from the variable to the constant one. The basis of such a scheme is the diode bridge.
Why do you need a diode bridge?
Based on the definition, the alternating current with a certain frequency (in the household power grid 50Hz) changes its direction, with an unchanged value.
Important! Since we know that a polar voltage is needed to feed most of the power supply - in the power supply blocks, an AC is replaced by a permanent.
It happens in two or three stages:
Using a diode assembly, alternating current turns into a pulsating. This is already a straightened schedule, however, for the normal functioning of the diagram of such a quality of nutrition is not enough.
For smoothing pulsations, a filter is installed after the bridge. In the simplest case, this is an ordinary polar capacitor. If necessary, increase quality - throttle is added.
After conversion and smoothing, it is necessary to provide a constant value of the operating voltage.
For this, voltage stabilizers are installed in the third stage.
Nevertheless, the first element of any power supply is a diode bridge.
It can be made from both separate parts and in mono housing.
The first option takes a lot of space and more difficult in installation.
There are advantages:
This design is inexpensive, it is easier to diagnose, and in case of failure of one element, only it changes.
The second design is compact, the errors in the installation are excluded. However, the cost is somewhat higher than that of individual diodes and it is impossible to repair one element, you have to change the entire module.
The principle of operation of a diode bridge
Recall the characteristics and purpose of the diode. If you do not go into technical details - it misses electricity In one direction, and closes his path in the opposite.
This property is already enough to assemble the simplest rectifier on one diode.
The element is simply turned on in the circuit sequentially, and each second pulse of the current coming in the opposite direction is cut off.
This method is called single-alterogenic, and he has many drawbacks:
Very strong ripple, between half-periods there is a pause in the flow of current equal to the length of half of the sinusoids.
As a result of cutting off the lower waves of sinusoids, the voltage decreases twice. For accurate measure The decrease is greater, since there are losses in diodes.
The ability to reduce the voltage in half when it is straightened, has found an application in housing and communal services.
The tenants of apartment entrances, the charter change constantly burning light bulbs - equip them with diodes.
When you turn on sequentially, the brightness of the glow and the lamp "lives" is much longer.
True, strong flicker tiring eyes, and such a lamp is suitable only for duty lighting.
To reduce losses, the connection of four elements is applied.
Two-wire diode bridge, work scheme:
In whatever direction, the alternating current on the introductory contacts, the output of the diode bridge provides unchanged polarity on its output contacts.
The pulsation frequency of such a compound is exactly two times higher than the frequency of the AC at the input.
Since the shoulders of the bridge cannot simultaneously pass the current in both directions - stable protection of the scheme is ensured.
Even if you have burned the diode bridge in your device - short circuit or voltage jump will not.
The reliability of the bridge circuit is tested for decades. Input overvoltage protection is guaranteed by a transformer.
The overload saves the output stabilizer. Persons a diode bridge only in the case of using defective parts, or in a car, where the scheme is subjected to constant loads.
How does the diode bridge work with minimal voltage?
The voltage drop in the diode bridge is up to 0.7 volts. When using a conventional element base in low-voltage schemes, sometimes the voltage drop is up to 50% of the ratio of the power supply. Such an error is unacceptable.
To ensure the operation of power supplies with a voltage of 1.5 volts to 12 volts - Schottky diodes are used.
With direct flow flow, the voltage drop on one crystal is not more than 0.3 volts. We multiply into four elements in the bridge - it turns out quite acceptable loss value.
In addition, if the Schottky Diode Bridge is on the interference level - you will get a value unattainable for silicon P-N diodes.
Another advantage due to absence of p-n Transition - the ability to work at high frequency.
Therefore, rectifiers over high-frequency voltage make exclusively on diodes of this type.
However, Schottky diodes have disadvantages.. When exposed to the return voltage, even if short-term - the element fails.
Checking a diode bridge by a multimeter shows that it is this reason that has irreversible consequences.
Ordinary germanium or silicon element with p-N transition They are restored after the ransom.
Therefore, the bridges on Schottki diodes are used only in low-voltage power supplies and in the presence of reverse voltage protection.
What if there are suspicions of the breakdown of the bridge?
The rectifier is assembled on a conventional element base, so we will tell you how at home to check the diode bridge multimeter.
The illustration shows how the current on the bridge flows. The test principle is the same as when checking single diodes.
We look at the directory, which conclusions of the module correspond to the variable input or polar exit - and perform a call.
How to ring the diode bridge without falling out of the scheme?
Since the current in the opposite direction through the diode does not flow, incorrect test results are talking about the sample of the bridge.
Removing the bridge is not necessary, the remaining elements of the power supply do not affect the measurement.
Outcome: any of you can create a diode bridge yourself and repair it in the event of a breakdown. It is enough to have elementary skills in electrical engineering.
Watch the video: as a multimeter to check the diode bridge of the generator of your car.
A detailed story about how to check the diode bridge by a multimeter in this video story
This charger I did to charge the car batteries, the output voltage is 14.5 volts, the maximum charge current is 6 A. But they can also charge other batteries, such as lithium-ion, since the output voltage and output current can be adjusted widely. The main components of the charger were bought on Aliexpress website.
These are these components:
The electrolytic capacitor of 2200 μF is still required to 50 V, the transformer for the TC-180-2 charger (how to disperse the TC-180-2 transformer Look at B), wires, a power plug, fuses, a radiator for a diode bridge, crocodiles. The transformer can be used by another, with a power of at least 150 W (for charging current 6 A), the secondary winding must be calculated for the current 10 A and produce a voltage of 15-20 volts. The diode bridge can be dial from individual diodes designed for current of at least 10a, for example D242A.
The wires in the charger must be thick and short. The diode bridge must be fixed on a large radiator. You need to increase the DC-DC radiators of the converter, or use the fan to cool.
Assembling charger
Connect the cord with the network fork and the fuse to the primary winding of the TC-180-2 transformer, set the diode bridge to the radiator, connect the diode bridge and the secondary winding of the transformer. Sold down the capacitor to the positive and minus conclusions of the diode bridge.
Connect the transformer to the 220 volt network and make measurements of the voltage multimeter. I got the following results:
- AC voltage at the outlook outlook 14.3 volts (voltage in 228 volts).
- Permanent voltage after a diode bridge and a capacitor 18.4 Volt (without load).
Guided by a diagram, connect with a diode DC-DC bridge down converter and a voltammermeter.
Setting the output voltage and charging current
On the DC-DC board of the converter are installed two strong resistorOne allows you to set the maximum output voltage, other you can set the maximum charging current.
Turn on the charger to the network (nothing is connected to the output wire), the indicator will show the voltage at the device output, and the current is zero. Set the voltage potentiometer at the output of 5 volts. Close the output wires, the current potentiometer, set the short circuit current 6 A. Then eliminate the short circuit, disconnecting the output wires and voltage potentiometer, set the output of 14.5 volts.
This charger is not afraid of a short circuit at the exit, but when stirring can fail. To protect against cakes, a powerful Schottky diode can be installed in the break of the plus wire of the battery. Such diodes have a small voltage drop with direct inclusion. With such protection, if you confuse polarity when connecting the battery, there will be no current. True, this diode will need to be installed on the radiator, since it will flow a long current through it when charging.
Suitable diode assemblies are used in computer blocks Nutrition. In such an assembly there are two Schottky diodes with a common cathode, they will need to be replenished. For our charger, diodes are suitable with a current of at least 15 A.
It should be borne in mind that in such assemblies the cathode is connected to the housing, so these diodes need to be installed on the radiator through an insulating gasket.
It is necessary to adjust the upper voltage limit once again, taking into account the voltage drop on protection diodes. For this, the voltage potentiometer on the DC-DC board of the converter must be set 14.5 volts measured by a multimeter directly on the output terminals of the charger.
How to charge battery
Wipe the battery with a rag moistened in soda solution, then dry. Remove the plugs and control the level of the electrolyte, if necessary, draw distilled water. Corks during charge must be twisted. Inside the battery should not fall garbage and dirt. The room in which the battery charges should be well ventilated.
Connect the battery K. charger And turn on the device to the network. During the charge, the voltage will gradually grow to 14.5 volts, the current will decrease with time. The battery can be conditionally charged when the charging current falls to 0.6 - 0.7 A.
The diode is a semiconductor unit with a different conduction determined by the applied voltage. It has two conclusions: cathode and anode. If direct voltage is supplied, that is, on the anode in comparison with the cathode, the potential is positive, the unit is open.
If the voltage is negative, it closes. Such a feature found use in electrical engineering: the diode bridge is actively used in the welding business to straighten the AC and improving the quality of welded operations.
How to make a rectifier with your own hands?
If in the presence of the wizard there are components, it is quite realistic to make a homemade welding rectifier. Subject to all the recommendations of the specialists, it is guaranteed to provide the process of manual arc welding of constant current, but it will be necessary to apply an electrode with a coating.
It is also permissible to use wire without coating, but only if there is great experience in welded issues. For an inexperienced welder, it will be practically unrealistic to cope with it.
Diode bridge for welding machine.
The coating when moltening the electrode prevents the penetration of the components of the air into the molten metal of the welded joint. Without it, the contact of the metal in the molten form with nitrogen and oxygen will reduce the strength properties of the seam by making it fragile and porous.
First, you will need to choose or wind the lowering transformer with the required parameters. Collect the transformer before connecting the diode bridge.
If the path is selected independent manufacture The device is important to correctly calculate its elements, including:
- parameters of the magnetic pipeline;
- actual number of turns;
- sizes of the cross section of tires, wires.
On a note! Calculations for the manufacture of transformers are carried out according to a single technique, so this task It does not represent difficulties even for an inexplicable welder with school knowledge of electricity.
In work, do not do without LEDs: they need as current conductors in one single direction. The simplest diode, created by the bridge scheme, is mounted on the radiator for the purpose of heat exchange and cooling.
Powerful diodes for the welding machine, according to the type VD-200, are isolated during the operation quite large volume of thermal energy. To ensure the incidental current characteristic, the throttle will be needed in the chain sequentially.
Active variable resistance In such a scheme, will provide a welder to smoothly adjust the welding current. Next, one pole must be connected to a welded wire, and the second to the working object.
The electrolytic capacitor as part of the circuit is necessary as a smoothing filter to reduce ripples.
The winding of the rheostat is easy on its own, but for such a task, a ceramic core and a nickel or nichrome wire will be required. The current wire diameter will determine the adjustable current of the welded operation.
The calculation of the resistance of the rheostat should be carried out by taking into account the resistivity of the electrode, its cross section and the total length.
Electrical welding diagram with diode bridge.
The step of adjusting the current for welding depends on the diameter of the turns. If you correctly assemble the listed parts into a single unit, the welding process will be accompanied by a constant current. Will not be superfluous and the installation of a resistor impeding short closure When working.
It can occur when the wire is tapping a metal without an arc ignition. If at this time there is no resistance on the condenser, it will instantly discharge, a click will occur, the electrode will break or stick to the metal.
In the presence of a resistor, you can smooth out the discharges on the condenser, make a fault of the electrode easier and soft. Manufacture of the apparatus for straightening the welded current with their own hands will create the most accurate and durable welds .
RESULTS
The diode bridge for the welding machine converts alternating current into a constant, which allows you to improve the quality of welded connections. Such a device can be purchased in finished video Or create your own hands, following the advice voiced in the article.
The phrase "diode bridge" is formed from the word "diode". Consequently, the diode bridge should consist of diodes, but they must be connected to each other in a specific sequence. Why is it important we will just talk in this article.
Designation in scheme
The diode bridge in the diagrams looks like:
Sometimes in the schemes it is designated like this:
As we see, the scheme consists of four diodes. In order for it to work correctly, we must properly connect the diodes and correctly apply alternating voltage on them. On the left we see two icons "~". We supply alternating voltage to these two outputs, and remove constant voltage from other two conclusions indicated by the "+" and "-" icons. The diode bridge is also called a diode rectifier.
Principle of operation
To straighten the alternating voltage to constant, you can use one diode for straightening, but not desirable. Let's look at the drawing, how it all will look like:
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The diode cuts off the negative half-wave of alternating voltage, leaving only positive that we see in the figure above. The whole charm of this novel scheme is that we get a constant voltage from the variable. The problem lies in the fact that we lose half the power of alternating voltage. It cuts a diode.
To correct this situation, a diode bridge circuit was invented by the great minds. The diode bridge "turns" the negative half-wave, turning it into a positive half-wave, thereby maintaining power.
At the outlet of the diode bridge, a constant pulsating voltage with frequent 100 hertz appears. This is twice as bigger than the frequency of the network.
Practical experiences
To begin with, take a simple diode.
Cathode can be easily recognized on a silver strip. Almost all manufacturers show a cathode with a strip or point.
So that our experiments were safe, I took a lowering, which from 220V makes 12V.
To the primary winding with a cling of 220 volts, with a secondary winding, remove 12 volts. Showed a little more, since there is no load on the secondary winding. The transformer works on the so-called "idle".
3.3x5 \u003d 16.5V - it maximum value Voltage. And if you divide the maximum amplitude value to the root of two, then we get somewhere 11.8 volts. That's what it is . Oscilloscope is not lying, everything is OK.
I repeat once again, it was possible to use 220 volts, but 220 volts are not a joke, so I lowered an alternating voltage.
We solder to one end of the secondary winding of the transformer our diode.
We cling again oscilloscope
We look at the oscillogram
And where bottom part Images? It cut a diode. He left only the upper part, that is, that positive.
We find three more such diodes and solder diode bridge.
We cling to the secondary winding of the transformer according to the diaper bridge.
From two other ends, we remove the constant pulsating voltage of the probe of the oscilloscope and look at the oscillogram
Here, now order.
Types of diode bridges
In order not to bother with diodes, the developers all four diode were accommodated in one case. As a result, it turned out a very compact and convenient radio element - a diode bridge. I think you will guess where imported, and where is Soviet))).
For example, the Soviet diode bridge shows the contacts to which the variable voltage should be supplied with the "~" icon, and the contacts from which the constant pulsating voltage of the "+" and "-" icon should be removed.
There are many types of diode bridges in different buildings
There is even a car diode bridge
There is also a diode bridge for three-phase voltage. It is assembled along the so-called Larionov scheme and consists of 6 diodes:
Basically, three-phase diode bridges are used in power electronics.
As you might notice, such a three-phase rectifier has five conclusions. Three outputs on the phases and from two other conclusions we will remove constant pulsating voltage.
How to check the diode bridge
1) The first method is the easiest. The diode bridge is checked by the integrity of all its diodes. To do this, it is nicknamed every diode by a multimeter and see the integrity of each diode. How to do it, read
2) the second method is 100%. But this will require an oscilloscope, or a lowering transformer. Let's check the imported diode bridge. To do this, cling two of his contact to variable tension With the icons "~", and from two other contacts, with "+" and "-" remove the testimony using an oscilloscope.
We look oscillogram
So, the imported diode bridge is working.
Summary
The diode bridge (rectifier) \u200b\u200bis used to convert alternating current to permanent.
The diode bridge is used almost in all radio equipment, which "eats" voltage from the network variable, be it a simple TV or even charging from a cell phone.