Everyone knows that the bridge can be built across the river, across the road, through a ravine. But not everyone has heard the expression "diode bridge." What is it and why do we need such a bridge?
Figure 1. Standard diode bridge circuit.
What is a diode bridge
The property of diodes to pass voltage in one direction only is known from the school program in physics. The diode bridge (Fig. 1) consists of 4 diodes. This map shows the soldering scheme of the parts. Its main purpose is to convert alternating voltage into direct voltage. At first, these circuits were assembled on radio tubes. It was expensive and difficult. Nowadays, semiconductor products have become quite cheap, so the given constructions are soldered with their use. A circuit assembled using diodes (Fig. 2) can be supplemented with filters assembled using polar capacitors, a choke and a zener diode.
Figure 2. Diagram of parallel connection of diode bridges for large currents of the welding apparatus.
The finished product allows you to:
- receive a constant voltage at the output;
- Avoid bias current that may appear in the transformer that supplies the circuit;
- increase the efficiency of the transformer and make it smaller.
The circuit can be assembled from individual diodes or be a monolithic structure of various shapes and sizes. It is often called an assembly. Diode assembly is preferable. It usually has smaller sizes.
All diodes inside have exactly the same parameters. It is much simpler to mount such a construction in the general scheme of the device. The lack of design - in the case of combustion of any diode you need to change the entire assembly. In the circuit consisting of individual diodes, in this case, only the burned element changes.
The principle of operation of the diode bridge.
For the manufacture of diodes and bridges on their base, various materials are used. In the marking of parts there are letters and numbers that indicate:
- "G" - germanium and its compounds;
- "K" - silicon and compounds;
- "A" - gallium;
- "And" - indium;
- "C" - ready bridge.
The numbers usually indicate the product development number. All this applies to products manufactured in the USSR and Russia.Back to table of contents
We collect the diode bridge
The rectifier circuit of the welding machine with a capacitor.
The diode bridge is the most common radio component in the power supply unit for various devices. It performs the functions of a rectifier, producing a DC voltage converted from AC. The product can be assembled from individual diodes. The most common ones are 1N4007. All of them are designed for voltages up to 1000 V and currents up to 1 A. The assemblies usually have directions to which wires to connect. For self-assembly schemes for use in the welding unit can do the following:
- Select the type of future product.
- Calculate it.
- Make a cooling radiator.
- Fix the finished diode structure on the radiator.
Diagram of the use of a diode bridge in a transformer.
The product can be assembled from individual diodes, you can use a monolithic assembly. Individual diodes, their parameters can be calculated using the following example: you need a bridge for a voltage of 1000 V, 4 A. Then its full power will be 1000 × 4 = 4 kW. Through each individual diode flows approximately 70% of the total current. In the specific case at a current of 4 A, this will amount to 3 A.
During the operation of the circuit, the diode structure will necessarily heat up. To cool it you need a good cooling radiator. For a welding machine, it can be made from aluminum sheet with an area of approximately 800 sq. Cm. On it you need to drill the necessary holes for fastening the fabricated structure, cut the thread. The finished assembly should be mounted on a homemade radiator with M6 bolts. The space for the product can be greased with heat-conducting paste KPT-8. All wires to the diode bridge are attached by soldering. Diodes can use brand B-200. They operate at currents up to 200 A.Back to table of contents
Diode Bridge Applications
Diode rectifier bridges are used not only in welding units, in transformer devices. They are used in pulsed rectifier devices. An example is the power supply circuit of a familiar computer. Such rectifiers are used in compact fluorescent lamps, energy-saving lamps do not work without them. We need a diode bridge in various control 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, do not work the scheme of industrial equipment, cars. In most cases, today, instead of diodes 1N4007, an assembly with the same MS500 characteristics is used. This diode bridge is equipped with leads located in 2.5 mm pitch. Assembly area of 30 sq. M. Its height is 1.6 mm.
The devices with high temperature use B250S2A series assemblies, they are capable of operating at temperatures up to 125 °.
To assemble a diode bridge can be quite quickly and simply at home.
To do this, take 4 diodes, solder the cathodes of a pair of diodes, the anodes of another pair. On the soldering of the cathodes, the positive contact of the circuit will be located; An alternating mains voltage is supplied to the remaining terminals. For full complexion, a polar capacitor with a parallel discharge resistance will be soldered at the output. Such devices can be inserted into the circuits of many electronic devices.