The device, the principle of operation and the diode bridge rectifier circuit

The alternating electric current is converted into a constant pulsating one due to the use of special electronic circuits - diode bridges. Diode bridge rectifier circuit is divided into 2 versions: single-phase and three-phase.

In the operation of the rectifier, the main element is the diode. Structurally, it is a plate of a semiconductor crystal with two zones of different conductivity. A feature is the one-sided flow of electric current, depending on the direction of flow.

The design and operation of the rectifier diode is based on the features of the pn junction between the semiconductor zones. Its resistance depends on the polarity of the external voltage. In one case it is large, in another case it is insignificant.

Single-phase diode bridge

When the input is an alternating sinusoidal voltage, in each half-cycle the current passes through one pair of diodes, and the other is closed. As a result, a pulsating voltage is generated at the output of the diode rectifier bridge circuit, the frequency of which is two times higher than at the input.

Three-phase bridge circuit

Diode half-bridge rectifiers are used in this scheme. The output voltage here is obtained with smaller pulsations.

How to smooth the ripple when straightening the power?

The quality of the rectified voltage decreases with an increase in its ripple. To reduce it, elements are used that store energy when it comes from the rectifier and give up when its supply stops.

On the diode bridge rectifier circuit with a capacitor, the latter is connected in parallel with the load. Its capacity is selected depending on the load current. When the pulse is applied, the capacitor is charged. Between the impulses (when there are none), the voltage from it is given to the load.

As a result of smoothing, the output voltage of the filter becomes larger and approaches the value of the amplitude of the rectified value.

The ideal voltage at the filter output can not be obtained due to the discharge of the capacitor between pulses. Usually such pulsations are permissible. They can be reduced by increasing the capacity of the capacitor.

If an inductor is used for smoothing, it is connected in series with the load. The combined filter circuits include chokes and capacitors.

Diode bridge constructions

The simplest device of the bridge is performed by soldering individual diodes. The industry produces monolithic structures, which are smaller in size and cheaper. In addition, they choose diodes with similar characteristics, which allows them to work with the same heat. This improves the reliability of the diode bridge rectifier circuit.

The advantage of diode bridges from individual elements is the possibility of repair, when one of them will fail. The assembly has to be replaced completely. Faults in it are rare, because the elements are correctly matched.

Rectifier power supply

Devices consuming a large current are usually powered from the 220 V network. Directly, devices are not connected, since the voltage for the electronic circuits is small and the current is constant. Then use a network adapter.

Voltage is reduced by a transformer, which also creates a galvanic isolation between the primary and secondary supply circuits. This reduces the risk of electric shock and protects the equipment when a short circuit occurs in the circuit.

Modern adapters in most cases work with a simplified transformerless design without galvanic isolation, where excess voltage is absorbed on the capacitor.

Diode bridge circuit 12 volts: instruction and assembly

The power supply consists of two modules, where the first is a step-down transformer, and the second is a diode bridge that converts one type of voltage to another.

A suitable transformer is selected. The primary winding is found using a tester. Its resistance should be the greatest. By means of a multimeter in the resistance measurement mode, the required ends are located. Then there are other pairs and markings are made.

The primary winding is 220 V. Then the tester is switched to the AC voltage measurement mode and the voltage is measured on the remaining windings. It is necessary to select or wind one by 10 V. It is important that the voltage is not 12 V, since after the capacitive filter it is increased by 18%.

The transformer is selected to the correct power, after which the reserve is taken up to 25%.

4 diode are twisted into the diode bridge and the ends are propaited. Then the circuit is connected, the output is connected to a capacitor of 25 V and 2200 μF (electrolyte) and checked in operation.

Transformerless Diode Bridge 24 Volt Diode Bridge

In radio amateur practice, low-power power supplies without transformers are widely used.

Power 220 V is supplied via the ballast capacitor C1. The rectifier consists of diodes VD1, VD2 and zener diodes VD3, VD4. To eliminate current surges across the bridge, when the power is connected in series with the capacitor, a current limiting resistor of 50-100 ohms is installed. To discharge the capacitor when the circuit is not working, a 150-300 kΩ resistor is connected in parallel to it.

At the output of the circuit, a smoothing capacitor with a capacity of 2000 μF is installed.

The absence of galvanic connection creates the danger of electric shock.

Application

The applications of the diode bridge are extremely wide and varied:

• Lighting devices (LED and fluorescent lamps);
• Electric power metering devices;
• Power supply units for electronic equipment;
• Industrial power supplies, controls and chargers.

How to choose diodes for manufacturing a diode bridge?

The main selection criteria are the voltage and current at which the diode does not overheat. With a direct connection, a voltage of about 0.6 V falls on it, since it has an internal resistance. The reverse voltage, which the diode can withstand, without entering into a mode of thermal and electric breakdown, has a certain limit. If it is designed for 220 V, then a reserve of at least 25% is taken. But it is better to take it large enough to protect against accidental power surges in the network.

Current is also taken with a margin. If necessary, a cooling radiator is provided.

For a correct choice use the reference table of diodes and diode bridges.

Manufacturers of diode bridges

Among the elements for lighting equipment stand out rectifiers series 1N4007 and MS250 produced by Diotec. They are rated for voltage up to 1000 V. In the first case, the diode bridge circuit consists of 4 diodes placed on the printed circuit board, and in the second it is presented in the form of a compact assembly. Although the 1N4007 series is reliable in operation, the MS250 assembly saves weight and space. Despite this, the demand for the 1N4007 series remains high, as the price has fallen so much that it is mainly determined by the cost of copper terminals.

The technology of manufacturing MS series diode bridges continues. Now all 4 crystals of the bridge are installed together, which increases its heat resistance due to the uniformity of the parameters.

The reliability of the rectifiers falls with the rise in the temperature of the surrounding air. This problem is solved by the device of the B250S2A series, designed for a current of 2.3 A and transmitting 0.7 A at 125 ° C.

Most manufacturers buy diodes, after which they assemble ready-made rectifiers. Diotec deals with the entire production cycle, from making crystals to assembling and packaging.

Another leading world company - IRF - has unique technologies to reduce the dimensions of parts, improve heat transfer, improve the efficiency of semiconductor technology. It is the only one producing components for the entire energy conversion cycle.

Conclusion

Diode bridge rectifier circuit is used in all electronic equipment. To apply follows full-wave rectifiers, the characteristics of which are much better than single-period rectifiers. You can check any of them yourself by calling each diode.