Alternating electric current is converted into a constant pulsating current due to the use of special electronic circuits - diode bridges. The rectifier diode bridge 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 semiconductor chip plate with two zones of different conductivity. A feature is the one-way transmission of electric current, depending on the direction of flow.
The device and operation of the rectifier diode are based on the features of the pn junction between the zones of the semiconductor. Its resistance depends on the polarity of the external voltage. In one case it is great, in the other - 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 rectifier diode bridge circuit, the frequency of which is two times higher than at the input.
Three phase bridge circuit
This circuit uses half-bridge diode rectifiers. The output voltage here is obtained with less ripple.
How to smooth ripple when rectifying power?
The quality of the rectified voltage decreases with increasing ripple. To reduce it, elements are used that accumulate energy when it comes from the rectifier and give it away when it stops supplying.
In the rectifier diode bridge circuit with a capacitor, the latter is connected in parallel with the load. Its capacity is selected depending on the load current. When a pulse is applied, the capacitor charges. Between pulses (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 magnitude of the amplitude of the rectified value.
The ideal voltage at the filter output cannot be obtained due to the discharge of the capacitor between pulses. Usually such ripples are permissible. They can be reduced by increasing the capacitance of the capacitor.
If an inductor is used for smoothing, it is connected in series with the load. Combined filter circuits include chokes and capacitors.
Diode bridge designs
The simplest bridge device is made by soldering individual diodes. The industry produces monolithic structures that are smaller in size and cheaper. In addition, diodes with similar characteristics are selected in them, which allows them to work with the same heating. This increases the reliability of the rectifier diode bridge circuit.
The advantage of diode bridges made of individual elements is the possibility of repair when one of them fails. The assembly has to be replaced completely. Malfunctions in it rarely occur, since the elements are correctly selected.
Rectifier Power
Devices that consume a large current are usually powered by a 220 V network. They do not directly connect devices, since the voltage for electronic circuits is small and the current is constant. Then apply the network adapter.
The voltage is reduced using a transformer, which also creates a galvanic isolation between the primary and secondary supply circuits. Due to this, the risk of electric shock is reduced and the equipment is protected when a short circuit appears in the circuit.
Modern adapters in most cases operate according to a simplified transformerless circuit without galvanic isolation, where excess voltage is absorbed on the capacitor.
Diagram of a 12-volt diode bridge: instructions and assembly
The power supply unit 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 located with the help of a tester. Her resistance should be the greatest. By dialing with a multimeter in the resistance measurement mode, the necessary ends are found. Then other pairs are found and marking is done.
220 V is supplied to the primary winding . Then the tester is switched to the AC voltage measurement mode and the voltage across the remaining windings is measured. You should choose or wind one at 10 V. It is important that the voltage is not 12 V, since after a capacitive filter it increases by 18%.
The transformer is selected for the required power, after which a margin of 25% is taken.
4 diodes are twisted into a diode bridge and the ends are soldered. Then the circuit is connected, a 25 V and 2200 uF capacitor (electrolyte) is connected to the output and checked in operation.
Transformerless 24V rectifier diode bridge circuit
In amateur radio practice, low-power power supplies without transformers are widely used.
220 V power is supplied through a C1 ballast capacitor. The rectifier consists of diodes VD1, VD2 and zener diodes VD3, VD4. To eliminate inrush currents through the bridge, when a power is connected in series with a capacitor, a current limiting resistor with a resistance of 50-100 Ohms is installed. To discharge the capacitor when the circuit is not working, a 150-300 kΩ resistor is connected to it in parallel.
At the circuit output, a smoothing capacitor with a capacity of 2000 microfarads is installed.
Lack of galvanic coupling creates the risk of electric shock.
Application
The scope of the diode bridge is extremely wide and diverse:
- lighting devices (LED and fluorescent lamps);
- electricity metering devices;
- power supplies for electronic equipment;
- industrial power supplies, controls and chargers.
How to choose diodes for making a diode bridge?
The main selection criteria are voltage and current, at which the diode does not overheat. With direct connection, a voltage of about 0.6 V drops on it, since it has an internal resistance. The reverse voltage that the diode can withstand without entering the thermal and electrical breakdown mode has a certain limit. If it is designed for 220 V, then a margin of at least 25% is taken. But it is better to take it large enough to protect against accidental power surges.
Current is also taken with a margin. If necessary, a cooling radiator is provided.
For the right choice, use the reference table of diodes and diode bridges.
Diode Bridge Manufacturers
Among the elements for lighting technology, rectifiers of the 1N4007 and MS250 series manufactured by Diotec stand out. They are designed for voltages up to 1000 V. In the first case, the diode bridge circuit consists of 4 diodes placed on a printed circuit board, and in the second it is presented in the form of a compact assembly. Although the 1N4007 series is reliable, the MS250 assembly saves weight and footprint. Despite this, demand for the 1N4007 series remains high, as the price has fallen so much that it is determined mainly by the cost of copper output.
The manufacturing technology of MS series diode bridges continues. Now all 4 bridge crystals are installed together, which increases its heat resistance due to the uniformity of parameters.
The reliability of the rectifiers decreases with increasing ambient temperature. This problem is solved by the B250S2A series device, designed for a current of 2.3 A and transmitting 0.7 A at 125 ° C.
Most manufacturers buy diodes, and then assemble ready-made rectifiers. Diotec is involved in the entire production cycle, from crystal manufacturing to assembly and packaging.
Another leading global company - IRF - has unique technologies for reducing the dimensions of parts, improving heat transfer, and increasing the efficiency of semiconductor technology. It is the only one producing components for the entire energy conversion cycle.
Conclusion
The rectifier diode bridge circuit is used in all electronic equipment. Two-half-wave rectifiers should be used, the characteristics of which are much better than single-period ones. You can check any of them yourself by ringing each diode.