The bridge rectifier is widely used to provide full wave rectification and it is possibly the most widely used circuit for this.
Using four diodes the bridge rectifier the circuit has a distinctive format with the circuit diagram based on a square with one diode on each leg.
Bridge rectifier circuits
A diagram of the basic bridge rectifier circuit has a bridge rectifier block at the centre. This consists of a bridge circuit which includes four diodes. These can be individual diodes, or it is also easy to obtain bridge rectifiers as a single component. Low current bridge rectifiers can be free standing, but higher current versions are often designed for mounting on a heat sink.
The bridge rectifier full wave rectifier has the advantage over the full wave rectifier using a centre tapped transformer that there is no centre tapped transformer requirement and that the both halves of the cycle are used in the winding.
To see how the bridge diode full wave rectifier operates it is useful to see the current flow.
The bridge rectifier components can come in a variety of forms. They can be made using discrete diodes. A ring of the four diodes can easily be made either on a tag or as part of a printed circuit board. Care must be taken to ensure that the diodes are sufficiently ventilated as they can dissipate heat under load.
Alternatively bridge rectifier components are available. These bridge rectifiers consist of the four diodes required to make the bridge rectifier in a single encapsulation. The four connections are brought out and marked "+", "-" and "~". The "~" connection is used to connect to the alternating input. The + and - connections are obvious.
Some of these bridge rectifiers are intended for mounting on a printed circuit board and mat have wires for through hole mounting. Others may be surface mount devices.
Some bridge rectifiers are contained in larger encapsulations and are intended for mounting on a heat sink. As these rectifiers can dissipate significant levels of heat when high current levels are drawn, the heat sink capability is useful.
Bridge rectifier circuit design considerations
There are several points that need to be considered when using a bridge rectifier to provide a DC output from an AC input:
- Voltage drops: It must not be forgotten that the current flowing in a bridge rectifier will pass through two diodes. As a result the output voltage will have been dropped by this amount. As most bridge rectifiers use silicon diodes, this drop will be a minimum of 1.2 volts and will increase as the current increases. Accordingly the maximum voltage output that can be achieved is a minimum of 1.2 volts down on the peak voltage of the AC input.
- Calculate heat dissipated in the rectifier: The diodes will drop the voltage by a minimum of 1.2 volts (assuming a standard silicon diode) which will rise as the current increases. This voltage drop and the current passing through the rectifier will give rise to heat which will need to be dissipated. In some instances this can be easily dissipated by air cooling, but in other instances, the bridge rectifier may need to be bolted to a heat sink. Many bridge rectifiers are constructed to be bolted onto a heat sink for this purpose.
Bridge rectifiers are an ideal way of providing a rectified output from an alternating input. The bridge rectifier provides a full wave rectified output which enables better performance to be achieved in many instances.
Split supply bridge rectifier circuit
For many circuits like operational amplifiers, split supplies may be needed. It is possible to create a split supply for these and other applications very easily using a full wave bridge rectifier. Although it returns to the use of a split transformer, i.e. with a centre tap, it can be worth it to gain the combination of both negative and positive supplies using the bridge rectifier.
The circuit operates effectively and efficiently because both halves of the input waveform are used in each section of the transformer secondary winding.
The dual supply bridge rectifier solution does require the use of a centre tapped transformer, but a second winding would often be required anyway to provide the dual supply.
The full wave rectifier circuit based around the bridge of diodes performs well and is used in most full wave rectifier applications. It uses both halves of the waveform in the transformer winding and as a result reduces heat losses for a given level of output current when compared to other solutions. Also this solution does not require a centre tapped transformer (except for the dual supply version) and as a result the costs are reduced.
More Circuits & Circuit Design:
Op Amp basics Op Amp circuits Power supply circuits Transistor design Transistor Darlington Transistor circuits FET circuits Circuit symbols
Return to Circuit Design menu . . .