What Is a Full Wave Bridge Rectifier?
The power lines that bring us electricity carry A.C., or alternating current. A.C. is fine for motors, light bulbs, and heaters but many of the things we use, from fax machines to stereos to cordless shavers, need D.C., or direct current. The appliance's power supply does the job of converting A.C. to D.C. Some of these you can see, like the chunky black wall plugs that everything runs on these days; some of them you don't, if it's inside the equipment. All of them use a full-wave bridge rectifier. It is the active component that changes A.C. to D.C.
Other People Are Reading
-
Function
-
Most bridge rectifiers are made up of four identical diodes. Diodes are electronic devices that conduct current in one direction only. Two diodes conduct during the positive half of the A.C. waveform, giving a positive voltage output. The other two diodes conduct during the negative half, but in the opposite direction, so it again outputs a positive voltage. The diamond-shaped connection arrangement is what electronics engineers call a bridge.
Size
-
Bridge Rectifiers come in various sizes for different uses. A typical one used to power small home electronics is about the size of a dime, in a flat rectangular plastic package. Rectifiers for home stereos are bigger, up to matchbook size. Stereos use more power than cell phones or answering machines; more power means some parts get hotter and they need to be bigger and sturdier to take the heat. And as current and voltage requirements go up, connectors and other metal parts need to be larger and better-insulated.
-
Identification
-
Bridge rectifiers are usually small flat black plastic packages with four leads, two marked "A.C." or a "~" symbol, one marked with a negative (-) and one marked with a plus (+). The rectifier may be mounted on a metal heatsink. In other cases, the rectifier will be a set of four identical diodes arranged closely together in a row or a diamond pattern. In older or very high-power equipment, the rectifier may use vacuum tube diodes. These have four pins on the base and a metal cap on the top.
Polyphase Rectifiers
-
High-power and high-voltage applications can call for a polyphase rectifier. This takes advantage of the fact that A.C. power comes in three overlapping phases. Most household appliances use the single-phase current that comes at the wall outlet, but motors and equipment may be wired for two or three phase power. Polyphase rectifiers are very similar to regular ones; they use six diodes for three phases in place of the normal four. They output D.C. just as a simpler rectifier does.
Warning
-
The electricity running through bridge rectifiers in most home devices will be under 30 volts. However, the rectifier's connected to a transformer conducting 110 volts or more. Likewise, other circuits in the appliance may be carrying 110, and some components can hold high voltage even with the power off. 110 volt household current is hazardous and should be treated with caution.
-
