A diode bridge is an array of four diodes that rectifies AC power to produce a stable DC output. Diodes allow current to flow in one direction, breaking one half of the AC cycle. Capacitors can smooth out the remaining AC ripple. Diode bridges are used in various applications, from small power supplies to large industrial ones, and remain the cheapest and most convenient method for producing DC power from AC supplies.
A diode bridge is an array of four diodes interconnected such that an alternating current (AC) supply applied to two of the four points on the bridge will produce a direct current (DC) output at the remaining two. A diode bridge is therefore an electrical component for smoothing or rectifying an AC power supply to produce a DC output. A great example of this assembly at work is an AC cell phone charger which, when plugged into an AC outlet, supplies a DC current to charge the phone.
To understand how a diode bridge works, you need to know the basic differences between AC and DC power and how diodes work. Most people are familiar with the use of batteries in household appliances, toys, cameras and telephones. A battery is a good example of a DC power supply that has set polarity, meaning a set positive and negative terminal that never changes. The AC adapter in a household power outlet has alternating polarity that reverses approximately 50 to 60 times per second.
When an AC power supply is used to drive DC equipment, this alternating or reversed AC polarity must be smoothed out or rectified to produce the stable, unchanging polarity that characterizes a DC power supply. Without this rectification, AC power will damage or destroy the unit. In most applications, this smoothing is achieved using a bridge rectifier or diode bridge.
Diodes are electronic components that allow electric current to flow in only one direction. When four diodes are interconnected in a rectifying configuration, they will effectively break one half of the AC power alternating cycle and let one half pass through the bridge. The power that can pass through the diode bridge is not a particularly smooth DC current, but at least it exhibits a stable polarity or positive-negative relationship. This is known as half-wave rectification as half of the AC cycle wave is removed or blocked. To smooth out the remaining AC ripple from the supply, capacitors can be placed between the positive and negative outputs.
Diode bridges are used to produce DC power in a number of different applications ranging from small power supplies on electronic boards to massive industrial examples capable of powering large electromagnets and DC motors. The physical size of the assembly is all that changes in these applications; the basic construction of the bridge remains the same. While there are other ways to produce DC power from AC supplies, the diode bridge remains the cheapest and most convenient method.
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