How to Check a Bridge Rectifier

An unrectified AC signal switches polarity between positive and negative values.

Most electronic equipment requires a direct current (DC) input, meaning that the alternating current (AC) power from the wall must be rectified before it can be used. A bridge rectifier, or full-wave rectifier, is a simple circuit made up of four diodes. Its output maintains the same polarity, regardless of the polarity of the input voltage. To check that a bridge rectifier is working properly, it must be verified that the polarity of the output does not change when the polarity of the input is reversed.

Things You'll Need

• Voltage source (such as battery, transformer or function generator)
• Oscilloscope or multimeter

Instructions

Using a Battery

1. Connect battery to input leads of bridge rectifier circuit.

2. Measure the output voltage of the circuit using a multimeter or oscilloscope.

3. Reverse the battery. If the output is unchanged and nonzero, the circuit is working.

Using an Oscillating Voltage Source

1. Connect the oscillating voltage source (transformer or function generator) to the input leads of the circuit.

2. Using a multimeter, measure the output voltage. For a sinusoidal input signal, it should read roughly 0.6 of the amplitude of the input, the average value of the rectified sine curve.

3. If using a transformer, you can observe the rectified waveform on an oscilloscope. Connect the oscilloscope to the output leads of the rectifier. The rectified waveform should look like the absolute value of a sine curve, or a series of "hills."

Tips & Warnings

• Diodes are easy to blow. Placing a resistor in series with the voltage source will reduce the risk of accidentally overloading a diode.

• Beware of unintentional grounding issues if you are using an oscilloscope with a function generator, both which are referenced to the same ground. To avoid these possible problems, use a transformer as your alternating voltage source (which is not referenced to ground) or a differential amplifier with your oscilloscope.

References

• "The Art of Electronics"; Paul Horowitz and Winfield Hill; 1989