How to Test a Bridge Rectifier with a Multimeter

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Have you heard of a bridge rectifier? In case you didn’t know, a bridge rectifier, also called a full bridge rectifier, is a set of four or more diodes in a bridge circuit configuration. It gives the same output polarity to either input polarity or is utilized for converting an AC input into a DC input. 

What is a Bridge Rectifier?

Rectifiers allow you to convert from AC to DC. For a quick recap, AC is currently switching between flowing forwards and backward at regular interviews while a DC current flows in a single route. They normally depend on a bridge rectifier. 

Every rectifier utilizes P-N junctions. These semiconductor devices enable electric current flow in a single course from the construction of P-type semiconductors together with n-type semiconductors. Moreover, the p-side has an excess hole, meaning it is positively charged. Meanwhile, the “n” side is negatively charged along with electrons in their outer shells. 

Most circuits with that technology are constructed with a bridge rectifier. You see, bridge rectifiers translate AC to DC with its system of diodes made of a semiconductor material in either:

  • a full-wave method rectifying both directions of the input OC 
  • a half-wave method rectifying one direction of the AC signal 

Remember that semiconductors are materials allowing current flow as they are made of metals such as metalloids or gallium-like silicon, which are contaminated with materials such as phosphorus as a way of regulating current. You can utilize a bridge rectifier for various purposes for a broad spectrum of currents.

It’s worth mentioning that bridge rectifiers benefit from outputting more power and voltage than other rectifiers out there. Regardless of those advantages, bridge rectifiers experience the necessity to use four diodes with additional diodes than other rectifiers. That causes a voltage drop that lowers the output voltage. 

How Does a Bridge Rectifier Work?

Bridge rectifiers utilize four diodes organized smartly to transfer the AC supply voltage to a DC supply voltage. The output signal of that circuit is always of the same polarity irrespective of the input AC signal’s polarities. 

The AC signal is applied at the input terminals a and b, and the output is observed across load resistor R1. 

This is how a rectifier circuit responds to an AC signal along with changing batteries at each cycle. 

  1. The diodes D2 and D3 in the first positive half cycle of the AC signal become forward biased and begin conducting. The diodes D4 and D1 will be reverse biased and won’t conduct at the same time. 

The current then will flow throughout the load resistor through the two forward-biased diodes. The voltage perceived at the output will be negative at terminal C and positive at terminal D.

  1. The diodes D1 and D4 will be forward biased throughout the negative half cycle. Diodes D2 and D3 will then become reverse biased. Further, the positive voltage will show on the D4 anode, while the negative voltage will be applied to the D1 cathode.

Please take note that the current at this point will be flowing through the load resistor and will have a similar course as it has with the positive half cycle. Hence, whatever the input signal’s polarity, the output polarity will be the same. Also, the AC signal’s negative half-cycle has been inverted and is showing us a positive voltage at the output. 

What are the Common Uses of a Bridge Rectifier?

The major use of a bridge rectifier is to change an AC supply into DC power. Every electronic device needs a direct current. That’s why bridge rectifiers are utilized inside the power supplies of nearly all electronic devices.

Keep in mind that bridge rectifiers are utilized for locating the amplitude of modulated radio signals. That signal might be increased before it’s located. If it’s not, a diode-based with a fixed voltage or a low voltage drop diode should be utilized. 

Also, rectifiers are utilized to provide polarized voltage for welding purposes. Control of the output current is needed in those circuits, not to mention that it might be accomplished by changing some of the diodes in the bridge rectifier with thyristors. 

Thyristors are diodes where their voltage output could be controlled by switching off and on with phase-fired controllers. 

How Do You Test a Bridge Rectifier? 

  1. Prepare your multimeter (DMM) for the diode check. Insert the probes into the digital multimeter.
  1. Please turn on your digital multimeter and set it into a diode-tester function, as guided by the instructions for your certain model. 
  1. Test the AC inputs. Touch one probe leads to one of the AC inputs, and the other leads to the other input. The multimeter normally suggests an overload. That means there’s too much resistance to measure
  1. Swap the leads at the inputs and repeat the procedure. Any numerical reading suggests that a diode is leaking current in the reverse-biased course.
  1. Test your individual diodes. Put the positive lead to an AC input, and the negative probe lead to the positive output. See the reading. Swap the leads and check the reading on the meter display. Do the same process again for the other AC input.
  1. Take note that a successful check shows that one diode conducts within the forward-biased direction, shown on the meter as turn-on voltage of at least 0.7 volts. 
  1. Do the same process between the negative output and the AC inputs. Disconnect the leads and turn off the multimeter. 
  1. For the last step, check whether the bridge rectifier is usable or not. If every diode passes that check test, then it means your bridge rectifier is good to use. But even if one diode leaks, you should replace it right away. 

Final Thoughts

There’s no doubt that rectifiers convert AC to DC from numerous power supplies in power supply circuits. That’s practical as DC is normally delivered across long distances before converting to AC for electronic devices and electricity. Such technologies make good use of the bridge rectifier that can deal with the change in voltage. 

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