How to Test a Diode

How to Test a Diode

A diode must be tested to assure its dependability in electronic circuits. Diodes are semiconductor devices that allow one-way current flow but limit the other. Diodes are essential in rectifiers, voltage regulators, and signal processing circuits because to this property. Technicians and engineers can test diodes for operation and flaws. This tutorial will explain the purpose and relevance of diode testing, explore the numerous types of tests, describe the testing equipment, and provide a step-by-step approach.

Diode Testing Goal

A diode is tested to ensure correct operation and compliance with specifications. Technicians and engineers can test a diode to see if it allows forward current flow and blocks reverse current. Testing can also detect damaged diodes that affect electronic circuit performance. Diode testing ensures circuit diodes work properly, reducing the risk of failure.

Diode Testing Matters

To maintain electrical circuit reliability and efficiency, diode testing is crucial. Diodes need to rectify alternating current, regulate voltage, and protect sensitive circuit components from reverse voltage. A diode that malfunctions can impede current flow or harm a circuit. Diodes can be properly tested to identify any flaws early and fix or replace them. A thorough testing method improves electrical equipment quality and durability and prevents costly repairs or risks.

Checking a diode’s functionality. The good news is that diode testing requires no fancy equipment. A basic multimeter suffices. Use an analog or digital multimeter? Analog and digital multimeters are common. The needle display of analog multimeters has been around for decades, while digital multimeters use LCD screens. Both can test diodes, but digital multimeters are easier to read. This post will show you how to test diodes with each multimeter to determine your preference. However, a few simple steps will reveal if your diode is working or needs to be replaced. Let’s begin!

Introduction to Diodes: What Are They?

Diodes are two-terminal electrical components that allow one-way current flow. As an electrical valve. Many electronic devices control current flow via diodes.You must understand diode basics to understand how they work. Simple diodes consist of two semiconductors: an N-type with extra electrons and a P-type with extra holes for electrons. Electrons and holes recombine and current flows when the diode is forward biased from P to N.Current cannot pass through a reverse biased diode because electrons and holes are driven apart. The diode effect allows one-way current flow.

Some common diodes are:

  • Rectifier diodes block one flow direction to convert AC to DC electricity.
  • Zener diodes regulate voltage by restricting flow until a reverse bias threshold is met.
  • LEDs emit light as current passes through them.
  • Schottky diodes lose less power as heat due to their reduced forward voltage drop. Common in power supply.
  • Photodiodes generate current when lit. Used in light-detecting circuits.
  • Diodes are essential to many electronic circuits. Learning how diodes function and their fundamental properties can help you test and troubleshoot them.

Diode Testing using Analog Multimeter

Diode testing with an analog multimeter is simple. Analog multimeters employ needles to display scale readings, unlike DMMs. Basic diode testing is easy with analog multimeters, even though DMMs are more precise.Analog multimeters must be set to the Rx1 or Rx10 scale to measure low resistances to test diodes. Start with the more sensitive Rx1 scale.

Connect diode test leads.

Attach the red test lead to the diode’s positive anode terminal and the black lead to its negative cathode. Longer anode leads and striped cathodes are typical.

Remember the meter reading

A working diode should have some resistance in one direction and significantly larger resistance in the other. For small signal diodes, the needle moves and stabilizes to indicate forward resistance, which is usually 100 ohms or less.

Reversing the leads, record the reading again.

High reverse resistance means the needle scarcely moves when you reverse the leads. A shorted or open diode has readings that are similar or very low in both directions.

Interpret results

If the diode tests as specified, it works. The diode may be short, open, or leaking and should be changed. Analog meters are suitable for basic good/bad diode testing but not resistance measurements.Analog multimeters are useful for diode and continuity checks, even if digital ones are more accurate. Quickly master diode testing with some practice.

Diode Testing with a Digital Multimeter

Set a digital multimeter (DMM) to diode test or continuity mode to test a diode. This lets the multimeter transmit a little current through the diode to test its conductivity.

  • Testing Diode
  • Find the DMM diode test setting. Usually a diode sign with an arrow pointing at a line. Set your meter’s auto-ranging.
  • The red probe should go to the diode’s anode and the black probe to its cathode.
  • Record your meter reading. A good diode reads 0.5–0.8 volts. Diodes may fail if the reading is lower or higher.
  • Connect probes to diode leads in reverse. The diode is blocking current flow in that direction if the readout is ‘OL’ or infinity. If you get voltage again, the diode is bad.
  • Compare results from similar diodes. Diodes usually vary 0.1 to 0.2 volts. Larger deviations may be problematic.
  • Any diode that fails these tests should be replaced. Faulty diodes can damage circuit components or impede operation.

Make sure to attach DMM probes to diode leads according to polarity while testing them. Reversed connections can damage the diode or meter. Using a DMM to examine diodes can be quick and easy with practice, helping you troubleshoot and verify devices.


Now you know how to test diodes with analog and digital multimeters. Digital multimeters are safer and more accurate than analog ones, despite nostalgia. Their auto-ranging feature simplifies setup and prevents component damage. With diodes, the DMM’s auditory continuity test offers you confidence the part is working properly. Take your digital multimeter while troubleshooting a circuit or verifying new parts—your circuits will thank you!

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