In the world of electronics, the diode is one of the most essential and frequently used components. Whether you're working on a power supply, charger, LED lighting system, automotive stereo, or even a battery management system (BMS), chances are you're dealing with diodes. It’s critical to know that the diode is working properly before integrating it into your circuit—and that’s where a multimeter comes in.
So, if you’ve ever asked, “how to check diode on multimeter?”—you’re in the right place. In this comprehensive guide, we’ll walk you through everything you need to know about checking, testing, and interpreting diode behavior using a standard digital multimeter. We’ll also explore what makes a good diode, how different types behave during testing, and how companies like Jiangsu Donghai Semiconductor are contributing with high-performance diode products ranging from 30A 600V FRD to 30A 100V SBD for modern applications like OBC, lighting, charger, and inverter systems.
What Is a Diode?
Before we get hands-on, it’s important to understand what a diode actually is. A diode is a two-terminal semiconductor device that allows current to flow in only one direction. It’s a key component in rectification, voltage regulation, reverse polarity protection, and signal demodulation.
Diodes come in many forms: from Schottky Barrier Diodes (SBD) to Fast Recovery Diodes (FRD), Zener diodes, and even laser diodes. Each type has a unique electrical characteristic, but all diodes share the same basic principle—unidirectional current flow.
Why Is Diode Testing Important?
Testing a diode is vital for several reasons:
Ensures reliability before placing it into a circuit.
Identifies damaged or short-circuited diodes.
Diagnoses faults in chargers, inverters, BMS, and lighting systems.
Helps verify orientation and polarity in complex PCBs.
Faulty diodes can lead to power loss, overheating, or complete system failure—especially in high-stakes applications such as on-board chargers (OBC) or EV battery management systems.
How to Check Diode with Multimeter: Step-by-Step
The most accurate and efficient way to verify a diode’s functionality is by using a multimeter with diode tester mode. Here’s a simple walkthrough on how to test diode in multimeter:
Step 1: Set the Multimeter to Diode Mode
Most digital multimeters have a dedicated diode symbol (a triangle with a line) on the dial. Select this mode. If your multimeter doesn’t have a diode mode, use the resistance (ohm) mode as an alternative—but diode mode is preferred for accuracy.
Step 2: Identify the Diode Terminals
A standard diode has two ends:
Step 3: Connect the Probes
The multimeter should display a voltage drop between 0.2V and 0.7V for silicon diodes (lower for Schottky diodes like 20A 100V SBD or 30A 100V SBD).
If you reverse the probes, the meter should show “OL” (open loop), indicating no current flow—confirming that the diode is not shorted and is properly blocking reverse current.
Step 4: Interpret the Results
| Multimeter Reading | Diode Condition |
| 0.2V – 0.7V (forward) | Good |
| OL (reverse) | Good |
| 0V (both directions) | Shorted Diode |
| OL (both directions) | Open/Blown Diode |
This is the most reliable method for checking a diode with a multimeter.
Can You Check Diode Using Multimeter in Resistance Mode?
Yes, but it's less accurate. Resistance mode sends a lower voltage through the diode, which may not be sufficient to forward-bias it. Still, if your multimeter lacks a diode check multimeter mode, this is a decent alternative.
This method is commonly used in field testing, especially by engineers working on charger and lighting circuits in the automotive and telecom industries.
Testing a Diode in Circuit vs. Out of Circuit
For the most accurate results, always test the diode out of the circuit. Other components connected in parallel can interfere with the reading, leading to false positives or negatives.
However, in urgent cases—like diagnosing a BMS fault or an issue with an inverter—you can perform a quick in-circuit test by isolating one end of the diode or comparing against known-good components.
Exploring High-Performance Diodes from Donghai Semiconductor
Jiangsu Donghai Semiconductor Co., Ltd. is a trusted name in power semiconductor devices, known for its quality diodes designed for high-performance electronics.
Their product range includes:
| Product | Type | Voltage | Current | Applications |
| 30A 600V FRD | Fast Recovery Diode | 600V | 30A | Inverter, OBC, LED Drivers |
| 60A 600V FRD | Fast Recovery Diode | 600V | 60A | BMS, High-Current Chargers |
| 20A 100V SBD | Schottky Diode | 100V | 20A | Lighting, DC-DC Converters |
| 20A 200V SBD | Schottky Diode | 200V | 20A | Power Adapters, Telecom |
| 30A 100V SBD | Schottky Diode | 100V | 30A | USB-C Chargers, EV Supply |
These diodes are used in everything from fast-charging mobile devices to industrial-grade inverter systems. Their low forward voltage, high current capacity, and fast recovery times make them ideal for energy-efficient designs.
Applications Where Diode Testing is Critical
Chargers
In fast-charging systems, diodes control the current flow and prevent reverse current from damaging the circuit. A failed diode can lead to overheating or slow charging.
Lighting
In diode lighting, especially LED drivers, Schottky diodes are used for rectification and voltage clamping. Incorrect diode operation can cause flickering or total LED failure.
OBC (On-Board Chargers)
High-voltage FRDs like 30A 600V FRD are vital for managing AC-DC conversion in electric vehicle chargers. Faulty diodes can compromise charging efficiency and safety.
BMS (Battery Management Systems)
In BMS, diodes prevent battery discharge through parasitic paths and ensure safe charge routing. Regular testing diode behavior helps maintain battery life and system stability.
Inverters
In inverter systems, diodes control switching paths, manage power flow, and protect against voltage spikes. Fast recovery characteristics are essential for high-frequency operation.
Specialized Diode Use Cases and Testing Tips
Isolating Diode Car Stereo
An isolating diode car stereo is used to prevent back-feed of current between multiple power sources, such as ignition and battery. Testing these diodes ensures that your stereo remains operational without draining the battery.
12 Volt Diode
A 12 volt diode is typically used in automotive circuits to protect against reverse polarity. These can be tested the same way using a check diode multimeter mode.
Unidirectional Network Data Diode
A unidirectional network data diode is a cybersecurity device that allows data to flow only in one direction. While not a traditional electrical diode, the concept is based on unidirectional flow—similar to diode principles.
Can You Use a Diode with an Ohm Meter?
Yes, you can. However, as mentioned earlier, using an ohm meter may not provide precise readings. It’s more effective to use a multimeter with diode tester mode to get accurate forward voltage drop values.
On a Diode Laser, Which Way Y Axis Goes?
In diode lasers, the Y-axis typically represents beam direction or optical output. While this doesn’t impact testing a diode with a multimeter, understanding diode lasers is critical in medical, industrial, and scientific applications.
Diode Database: Why It Matters
A diode database refers to a catalog or documentation that includes specs like forward voltage, reverse current, recovery time, and power ratings. Having access to a reliable diode database helps engineers select the right component for their design and understand what readings to expect during testing.
FAQs
A1: How to check diode on multimeter?
Q1: Set your multimeter to diode mode, connect the red probe to the anode and black to the cathode. A good diode shows a forward voltage drop (typically 0.2V–0.7V) and blocks reverse current.
A2: What is the best way to test diode in multimeter?
Q2: Use the dedicated diode test mode. It sends a small voltage to forward bias the diode and measures the voltage drop, giving a reliable indication of diode health.
A3: Can you use a diode with an ohm meter?
Q3: Yes, but it’s less accurate. Ohm meters may not apply enough voltage to forward-bias the diode, leading to unreliable results.
A4: What is a 30A 600V FRD used for?
Q4: The 30A 600V FRD is a fast recovery diode ideal for high-frequency switching applications such as inverters, OBC, and industrial lighting.
A5: How does a 20A 100V SBD perform in chargers?
Q5: The 20A 100V SBD offers low forward voltage and fast switching, making it perfect for compact, energy-efficient chargers and power adapters.
A6: What’s the role of a diode in a BMS?
Q6: It ensures unidirectional current flow, preventing backflow that can damage batteries or other sensitive components in the system.
A7: How do I know if a diode is bad?
Q7: A failed diode will either show a short (0V in both directions) or open (OL in both directions) when tested with a multimeter in diode mode.
A8: What is a diode check multimeter mode?
Q8: It’s a function on digital multimeters that tests the forward voltage drop of the diode, offering a clear indication of its condition.
Knowing how to check diode on multimeter is an essential skill for every engineer, technician, and electronics enthusiast. Whether you're troubleshooting a smartphone charger, verifying an automotive stereo, or designing an industrial inverter, accurate diode testing ensures your circuit will perform reliably and efficiently.
With robust diode options like the 60A 600V FRD, 20A 100V SBD, and 30A 100V SBD, Jiangsu Donghai Semiconductor continues to lead the way in power device innovation—offering industry-grade solutions for BMS, OBC, lighting, and charger applications.
