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Automobile Diode – Importance in Automotive Reliability and Safety

An automobile diode is an electronic component that allows current to flow while protecting the electrical system from current spikes. Therefore, when they fail, your vehicle may experience a battery discharging faster and having excessive drain. 

Unfortunately, when addressing power-related problems, most car owners often concentrate on the battery. In such a situation, they overlook the entire electrical system, including the diode. 

In today’s article, we will discuss the importance of automotive diodes, their applications, types, and more. 

Why is there a need for a diode?

Automobile diodes stop outgoing current spikes from reaching the vehicle’s system and causing damage. Its functionality follows a regulation policy ensuring potential dangers in modern autos are less. Therefore, suppliers and manufacturers have found a way of including diodes in the system to match the standards of an excellent automobile. 

Consequently, you’ll be sparing yourself the heartache of electrical noise and improperly charging battery. 

Where is the location of a typical diode in a vehicle?

Check the alternator if you want to find the diode in your car, the diode is often beside it. The diodes are approximately six and convert AC from the alternator to DC, which goes to the battery and the entire car system. Moreover, they have stripped cylindrical shapes suitable for the unidirectional flow of current. 

An old rectifier in an automotive

(An old rectifier in an automotive)

Types of automobile diode

There are four main types of automobile diode. 

Automotive bridge rectifier diodes

This first diode is ideal for automotive battery charges and can operate at junction temperatures ranging from -40 to +175℃. It’s also used in heavy-duty applications like renewable energy converters, where AC voltage is converted to DC voltage.  

A bridge rectifier diode

(A bridge rectifier diode)

Currently, there are unbiased and biased diodes. An unbiased diode has no voltage supply. 

Automotive Schottky diodes

Secondly, we have a Schottky diode which is suitable for DC-DC converters. They serve automotive operations like phase shift circuits, forward active clamp, LLC, OBC, radio frequency, and Low Voltage DC-DC. 

They also have a semiconductor-metal junction temperature of -40 up to +175℃. 

Schottky diodes and rectifiers on a PCB

(Schottky diodes and rectifiers on a PCB)

Schottky diodes often experience small voltage drops at their terminals when you run current through them. Ideally, a low voltage drop means a high switching speed and better system efficiency. 

Automotive silicon carbide diodes

Undeniably, current electric and hybrid vehicles demand long batteries and electrical efficiency, making a silicon carbide diode the best option. 

It suits applications like motor drives, onboard battery charges (OBCs), and power factor correction circuits (PFCs), guaranteeing robustness and high-surge capability. Moreover, it comes in TO-247, DO-247, and TO-220AC packages. All of them have a PPAP capability and AEC-Q101 qualification. 

Signal diodes

They detect signals, making them suitable for a basic diode switch. Their common characteristics are medium-high forward voltage and low maximum current rating. 

Automotive ultrafast diodes

Lastly, we have ultrafast diodes operating in onboard chargers and DC-DC converters. As the name suggests, their specific designation is for high-speed applications and their soft recovery features. 

Further, they function at a temperature of -40 up to +175℃ and are relatively larger than other rectifying diodes. 

Ultrafast soft recovery diodes on a cooler

(Ultrafast soft recovery diodes on a cooler)

How to test the quality of the diode 

Diode test with a multimeter

(Diode test with a multimeter) 

Generally, we use a multimeter to test how well a diode performs. But before we begin our testing process, ensure you turn off the RX1K gear of the multimeter. The gear can produce an excess current that can damage the diode.

The two tests include: 

Reverse characteristic test

Simply connect the negative pole of the diode to the black test lead and then the positive pole to the red test lead. If the diode is in good condition, the values should be near or at an infinite value. 

Positive characteristic test

Put the multimeter’s red pen on the diode’s negative pole and the black pen on the diode’s positive pole. We aim to get a smaller forward resistance since it indicates a properly working diode. 

If your multimeter reads zero as the forward resistance, it indicates a damaged and short-circuited diode’s die. If it’s an infinite value, you’re dealing with a broken die. 

Note: Never use open- or short-circuited cables. 

Sometimes when you want to save money, ensure you buy diodes from companies that incorporate diode tests in their services. 

Application of diodes in automotive alternator

We will likely find diodes in several electrical devices in our daily lives. Some include radios, TVs, inductive loads (where they act as relays), signal modulators and demodulators, voltage regulators, signal limiters, diode lasers, photodiodes, switches, and signal mixers.  

In automotive alternative rectifiers, the diodes are useful for rectification. The diode will convert AC (Alternating current) to DC (Direct current). 

Principle of working

Normally, four diodes form a fully functional bridge rectification circuit during a single-phase alternating current. Here, the circuit will only reverse the AC’s negative half cycle. Therefore, the DC will be dynamic. 

Transforming AC power to DC power with a diode bridge and capacitor

(Transforming AC power to DC power with a diode bridge and capacitor) 

Nowadays, a car generator utilizes a three-phase AC instead of one. As such, the internal diode rectifier will need a minimum of six diodes to convert the AC to DC. 


To conclude, we hope you are now clear on how diodes work, their location in the car, and various types. Remember also to check our website for your wiring harness needs. We’ll be more than happy to help.

I am Lillian Yang, having been a sales manager for over 10 years.

I have received many positive reviews from customers. They have praised our excellent service, on-time delivery, and high-quality cable assemblies.

For your projects, please provide cable assembly files/images/smples, etc., so that I can send you a quotation within 24 hours.

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