Last Updated on October 22, 2023 by Kevin Chen
Image of diodes source Freepik
In the world of electronics, diodes are always compared to valves. They allow the flow of electric current in one direction and not the other. Diodes are semiconductor devices that are manufactured by combining two types of materials; N-type and P-type materials. The N-type has negative electron carriers while the P-type has positive or holes electron carriers.
Diodes have a wide range of applications in the world of electronics. As long as you will need to control the flow of current in a circuit, you will have to think about buying diodes. But the big question is, how do I choose the right diode for my circuit? We have the answers. Keep reading as we discuss things that you should look at when choosing diodes.
Operation of diode
The working principle of diodes is controlled by their current-voltage characteristics (V-I). When a voltage is applied to one end of the diode, it will trigger the electrons to flow from the anode to the cathode. This means that the diode will be operating in a forward bias mode. When the voltage is applied is not enough to trigger the movement of current, there will be zero activity at the junction of the diode. This way, we can say that the diode is reverse-biased.
When it comes to connecting a diode to an electric circuit, a diode with the highest positive potential is connected to the P material while the negative potential is connected to the N material. This way the diode will be forward biased. On the other hand, if the positive terminal of the circuit is connected to the N material with the negative side is connected to the P material the diode is said to be reverse biased.
The diagram below illustrates the connection of diodes in a circuit.
Image source Circuit basics
The first step of buying diodes entails identification. You need to know the diode by its electric symbol. The schematic symbol of a diode entails an arrow and a line that cuts across the tip of the diode.
The image below illustrates a diode symbol and the important parts of the diode
Image source Wikimedia Commons
As you can see from the image above, there are two terminals that allows you to connect the diode into an electric circuit.
In the diagram above, the P-type material is represented by the base of the arrow while the N-type is at the tip of the arrow.
However, diode manufacturers usually use different symbols to represent the two terminals of diodes. In most diodes, the colored bands represent the cathode while the other end will be the anode.
You can use the manufacturer’s manual to verify the identity and polarity of the diode.
Factors to consider when choosing diodes
Here are the key elements of diodes that you should look out for:
Type of the diode
The very first element that you should consider is the type of diode that you should use in your electric circuit. Once you choose the right type, it will be easier to break down all the other technical requirements for the diodes.
There are different types of diodes and each type is best suited for a specific application area or circuit requirement. These types include:
- General purpose diodes: These are simple semiconductor diodes designed to allow current to flow in one direction only. In these diodes, electrons flow from anode to cathode
- Light emitting diodes: These diodes are designed to emit light rays. They are commonly used for lighting purposes in various application areas.
- Photodiodes: These are special diodes that use the reverse current to alter the illumination. They change the optical rays into electrical signals which are converted into different messages.
- Shottky diodes: They are also known as hot-carrier diodes They are mainly used as current rectifiers whereby they correct the flow of electric current at high frequency.
Other types of diodes include varactor diode, tunnel diodes, rectifiers, pin diodes among others.
Once you choose your desired type of diode, then you can proceed to vet your selection using other parameters.
Current features and characteristics
Current is among the key power specifications of the diodes that you should consider. There are various specifications that are associated with current. Let’s look at each of these specifications and the impact that they have on the performance of the diode in an electric circuit.
- Rated current/maximum forward current/IF: This is the maximum current at which the diode will operate safely without getting damaged. Any current below the rated one means that the diode will not run. On the other hand, exceeding the rated current will cause overheating or even blow up the diode. Of
- Maximum surge current (IFSM): After installing the diode in a circuit and when it is in operation, there is a high chance that it will have to be subjected to occasional current surges. The rated maximum surge current refers to the maximum current instantaneous current that the diode will be able to handle at any given time, especially in case of a power surge.
- Reverse current Idrm: This is the maximum reverse current that will flow through the diode. This current is created due to the movement of minority carriers.
- Forward current: This is the current in the diode when connected to the circuit in a forward voltage mode.
- Reverse saturation leakage current (IR): This is the maximum current when the diode is connected to the reverse voltage. Usually, it is directly proportional to the operating temperature of the diode.
Voltage characteristics of the diode
When choosing a diode, you should also pay attention to its voltage specifications. These specs include the following:
- Rated voltage: This is the maximum voltage that will facilitate the smooth operation of the diode without overheating or damage. Just like for the case of current, you should not exceed the rated voltage of the diode. Assuming that you know the voltage of your circuit, you should be able to buy a diode with the matching rated voltage.
- Breakdown voltage (Vbr): This is the minimum voltage that will trigger the breakdown in the diode. A slight increase of the breakdown voltage will cause a sharp increase in the reverse current.
- Maximum reverse voltage (VR): When you connect the diode to the circuit in the reverse direction, that voltage will be the reverse voltage. It should not exceed the maximum reverse voltage s stated by the manufacturer.
Before you choose a diode or the circuit, you have to verify its switching speed. This is the time taken by the diode to allow the flow of electric signals after the change of the diode’s polarity from forward bias to reverse bias. Usually, the higher the switching speed the better for you. But, again, it will all depend on the requirements of the circuit. The switching speed should match with other specifications of the circuit. For instance, it should not overwhelm the flow of electric current in a circuit.
Also, the switching speed usually matches the frequency of the circuit. A 4-nanosecond switching speed matches with the diode frequency of 125 megahertz.
Reliability of the diode
What does the reliability of a diode entail? It covers such as performance and durability of the diode. The electronic component should be able to deliver the best performance while at the same time serve its purpose on the circuit for long.
One way of verifying the reliability of a diode is to examine its physical and mechanical attributes. The diode should feature a solid design and construction. These two attributes show that it is built to last, especially if has been built of high-quality semiconductor materials.
Other than the performance features and parameters, you need to know whether the diode that you want to use in a circuit is safe for the environment. This is where the relevance of ROHS compliance comes in
ROHS stands for the Restriction of Hazardous Substances. It is a global policy that controls and monitors the use of hazardous substances in electronic components. This compliance is vital as it ensures that the diodes will not have negative impacts to the users and even the environment in general.
Common hazardous substances that are listed in the ROHS include lead, mercury, and chromium. Before you choose a diode, take your time to verify whether it is ROHS-compliant. You can even contact the diode manufacturer directly to verify this vital information about the compliance.
From this guide, it is clear that choosing a diode is a critical part of your project building. The diode should be perfect for the electric circuits that you are building. A good choice will guarantee a successful project. After all, your goal w= should be to connect the diode and allow it to perform its designated tasks on the circuit.
Once you are sure of the type, design, and specification of the diode, you can focus on other aspects of the circuit so that at the end of the day you have a running project.
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