Last Updated on October 22, 2023 by Kevin Chen
Image source Freepik
Surge and ESD (electro-static discharge) have a common feature; both result in the generation of high voltage which has adverse effects on electronic devices and components. They can cause serious damage to the electric circuits. Sometimes, they can even trigger fire accidents that will damage properties. This usually happens when the surge and ESD cause voltage in the circuit to exceed certain dangerous limits.
Various surge protection and ESD protection devices have been specifically designed to guard against these two electric phenomena. These devices are embedded with many features and components that ensure they execute the protection function without any issues. One of the devices is the diode. In this article, we are going to discuss how diodes are used in surge protection and ESD protection.
Overview of surge protection
We can define surge protection as mechanisms that are designed to protect electronic devices from the effects of a voltage surge. Usually, a power surge will result in a sudden increase of the transient voltage in the electric circuit. This voltage will be way higher than that that is supplied to the circuit and is likely to find its way to various electronic components in the device.
Suppose the components are rated 5V yet the transient voltage due to the power surge is 20V, it is easy to predict what will happen. The components will blow up hence damaging the whole device. Electric circuits that make up the device will not have the capacity to handle the power surge.
There are various causes of power surges. They include faults in the main power supply, lightning, and other factors both inside and outside the electronic device.
The primary goal of surge protection is to minimize the negative impact of a power surge. One way of protection is by directing the excess current away from the electric circuits in the device. Diodes are quite good at this as they have the ability to determine the direction of the current flow in the circuits. Some surge protection devices work by absorbing the excess power from the circuit.
Overview of ESD protection
Just like surge protection, ESD protection is necessary on all electric devices. Electrostatic discharge is generated when two objects rub against each other. The objects must have electric potential and once they come in contact with each other, they will generate this energy. Just like in the case of a power surge, an instant effect of ESD is the introduction of excess voltage into the circuit. This extra power is likely to end up causing serious damage to various electronic components that make up the device.
One thing about ESD is it is difficult to predict its source. Sometimes a stream of air rubbing against the device can generate the charges. Also, whenever you are working on the device, you may end up generating electrostatic discharge.
ESD protection refers to various mechanisms that are designed to offer protection against the dangers of ESD. These protection measures include having a designated working zone, wearing of the ESD protection devices and even integrating ESD protection integrated circuits.
The use of diodes in surge and ESD protection devices
From the overviews of the ESD and surge protections, it is clear that both entail the generation of unwanted electric current. Once these charges have been generated, they will flow to a particular destination. The diodes are included in the protection measures because they allow current to flow in one direction only and not the other. By doing so, they will be able to shield or protect electronic components from the dangers that are associated with the excess current in a circuit. This way, the device will be fully protected from the effects of surge and ESD.
Zener diodes and varistor diodes are the two common types of diodes that are used on ESD and surge protection devices. The fact that they are diodes means that they allow the unidirectional flow of electric current.
Another unique feature of the Zener diodes is they have high resistance when the terminal voltage in the circuit is low. However, the resistance tends to be low when the voltage at the terminals gets high. With this working mechanism, it means that excess current will bypass the main terminal voltage hence sensitive components will be completely protected from the power surge.
Zener diode as anti-ESD and surge protector
Zener diodes are commonly mentioned when it comes to surge protection as well as ESD protection in electric devices and appliances. The working principle of a Zener diode is based on its ability to operate in the reverse-biased mode. Each Zener diode comes with a defined ‘Zener voltage’ and when the electric current in the circuit exceeds this voltage it will start conducting electric current in the opposite direction.
A single Zener diode will provide protection against ESD when connected on the negative terminal of the circuit. To enhance the effectiveness of this diode, two Zener diodes are used as they will provide high-voltage protection from both sides of the circuit.
In recent years, Zener diodes have replaced varistors when it comes to surge protection and as well as ESD protection applications. There are several advantages that come with using Zener diodes over the varistors.
The image below illustrates the connection of two Zener diodes in a circuit (source Panasonic)
Image source Panasonic
Why are Zener diodes replacing varistors in the surge protection and ESD protection?
One of the reasons for the popularity of Zener diodes is their compact size. Zener diodes are lighter than the varistor and hence are easy to handle and incorporate into the circuit. Other than weight, they are also smaller in size hence can fit in small spaces especially when you want to mount the diode onto a circuit board. Also, it will be easier to design an integrated circuit knowing that the Zener diode will take up a smaller space.
Another key advantage o the Zener diodes over varistors when used for ESD and surge protection is they offer better resistance to excess voltage. With better resistance, it means that more of the excess current and voltage will be trapped by the surge protection devices hence offering better protection than the varistor.
The versatility of the Zener diodes is another key reason behind their popularity. They can support both low-voltage and high-voltage applications. This also means that they are compatible with a wide range of electronic devices and circuits.
Transient-voltage suppression (TVS) diode
The role of diodes in surge protection and ESD protection comes out clearly through the transient-voltage-suppression (TVS) diodes. Also known as ESD protection diode, this is a special type of Zener diode. This means that its working principle is based on the operation of the Zener diode whereby the electric conduction is due to the reverse biasing of the diode. The Zener voltage of this ESD protection diode is maintained by a regulator and this voltage is used for absorbing the excess current due to ESD and power surge.
So, how do the ESD protection diodes work? Usually, the diodes are installed between the power lines and the ground of an electric circuit. This connection ensures that they can protect the main circuit. When everything in the circuit is normal, such that there is no power surge, little or no current will flow through ESD diodes. The little current that will find its way into this circuit will be due to the current leakage.
Each ESD that is connected in the circuit has a defined Zener voltage which cannot be broken down easily unless the current exceeds a particular threshold which is the breakdown voltage (Vbr).However, once the voltage surge exceeds the reverse breakdown voltage, the ESD diodes will direct the excess electric current the ground line, an effective way of managing the excess power.
Key features of TVS diodes
Here are some main features of transient-voltage-suppression diodes that make them suitable for the ESD and surge protection functions:
- Breakdown voltage: This is the voltage at which the diode will start conducting the electric current.
- Leakage current: This is the current that is conducted through the diode when the voltage applied to the circuit is below the maximum reverse standoff voltage.
- Energy capacity: This is the amount of energy that the diode can absorb before discharging to the ground.
- Parasitic capacitance: Given their function, TVS diodes can work as parasitic capacitance. They store the excess charges due to ESD and power surges. The lower the capacitance value the better.
Now you know everything about surge protection and as well as ESD protection. Diodes play important roles in the building and creation of these protective devices. If you are an electronic device manufacturer or you are a startup working on surge protection and ESD protection devices, you have no option but to get the right diodes for your project. The diodes should guarantee maximum protection against power surges and as well as electrostatic discharge.
When choosing diodes ensure that their power specifications match the requirements of the devices that you would like to protect from power surges and ESD. Consult experts in the electronic industry and at the same time ensure that you buy from reputable and reliable diode suppliers in China.
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