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How Does a Diode Do Transient Voltage Suppression?

Author: Apogeeweb Date: 18 Jan 2021  215

transient voltage supression

Introduction

In electronics, transient voltage suppressor (TVS) diodes are components that protect sensitive circuitry from being damaged due to high voltage transients. Because tvs diodes are constructed with large cross sectional area junctions for absorbing high transient currents. The primary source of high voltage transients are electrostatic discharge, electrical fast transient, and surge events. This notes will tell you how does a tvs diode work to prevent a circuit malfunction and protect devices.

Catalog

Introduction

Ⅰ Transient Voltage Suppressors (TVS)

1.1 What Does a TVS Diode Do?

1.2 What Are Transients Supposed to Be?

1.3 What Causes a Circuit to Be Transient?

1.4 Transient Voltage Suppressor Types

Ⅱ Transient Voltage Suppression Diode

2.1 TVS Diode Overview

2.2 TVS Diode Types

Ⅲ How Do You Use TVS Diode for Circuit Protection

3.1 TVS Diode in Circuits

3.2 Major TVS Diode Parameters

Ⅳ Conclusion


Ⅰ Transient Voltage Suppressors (TVS)

1.1 What Does a TVS Diode Do?

Transient voltage suppressors or TVS are devices of protection used to save the circuits from this unexpected voltage or current spike. Positioning these TVS devices in parallel with the circuit is the primary way to protect a circuit from overvoltage.

1.2 What Are Transients Supposed to Be?

Transients are spikes of short duration in voltage or current that can in several ways damage a circuit. Some transients only occur once, and some of them may be repetitive. These transients vary from a few millivolts to thousands of volts and can last for hundreds of milliseconds to nanoseconds.

1.3 What Causes a Circuit to Be Transient?

Transients may be triggered by links in a circuit that are internal or external. For example, due to inductive load switching or defective contacts in switches and connectors, transients may be produced internally. It can be produced externally because of lightning strikes or inductive switching.

1.4 Transient Voltage Suppressor Types

Metal oxide varistor, TVS diode, Zener diode or bypass capacitor are several types of TVS devices that can be used for transient voltage suppression.
Transient Voltage Suppressors can be divided into two types, clamping and crowbar, based on service. Clamping devices restrict the voltage to a level which is fixed. They consume the excess energy of the overvoltage event in doing so. An instance of clamping devices is TVS diodes.
On the other hand, once activated, Crowbar devices effectively shorten the protected line, redirecting the excess energy away from the protected circuit. As you can see in the graph below, when a trigger voltage (spike) is detected, the crowbar device shorts the circuits such that the line voltage is decreased, then the line voltage rises again to a stable state for regular circuit operation after some time as the crowbar device delays the circuit.

transient voltage suppression diode symbol

Transient Voltage Suppression Diode Symbol

Ⅱ Transient Voltage Suppression Diode

2.1 TVS Diode Overview

The transient voltage suppression diode ((ESD protection diode)) is a solid-state PN-Junction diode explicitly designed to remove the sudden or momentary effects of overvoltage on sensitive semiconductors and circuits. TVS diode is a clamping system, so it absorbs the excess energy of the overvoltage event if the induced voltage reaches the avalanche breakdown voltage, and then automatically resets after overvoltage situation. Although it is true that standard diodes and Zener diodes can also be used for overvoltage/transient safety, since standard and Zener diodes are designed for rectification and voltage control, they are not as robust as transient voltage suppressor diodes.

2.2 TVS Diode Types

It is possible to classify Transient Voltage Suppressor Diodes into two groups. One of them is unidirectional, and the other is bidirectional.
Like every other avalanche diode, a unidirectional transient voltage suppressor diode acts in the forward direction as a rectifier in a circuit, and this unidirectional diode is made to withstand very high peak currents. The unidirectional TVS diode symbol is seen in the picture below, and it's almost like a Zener diode.
On the other hand, two mutually opposing avalanche diodes connected in series with each other can represent a bidirectional transient-voltage-suppression diode. In parallel with the system or circuit to be secured, these diodes are connected. These diodes are produced as a single element, unlike the symbol. The Bidirectional TVS Diode symbol is shown in the picture below.

Introduction to Transient Voltage Suppressors (TVS) Characteristic

Introduction to Transient Voltage Suppressors (TVS) Characteristic

Ⅲ How Do You Use TVS Diode for Circuit Protection

3.1 TVS Diode in Circuits

In parallel with the system or circuit to be secured, TVS diodes are attached. The TVS system is specifically designed to break down at a particular voltage level and, without sustaining damage, conduct large quantities of current.
The TVS diode appears as an open circuit under normal voltage conditions, but a low leakage current is present. The TVS diode junction avalanches when the usual voltage reaches a certain amount and overvoltage is redirected from the safe circuit as a result and shunted through the TVS diode. When the overvoltage goes down, the system automatically resets.
In addition, the VI characteristic curve of the tvs diode is similar to that of a Zener diode, TVS diodes are specifically designed, characterized, and tested for transient voltage suppression. By contrast, zener diodes are designed and specified for voltage regulation.

3.2 Major TVS Diode Parameters

Many types of TVS diodes, equipped for a particular application, are on the market. When selecting a TVS diode to protect an external interface, there are a couple of key parameters you want to pay special attention to. Here is the following parameters in the datasheet to help you find a right TVS diode.

  • Reverse Stand-Off Voltage (VR)
    The highest voltage that can be applied to the protector without the system actually being triggered is the reverse stand-off voltage. The VR of the system should be equal to, or greater than, the peak operating voltage of the safe circuit. This is to ensure that the regular circuit operation or signal voltage is not clipped by the safety system.
  • Breakdown voltage (VBR)
    The voltage at which the diode can begin to protect and conduct current is the breakdown voltage. The VBR is usually defined at 1mA.
  • Clamping Voltage (VC)
    The clamping voltage is the maximum voltage that will be exposed to the safe circuit during the event of the test waveform. The clamping voltage for a 1A or 2A waveform that has an 8μS rise time is given on most datasheets.
  • Peak Pulse Current (IPP)
    The highest current which the safety system can withstand is the peak pulse current.

transient voltage suppressor diode

Ⅳ Conclusion

The TVS diode is commonly used in low-energy circuits and systems for diversion/clamping, and in circuits for ESD safety. Because one advantage of using external TVS diodes is that they typically provide level four IEC ESD protection. Under normal operating conditions, the TVS diode presents a high impedance to the protected circuit. Ideally, the device appears as an open circuit, although a small amout of leakage current is present. TVS diode applications can be found in data and signal lines, memory for microprocessors and MOS, power lines for AC/DC, and telecommunication equipment.

 

Frequently Asked Questions about TVS Diodes

1. What is Transient Voltage?
A transient voltage is a temporary unwanted voltage in an electrical circuit that range from a few volts to several thousand volts and last micro seconds up to a few milliseconds. ...Faulty contactors and lightning are the most common source of transients.

 

2. How does a transient voltage suppressor diode work?
Transient Voltage Suppressor Diode is a clamping device, so whenever the induced voltage exceeds the avalanche breakdown voltage, it absorbs the excess energy of the overvoltage event, and then it automatically resets after overvoltage condition.

 

3. Which device can be used as a transient suppressor?
transient voltage suppression diode
One such common device used for this purpose is known as the transient voltage suppression diode that is simply a Zener diode designed to protect electronics device against overvoltages.

 

5. What does a suppression diode do?
A transient-voltage-suppression (TVS) diode, also transil or thyrector, is an electronic component used to protect electronics from voltage spikes induced on connected wires.

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