TVS Diode Symbol, Working, Applications & Types

TVS diode or Transient voltage suppression diode is also known as clamp diode, transil, or thyrector. The TVS Diode is an essential component in power electronics design circuits used for handling transient spikes.

In this article, we will cover the basics of the TVS diode such as working, symbol, VI characteristics, and how it is different from a Zener diode.

What is a TVS Diode?

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The TVS diode is a protection diode. They are designed to protect electronic circuits from transients and overvoltage threats such as EFT (electrically fast transients), ESD (electro-static discharge), inductive load switching, and even lightning strikes. They are silicon avalanche devices with fast response time, low capacitance, low leakage current, and low clamping voltage.

What is a TVS diode?
What is a TVS diode?

Note: TVS diode is often considered a type of Zener diode that utilizes TVS characteristics in the breakdown region. Though they both works in the breakdown region, their construction and application are totally different.

Transients, which are sudden spikes in voltage or current, can harm a circuit in different ways. These range from millivolts to thousands of volts and can occur from a few nanoseconds to hundreds of milliseconds. Transients occur due to internal and external connections in the circuit. Transients may occur once or repeat depending on the conditions.

TVS Diode Symbol

There are two types of TVS diode- Unidirectional and Bidirectional TVS diode. Their symbol is given below:

TVS diode symbol
TVS diode symbol

A) Unidirectional TVS Diode       B) Bidirectional TVS Diode

What is a Unidirectional TVS Diode?

A unidirectional TVS diode means it works as a normal rectifier diode when forward-biased. The only difference is that it is used specifically for overvoltage spikes protection in one direction(reverse-biased) and can handle very large peak currents.

That is why, in reverse-biased mode, it only acts as a clamping device for positive voltages.

VI Characteristics of Uni and bidirectional TVS diode
VI Characteristics of Uni and bidirectional TVS diode

What is a Bidirectional TVS Diode?

A bidirectional TVS diode consists of two unidirectional diodes connected in series and can operate in both-direction as per need. It has a symmetrical breakdown voltage in both forward and reversed biased directions and so it works as a clamping device for both positive and negative voltages.

How does a TVS diode work?

TVS diode in a circuit
TVS diode in a circuit

In the image above, the TVS diode is connected in parallel with the circuit under protection. It works on the principle of avalanche breakdown in reverse bias mode, suppressing all voltage spikes above its breakdown voltage.

There are two modes of operation of a TVS diode in a circuit.

Working of TVS diode
Working of a TVS diode

Normal operating mode: When there is no voltage spike, the TVS diode acts like a normal diode in reverse bias mode, as an open circuit with negligible leakage current.

Under normal conditions, a TVS diode acts as a capacitor with very small capacitance.

Overvoltage operating mode: When a transient spike occurs, the diode immediately goes into the breakdown region. In this region, it has a very low impedance, providing a short path for the high transient current. As a result, most of the transient current passes through the TVS diode, thus protecting the load.

Applications and uses of TVS diode:

TVS diodes are designed to protect electronic circuits from voltage spikes and transients. They are used in various applications such as:

  • Surge protection for power lines or communication lines, such as in telephones, modems, and LANs.
  • In automotive industries where TVS diodes are used to protect the car’s delicate sensitive electronic components from short circuits and overvoltage.
  • Electronic devices, such as mobile phones, TVs, etc., to protect their delicate components from voltage spikes.
  • Surrounding a transistor in an amplifier circuit to protect it from any possible damage due to overvoltage or transient voltages.

Difference between Zener and TVS diode

People often think that TVS diodes and Zener diodes are the same, but they serve different purposes and are made differently.

  • Zener diodes help to regulate voltage and operate in the breakdown region, while TVS diodes are designed specifically to suppress transient overvoltage spikes. Hence its electrical properties are more suited for this kind of application.

A TVS diode typically has a high impedance, meaning that only very little current(called leakage current) flows through it when reverse-biased. So TVS diode only conducts when there is a voltage transient that exceeds its avalanche breakdown voltage.

  • The second most important difference between TVS and Zener diode is its fast reaction time. We know that transients occur anywhere from picoseconds to nanoseconds, so the response time of this diode must be very short.
  • TVS diodes offer a wide range of operating voltages to accommodate the highest possible transient spikes in any electrical and electronic circuit.

So overall, TVS is more efficient than Zener diode in terms of properties like low clamping voltage, high operating voltage, low capacitance, less leakage current, and very fast response time.

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