Hi everyone, I'm trying to understand the difference between a TVS diode and an ESD suppressor but honestly I'm having a bit of trouble because on some application notes online it says that they are the same thing... while on others there are separate categories

From what I understand, the main differences are:
----------------Diodes TVS:--------------
- Silicon avalanche diodes
- low capacitance, fast response time
- protect both power lines and high-speed data lines well
- surge energy rating low-medium-high

----------------Suppressor ESD:--------
- polymer structure
- low capacitance, fast response time (like TVS diodes)
- surge energy rating low


In concrete terms, in practice, if I find myself on the LittleFuse website, for example, when should I opt for one and how much for another?
Can you please give examples where you preferred one over the other?
Perhaps with today's technology, a TVS diode does exactly the same thing as an ESD protector?

It's a theoretical question, I don't have a practical example to give... maybe you tell me one and we can make it up just to understand the difference well

 

Both diodes are kinds of zener diodes.

The typical TVS diode (or TRANSZORB (TM)) is designed to protect power supply lines from overvoltage transients. Depending on the mechanical size of the diode they are able to absorb some kW(!) of power for a duration of some 100 us. This is usually enough to trip a fuse in front of the TVS and therefore to protect the circuit behind it. They react on pulses with rise times below 10 us. These diodes come in package sizes of 6 mm * 8 mm for a 3 kW type.

An ESD pulse is a totally different kind of pulse. It has rise time of a few ns, and a duration of maybe up to 100 ns and voltages of some kV but a low energy. Therefore these diodes are designed to withstand and absorb extremly fast transients especially on data lines but the don't need to absorb so much energy. Therefore they are packaged in small, low inductance housings and they can never ever withstand a pulse a typical TVS diode is designed for.

 

Both diodes are kinds of zener diodes.

The typical TVS diode (or TRANSZORB (TM)) is designed to protect power supply lines from overvoltage transients. Depending on the mechanical size of the diode they are able to absorb some kW(!) of power for a duration of some 100 us. This is usually enough to trip a fuse in front of the TVS and therefore to protect the circuit behind it. They react on pulses with rise times below 10 us. These diodes come in package sizes of 6 mm * 8 mm for a 3 kW type.

An ESD pulse is a totally different kind of pulse. It has rise time of a few ns, and a duration of maybe up to 100 ns and voltages of some kV but a low energy. Therefore these diodes are designed to withstand and absorb extremly fast transients especially on data lines but the don't need to absorb so much energy. Therefore they are packaged in small, low inductance housings and they can never ever withstand a pulse a typical TVS diode is designed for.

Thank you very much for your reply. I’d like to take this opportunity to ask where "varistors" fit in between TVS and ESD .. I’m a bit confused about them too.

 

Varistors generally have a much higher capacitance, some 100 pF to some nF. They are also used for protecting power supply lines. For data lines their capacitance is far too high. Quite often varistors are used as a coarse protection device in front of a TVS diode. Also the V/I characteristics are not as flat as those of a TVS diode. You should compare some data sheets.

ESD suppressor diodes are usually used to protect data lines (e. g. USB) against damage by ESD discharge.

 

Varistors, as mentioned above, are significantly slower than silicon based suppressors.
But on the other hand, they have higher energy clamping capabilities per unit of volume, and are inherently bidirectional.
Thus, they are mostly used to protect circuits connected to the AC power line.

A superior suppression strategy uses several different cascaded devices.

 

Both diodes are kinds of zener diodes.

The typical TVS diode (or TRANSZORB (TM)) is designed to protect power supply lines from overvoltage transients. Depending on the mechanical size of the diode they are able to absorb some kW(!) of power for a duration of some 100 us. This is usually enough to trip a fuse in front of the TVS and therefore to protect the circuit behind it. They react on pulses with rise times below 10 us. These diodes come in package sizes of 6 mm * 8 mm for a 3 kW type.

An ESD pulse is a totally different kind of pulse. It has rise time of a few ns, and a duration of maybe up to 100 ns and voltages of some kV but a low energy. Therefore these diodes are designed to withstand and absorb extremly fast transients especially on data lines but the don't need to absorb so much energy. Therefore they are packaged in small, low inductance housings and they can never ever withstand a pulse a typical TVS diode is designed for.

Varistors, as mentioned above, are significantly slower than silicon based suppressors.
But on the other hand, they have higher energy clamping capabilities per unit of volume, and are inherently bidirectional.
Thus, they are mostly used to protect circuits connected to the AC power line.

A superior suppression strategy uses several different cascaded devices.

Hello everyone again.
I’ve got a couple of questions that are probably a bit silly:

1) How do I know whether I need ESD or TVS protection? What questions should I ask myself? Should I consider the magnitude (amplitude) and speed of any potential pulse? If so, that depends on the context and the system in which the PCB is used… right?

2) Can I use both ESD and TVS?
Let’s take a practical example:


I have used only a TVS diode to protect Vin = [42V – 50V] which draws a maximum of 4A DC and has 15A inrush:


Can I also fit an ESD suppressor? If so, where does it go? In parallel?

 

ask yourself
how much is going to cost or inconvenience user until normal function is restored. if it is disposable thing (like fuse or relay) you can have them socketed so they are easy to replace. other than that you want protection.
is this sending/receiving signals from outside? (connector etc.). any time external wire connects to your board (power or signal), you will want to ruggedize/protect that termination point.
is it possible to reverse polarity (by mistake or intentionally)? if yes you would want to protect that to prevent damage.
is this going to be used as open board? (no housing) such as DIR rail carrier shown below? if yes then touching board and components is guaranteed and that is when you want additional protection... or actual enclosure. etc.

once you have the needs determined, you need to decide how... you need to know something (assumed or measured) about the circuit, and needed reaction time, capacitance etc. data line protection devices are usually arrays of TVS in single small package and have very low capacitance. power TVS protecting power rails are usually massive and single channel

vs.

 

As already mentioned: ESD suppressors are for protecting SIGNAL lines (e. g. USB) since they are ultra fast acting and designed to absorb low energy with very short rise and fall times (sub ns to a few tens of ns range) caused by ESD events whereas true TVS suppressors (e. g. Transzorb TM) are for protecting POWER lines with much higher energy and peak power in the kW range.

 

For your example in post #6 you cannot use an ESD suppressor for D5, since it has not the ability to absorb the energy of a transient on the power line. Due to the small size you woldn't ever see the magic smoke out of your ESD suppressor. You need a real big TVS diode which can handle up to 1.5 or even 3 kW peak power. Unfortunately: higher power means bigger components.

Usually TVSs are selected in such a way that their clamping voltage (@ 1 mA zener current) is higher than the maximum specified supply voltage of your device. The temporary clamping voltage at a few amps zener current should be well below the absolute maximum ratings of the omponents behind.

 

I have used only a TVS diode to protect Vin = [42V – 50V] which draws a maximum of 4A DC and has 15A inrush:

A TVS doesn't cause any inrush current as long as it is properly selected for the occuring voltages. A TVS is a VOLTAGE protection device. Under normal operating conditions the current through a TVS should be below 1 mA. The inrush current shown in your screenshot is caused by charging capacitors, ramp up current of DC/DC converters or whatever you have behind your TVS but never caused by the TVS.

The current through a TVS is always caused by overvoltages, which are clamped by the TVS.

 

There is another category of devices called varistors, which are not at all related to ZENER DIODES. They are typically breakdown devices, originally metal oxide barrier resistors, that transition to a conductive state at some voltage level. Many of them will stay in that conductive state after the over-voltage condition has passed. There are also gas-tube devices for higher voltages. They offer the benefit that they can return to the non-conducting state when the applied voltage is temporarily removed. I have used such devices to protect mains power inputs of equipment. They may be paired with over-current circuit breakers to provide automatic recovery after the over-voltage has passed. They are neither small nor cheap, but they are effective, usually.