Transil - please help me understand the principle of operation?

"transil is something similar to a zener diode, but if you run the zener diode for even a millisecond
current 40A, it will probably burn, and the transil will withstand it. I don't know how exactly transiles behave
available relatively cheaply in the trade if overloaded - perhaps (that would be best) they give
for a moment, a complete short circuit (and therefore they do not heat up any more), and when they cool down, they become zeners again. Or
they can stay together forever... in any case, the characteristics of the transil are given in the data sheet until
current is small, it behaves like a zener for some voltage, e.g. 6.8V, and at very high currents, such as
tens of amperes, the voltage can reach up to 13V"

I mean the bold text - what is it like?

A bit of theory.
Transil protection diodes

Due to the need to dissipate high impulse energy, protection diodes are characterized by a large pn junction area and have heat sinks connected to the semiconductor structure. In the absence of an overvoltage, the diode has the rated line voltage; when an overvoltage occurs, after exceeding the breakdown voltage, the diode enters the avalanche multiplication state. The diode resistance value decreases rapidly below 1 Ohm. A surge pulse flows through the diode. An impulse reaches the protected device, the amplitude of which is limited to a safe value. These diodes are produced in a wide power range (400 W-15 kW). The disadvantage is the relatively large capacitance (10 - 15000 pF), which limits their use to frequencies of 100 MHz.

Typically, two push-pull diodes are used as limiting elements. Both Zener diodes and protection diodes are produced in this way. Thanks to this, the device is protected against overvoltages of positive and negative polarity.

I want to use this transil in a transformerless power supply system instead of a zenar diode, so capacity is not a problem https://www.elektroda.pl/rtvforum/topic407021.html
After all this, is the transil damaged or should it return to its previous properties - because that's what I wanted?

Surge protection components must not adversely affect the operation of the device. After the stroke disappears, the transil returns to its previous properties. Just in case, you can check with a meter whether the diode is not short-circuited (usually diodes "do" for short-circuit).

Approx! Thanks

A bit of an old topic, but I'll piggyback on it.

The question concerns transil, the power supply protection system looks like below



I assume that I used the SMBJ12A transil, so its parameters are:

Reverse Stand off Voltage - 12V
Breakdown Voltage min - 13.3V
Breakdown Voltage max - 14.7 V
Maximum Peak Pulse Current - 30.2A

I now assume that the Breakdown Voltage in this element used is 14V. I understand that at this voltage the transil starts to conduct (depending on the manufacturing tolerance of the item) and shorting the circuit burns the resistor. How will such a protection system behave in the range of voltages below this Breakdown Voltage and above this Reverse Stand off Voltage?

It's 2017 and I'm looking for this too...

My colleague from post #6 drew the wrong conclusions.
Transil (or TVS) works like a Zener diode, above a certain voltage it starts to conduct, transil is not an ideal element, it has a certain dynamic resistance, the higher the current, the higher the voltage. When an overvoltage occurs with energy greater than the allowable limit, the transil will be permanently damaged - usually a short circuit.

Thanks for the answers. I thought about:

marcin w wrote:

How will such a protection system behave in the range of voltages below this Breakdown Voltage and above this Reverse Stand off Voltage?

So like a Zener diode. It's a pity that there is no current-voltage relationship on the graphs. But I understand that when approaching Breakdown Voltage you can expect a current of several mA?

From the posts above, everything is clear and logical to me, but... I came across such a case. What did the poet mean????
The patient is the automation controller, some inputs/outputs have disappeared, there is no power to the operational amplifiers.
The system is based on a 7805 smd 8 pin stabilizer, the diode in question is BUM GP716, the internet is silent, I assume it is a bidirectional 17v one


The effect is that the stabilivolt has no ground reference point and does not work, nothing heats up
the diode on the diode test behaves like a normal unidirectional diode, I thought it was in one direction, I soldered it in the opposite direction and nothing.

I don't understand this way of using transil

This is a quite common way to increase the output voltage of the stabilizer. Most often, it's about gaining a little height. For example, the stabilizer is at 3.3V and the diode is connected in the forward direction (voltage ~0.65). The output will be 3.3+0.65=~4V. 3.3V stabilizers are cheap and easily available. The same cannot be said about the 4V ones.

However, yesterday's fatigue came out today and I used to increase it with regular diodes
Thanks

Hello
Can I refresh the topic?

Added after 8 [minutes]:

Can bidirectional transil be used as surge protection?
E.g. 1.5KE300CE on a 230V AC network.
A voltage spike above 300V will create a short circuit and turn off the fuse.
Regards

Added after 2 [minutes]:

Power 1500W, won't temporary overvoltages destroy it, in the order of a few milliseconds?

1.5kW refers to 10us, and 1.5kW is nothing compared to what a 230V network can deliver, although transil has better characteristics than a varistor, it will not replace a varistor in network applications. Finally, what matters is how much material there is to absorb the surge energy, in transila it is a silicon flake which is maybe 1 mm3, in a 20 mm varistor it is closer to 1 cm3.

Is this a fact, so when there is an overvoltage, the transil will explode?
Assuming about 1 ohm of the short-circuit loop, I get about 50 kW of short-circuit power.
And the varistor?

marekch2 wrote:

Is this a fact, so when there is an overvoltage, the transil will explode?

Good question, I have never seen a transil in a network circuit, so I have not seen what a failure looks like. If the overvoltage exceeds the transil's endurance, it will create a short circuit, I am afraid that the network short circuit current may burn out the "short circuit", it is not a metallic short circuit and at several hundred amperes a lot of power will be released. Transistors through which the network short-circuit current flows usually explode, diodes rarely explode.

Varistors are a popular solution, although they are not precise in limiting overvoltages and wear out.

Quote from another topic:

I measured the "275L20" varistor.
Diameter 15.3 mm, thickness 2.9 mm.
I just bought these yesterday - 5 pcs.
AC current consumption.
275V - 56 uA
330V - 3.6 mA
350V - 10 mA
370V - 37 mA
400V - approx. 100 mA.
The time after which the varistor will short-circuit depends on the heat released. (physics)
In the case of the varistors I measured, 400V AC was about a second.
However, 390V AC is quite long - a few seconds.

I have 15.3 mm / 5.25 mm varistors at home, but for a different voltage.
Varistors differ in power and energy absorption capacity.
The characteristics are the same.

This means that these thicker varistors will have a longer response time to short circuit.
A more powerful varistor provides less protection.
It makes no sense, but...
Working a varistor until a short circuit is not its normal use.
This is normal - the varistor has to absorb energy without being destroyed.

From this conclusion for me the conclusion is better to let it explode, but in a short time it will disconnect the power.

marekch2 wrote:

From this conclusion, for me, it is better to let it explode, but it will disconnect the power supply in a short time.

If the short circuit is strong enough not to make a break or let the overvoltage through, it's ok.

You can also consider a "crowbar" on the triac, where the short circuit is made by an element with parameters selected so that it can withstand without damage, an additional series resistor will reduce the short-circuit current, it can be used if the receiver does not consume much.

marekch2 wrote:

Is this a fact, so when there is an overvoltage, the transil will explode?

Yes, it will explode and "spray" covering everything in the area.
Pieces of metal were embedded in the porcelain.

jarek_lnx wrote:

You can also consider a "crowbar" on the triac, where the short circuit is made by an element with parameters selected so that it can withstand without damage, an additional series resistor will reduce the short circuit current

But this resistor must be connected in series with the receiver.
It will heat up.
An L-PE (LN) short circuit on one phase means 400V AC applied to the other two phases.
It can cause damage.