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23

The reason the same symbol is sometimes used for TVS diodes (Transorbs) and Zeners, is a Transorb has a lot in common with a Zener. An ideal Zener and an Ideal TVS-diode would be indistinguishable in their characteristics. This leads to ... laziness in library management (or ignorance) and the same symbol is used. Regulator Zeners and TVS-Zener diodes ...


22

It comes downto what are you trying to protect against There are four main types of transient suppression devices Gas Tube Protection time: > 1us Protection Voltage: 60 - 100V PowerDissipation: Nil Reliable Performance: No Expected Life: Limited Other: Only 50-2500 surges, can short powerlines MOV Protection time: 10 - 20ns Protection Voltage: > 300V ...


15

You have three components there that are all there for protecting the AVR, but all are doing a different job. The resistor is there to stop steady state high voltages. The capacitor is to remove ripple/RF/slow transients. The TVS is to suppress fast transients. In order to get the best out of your protection, you need to have the shortest (lowest ...


15

Varistors are "baked" semiconductors, their properties aren't tightly controlable. Think of them as a mesh of billions of Schottky junctions. Their big pro is they can both short a spike and turn it into heat smoothly because of the high mass of the actual mesh. In addition, as the varistor heats up, it gets more conducting and this can be used to blow a ...


9

Interesting question. In reality it probably does not matter much which side you put them on, however there are pros and cons to both. Connector Side PRO: As a general rule of thumb you want transient suppressors as close to the connector as you can so the voltage/current spike does not go very far on the PCB and has less chance to cross-couple into other,...


9

The most obvious difference is the continuous Pmax power rating for heat dissipation. 5 watts MOV vs 0.25 watts TVS Power vs signal vs location affects the disturbances and solutions available. This will not be a tutorial. Peak current MOV is better for high AC line surges for locations with unbalanced lines so 100A half wave at 60Hz Consider ...


9

You are mixing up two ESD solutions and mashing them together: Rail clamp diodes and TVS didoes. If you are using rail clamp diodes, then you do this: simulate this circuit – Schematic created using CircuitLab The rail clamp diodes ONLY clamp line voltages in forward bias. The line voltage is kept between \$ V_{dd} + |V_f| > V_{line} > GND-|...


8

I counted at least five questions in your question. I will try to answer only few. To begin, there are several levels of ESD events that can be specified by OEM of equipment, for different environment and other operating conditions, all classified in IEC 61000-4-2 standard. Then yes, connector design does play a significant role in failure rate of ...


8

First I'd like to stress that all microcontroller chips already have on-chip ESD protection, without that they would become almost impossible to handle. But it is indeed a good idea to add extra protection to pins which can be touched from the outside and/or interface with other boards etc. You can just treat the Analog pins the same way as the Digital ...


8

If you consider what the 8 kV ESD really is in terms of energy storage devices and resistors it'll look something like this: - Picture from here. The 150 pF capacitor is charged to +8,000 volts but, your target circuit doesn't actually receive that voltage directly; there is a 330 ohm resistor in the way. That means the peak current delivered can be up to ...


8

A TVS diode is typically capable of much higher power than ESD diodes. TVS - "Transient Voltage Suppression" can, if rated accordingly, be capable of suppressing surge pulses - these are pulses that have several hundred volts (and a generator capable of sourcing several hundred of amperes) for a few microseconds. A few microseconds might not sound ...


7

Resistors are useful before and after the TVS to serve different purposes. The cap may be placed either in parallel with the TVS or directly at the processor pin; the latter will provide somewhat more protection, but will also cause the processor to respond more slowly to changes in the input. If the input to the device were connected to a charged-up ...


7

Would you consider it likely that this thing is broken/damaged? Yes I would but, there are certain things you can decipher from the data sheet that might help you see why (such as this): - So, with an ESD discharge voltage of +8 kV, the TVS diode would limit the peak voltage to about 12 volts. To get deeper you have to look at what MIL-STD-883 is all about....


6

TVS diodes are used for transient overvoltage protection. You should not use a TVS for clamping a voltage continously. It is only for protection against voltage transients, A TVS diode is placed in parallel (not in series) with the power input that you want to protect, so, the 15A that you mention will not cross the TVS. You can see a TVS as a big ...


6

Yes, you should have ESD protection on all external connectors, including power, USB, audio, SIM cards, SD cards, etc. It is considered good practice to include them. ESD damage has become more of a problem as the geometries inside IC's shrink, making them more susceptible. I haven't seen any statistics on ESD damage, but I would guess -- and this is only ...


6

From the datasheet: Breakdown voltage, IO to GND is the critical parameter. Some parts may conduct at 4.5V, shorting the 5V VBUS to ground and other may not. This is not a suitable part for VBUS ESD protection.


5

Trying to clip this mess after the fact is the wrong way to start attacking this problem. The real problem is that there is loads of crap on the power supply. Find out why that is happening and deal with it at the source. Is this caused by ground bounce? If so, figure out why and address it. In that case it will be affecting other things too. Is it ...


5

To prevent induced or conducted (due to breakdown) spikes on other traces.


5

If you look at a parametric search for TVS diodes, you will see columns of the parameters that differentiate the diodes. The most important are breakdown and clamping voltage, peak pulse power/current, and whether the device is bidirectional. Bidirectional diodes are back to back diodes so that they can clamp both positive and negative voltages. For high ...


5

Robustness is a design choice you make. Is you compare a small PIC/74HC vs the SOC in a raspberry pi or PIC or other small 5V micro or 74HC logic: - small number of pins - plenty of room for wide metal tracks - high current pins 50mA capable = large fet area - true CMOS protection circuit - offloads static to the power supply with only diode drop - ...


5

You can use CEC (via HDMI) - I use libcec to turn my TV on and off with a RPi running a media centre. It also allows you to monitor the power state of the TV with the RPi.


5

In all likelihood, the site you linked to is simply using a generic picture for the entire P6KE series, which includes both unidirectional and bidirectional devices. As your second image shows, P6KExxCA devices do not have a direction marker. This excerpt from the datasheet provides further evidence of this. The unidirectional devices in the series do have ...


5

Question 1: What makes e.g. the TPSMA6L20A more suitable to this application than any standard SMBJ20A? I cannot find any appreciable differences in the datasheets. Immediately the main difference is one is SMA and the other is SMB. This indicates a different package size as well as power handling. However, the TP variant is the high reliability variant ...


5

In the anti-parallel configuration of your second diagram, one of the diodes will conduct whenever the source voltage exceeds its forward threshold voltage (0.6 V or so). This is usually not what you want. The reverse breakdown voltage, which is the whole point of a TVS, won't even come into it.


5

Like everything else in life the answer is: It depends Depends on the nature of the circuit (does it have highly inductive switching loads? Is it 'life-critical', or is it a McDonalds happy meal toy? Or is it the fuel regulation control for a 737 jet??) etc.. MOSFETs work just fine without them My company makes consumer products by the 100's of ...


5

I have done overvoltage testing on USB powered devices that contain TVS didoes. In my experience, they usually fail short when you do something like this. If it is not pulling down the 5V rail and it is not getting hot during normal (5V) operation, it probably hasn't failed yet. Then again, it may be damaged and ready to fail. If replacing it is an option I ...


4

Using a VCC rail in conjunction with unidirectional TVS diodes allows the device to ensure the data lines are clamped between the supply voltage and ground. This way, they can adapt to different supply voltages without requiring a separate device for each, and start clamping as soon as the voltage is more than a diode drop outside the rails. Another ...


4

The data sheet shows that the device can dissipate 6.5 watts on an Infinite Heatsink. The value you are using (75 degrees C per watt) is for dissipation to ambient (No Heatsink). So for dissipating to ambient, the device can't really dissipate 6.5 watts. Assuming 20 degrees ambient temperature, and you doing the math, you could only do 1.73 watts ...


4

As it says right in the datasheet, it can withstand 6.5W dissipation on an infinite heatsink. An unheatsinked chip will increase 75C per watt, limiting it to 2W before it reaches its maximum operating temperature. The point of a heatsink is to reduce its junction thermal resistance to some value less than 75 so that it can dissipate more power without ...


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