Then many audio designers are wrong.squarewave said:Diverting into power supply rails doesn't make as much sense to me.
Then many audio designers are wrong.squarewave said:Diverting into power supply rails doesn't make as much sense to me.
squarewave said:Diverting into power supply rails doesn't make as much sense to me. I think it makes the most sense to place protection diodes right next to pins (between 2 and 1 and 3 and 1) and then use the XLR sockets that have the metal spike that connects pin 1 to the chassis so that shocks or whatever transients will be shunted directly into the chassis without getting that far inside the enclosure.
It's not random. I use 16.7V TVS diodes right now. ICs almost always already have protection diodes. The problem is that often times they can only handle low-energy transients. TVS diodes are designed to handle the high energy transients that can actually damage the IC.Monte McGuire said:Sure, you can choose some random voltage and pick a TVS part that clamps to that voltage, but won't you then be clamping to some arbitrary voltage, not based upon what the circuit can handle, but which TVS part you bought?
It all depends on the capacity of the EMC source to deliver energy. 1kV from a typical low capacitance EMC source is clamped by a mere 100pF cap.squarewave said:What happens if it's a 1kV spike - can the caps handle that? Could it cause an arc to another trace that is routed too close?
It's not an argument if no one presents arguments. So far the only real argument was posited by Monty who argued that the voltage should be relative to the device that is being protected. Ok. That makes sense. It's really not that compelling IMO but it is a valid argument. Most of the other replies seem to lean on "this is a very old and well inspected topic" that apparently everyone should already know. So then what's the point in asking questions on a forum? And telling people to search through forums has always been a weak punt IMO. If someone provides a good detailed answer to a specific topic, then provide a link to that post. But forum discussions very rarely answer questions completely or directly and group wisdom evolves over time. New parts become available. Are low-capacitance TVS diodes new? If yes, then maybe they should be considered? Why shunt transients into the rails if you don't have to? Do low capacitance TVS diodes meet all of the requirements for protecting circuits? If no, please explain why because so far I have not heard any arguments about that. I actually don't know myself. I'm just going on what the datasheet says.JohnRoberts said:This is a very old and well inspected topic.
Arguing with an experienced designer like Abbey is not productive. What he said again.
JR
semanticssquarewave said:It's not an argument if no one presents arguments.
In fact it needs to be clamped to less than device power terminal voltages to prevent unintended conduction paths (like intrinsic diodes.) For low to modest voltage applications it is not unusual to clamp directly to ground, but lots of hand wringing over stray capacitance and perhaps nonlinear impedances (with voltage) on high integrity inputs.So far the only real argument was posited by Monty who argued that the voltage should be relative to the device that is being protected. Ok. That makes sense.
yupIt's really not that compelling IMO but it is a valid argument. Most of the other replies seem to lean on "this is a very old and well inspected topic"
that Abbey surely knows.that apparently everyone should already know.
If you go back and look at my several answers I did not make that suggestion yet..So then what's the point in asking questions on a forum? And telling people to search through forums has always been a weak punt IMO.
I have never had to use a specialized TVS diode in decades of (audio) design... in fact I had to google it to understand the acronym. I have seen them used on telephone lines, and perhaps cable tv boxes where transient hazards are more common (but I never designed one of those either.)If someone provides a good detailed answer to a specific topic, then provide a link to that post. But forum discussions very rarely answer questions completely or directly and group wisdom evolves over time. New parts become available. Are low-capacitance TVS diodes new? If yes, then maybe they should be considered? Why shunt transients into the rails if you don't have to? Do low capacitance TVS diodes meet all of the requirements for protecting circuits? If no, please explain why because so far I have not heard any arguments about that. I actually don't know myself. I'm just going on what the datasheet says.
JohnRoberts said:Yes back to back (anti-parallel) diodes to ground from the - input is simple and effective with inverting amps, BUT you said non-inverting in your original post.
Also using JFET gate diodes as low leakage diodes is another old trick if the cost is acceptable.
JR
squarewave said:Ick! They have super high capacitance. I measured 625p. Strangely most of the SMBJ15CA datasheets don't mention anything about capacitance and I chose the part because it was used in the schematic for an eval board for some fancy audio chip. Only the OnSemi datasheet has a graph of capacitance vs reverse voltage. I guess modern designs assume everything is being driven by low Z. The source Z would have to be in the 5K ohms range to start seeing distortion though. I suppose I can keep using them for the moment. It seems there are TVS diodes with much lower capacitance (like CDSOD323-T15C which is only ~3pF).
Attaching diodes to supply rails is a PITA. It would be nice if I could find a simple 2 terminal part.
Thanks for pointing this out. I would like to interface with high Z gear.
squarewave said:I think a bi-directional TVS diode is essentially like back-to-back zeners. They have a reverse breakdown voltage.
squarewave said:Diverting into power supply rails doesn't make as much sense to me. I think it makes the most sense to place protection diodes right next to pins (between 2 and 1 and 3 and 1) and then use the XLR sockets that have the metal spike that connects pin 1 to the chassis so that shocks or whatever transients will be shunted directly into the chassis without getting that far inside the enclosure.
bluebird said:I say just socket the op amp... 8)
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