duty which comes to 30mW.
Of course not continuously. That's why I wrote "for a few hundred msec". As mentioned before, the duty cycle will be extremely low, and it'll be less than 0.01%.
I am not going to sink 300W pulse into them but maybe 1-2W pulses.
-- Regards, Joerg http://www.analogconsultants.com/
0.01% duty which comes to 30mW.
Okay , from Fig 5.
As i vaguely remember, a TVS is a crappy limiter, with a slow limiting slope and high incremental resistance reminiscent of that seen for a 2.7V or 3.3V zener or like that of a forward biased diode. Use a real zener with a current limiting resistor in series so that it will not blow out.
That is exactly what I meant. It is a non-issue _if_ you know how much it will conduct at 80V, worst case maximum. And I don't, hence my inquiry and my post here.
-- Regards, Joerg http://www.analogconsultants.com/
Zeners would be (somewhat) better but, for example, a 82V zener in an SMA package can only take 55mA of surge current and only for less than
10msec non-repetitive:-- Regards, Joerg http://www.analogconsultants.com/
You could try a gas discharge tube as a first line of defence, there are some tiny surface mount ones around now which trip around 70V, and then clamp around 20V. Can take amps for much longer than a TVS.
Gas discharge?
Cheers
If you don't want 80V conduction, use the next higher voltage in the range. This is guaranteed not to conduct below 85V.
If the aim is to protect your hardware, design it to do so. A dead TVS is worse than no TVS.
RL
Characterize the ringing for worst case energy content, and stop using vague generalizations.
Can you damp the 'low energy' ringing?
Real estate reduction possibility = two signal diodes and a single clamp / energy storage rail that means business, or capacitively-couple a thyristor-type structure with more benign single-fault characteristics.
RL
As I mentioned, exactly that is what I can't do. A 85V TVS will not conduct in any significant way until the voltage is way past 110V, and tha's above abs max here.
Can't be done differently, no space for a cut-out circuit. A TVS does not have to die here, provided its current at 80V is modest enough. The spike bursts will be short and very low duty cycle, as in "once in a blue moon". Energy above 80V is small, but not quite small enough for a zener.
All I need is hard data, like "guaranteed not to exceed 50mA at 80V". I am sure that data exists but it didn't make it into the datasheets. Same with zeners but there I was able to obtain such data from a small mfg.
-- Regards, Joerg http://www.analogconsultants.com/
When clamped hard to 90V with it is about 10A into the clamp, for around
60usec.
Unfortunately not in this case. It is due to stuff outside my circuitry.
The clamp device is the problem, it'll usually require a D2PAK or something that is similarly beefy.
-- Regards, Joerg http://www.analogconsultants.com/
Thanks, but those don't work because of the "90V +/-30%". At -30% that would result in kablouie and at +30% the electronics behind it would be dead.
-- Regards, Joerg http://www.analogconsultants.com/
That's what MArtin suggested but they huge tolerance makes those not useful. I only have the range of 80V to 100V to work in.
-- Regards, Joerg http://www.analogconsultants.com/
You could combine the precision of a zener with the peak energy handling of= the TVS to get your results- the zener sets the peak firing voltage, TVS i= s low voltage not critical except that its threshold for significant conduc= tion exceeds steady state worst case maximum DC on line with sufficient mar= gin so that SCR shuts off by holding current deprivation.
Please view in a fixed-width font such as Courier.
. . . . . . ----------+-----------+------------ . | | . | | . | | . ___/ ___/ . // \ // \ . --- ZD --- TVS . | | . | | . | | . | ----- . +---------/ \ SCR . | ----- . | | . [390] | . | | . | | . | | . ----------+-----------+-------------- . . . . . . . . . . . . . .
the TVS to get your results- the zener sets the peak firing voltage, TVS is low voltage not critical except that its threshold for significant conduction exceeds steady state worst case maximum DC on line with sufficient margin so that SCR shuts off by holding current deprivation.
That is a pretty good idea. Well, if I had the space for a big enough SCR. But there is another problem: The SCR will not let go until the TVS has largely come out of conduction and the decay of the 80V surges is going to be very slow. That would cook out the TVS.
So essentially I have to leave everything under 80V untouched or sink only a very small current whenever the circuit is below 80V. Just to avoid overheating any of the protective devices.
The main issue is the fast onset of the 80V surge which creates ringing. It's only this ringing I have to cap. So potentially I cold do something with a high-pass but ... no space.
-- Regards, Joerg http://www.analogconsultants.com/
the TVS to get your results- the zener sets the peak firing voltage, TVS is low voltage not critical except that its threshold for significant conduction exceeds steady state worst case maximum DC on line with sufficient margin so that SCR shuts off by holding current deprivation.
How about a surge-rated surface-mount series resistor and a shunt cap or zener? That's about what's in a telecom line network. There are lots of parts designed specifically for that application. I have some files around here somewhere, research I did for a friend...
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
the TVS to get your results- the zener sets the peak firing voltage, TVS is low voltage not critical except that its threshold for significant conduction exceeds steady state worst case maximum DC on line with sufficient margin so that SCR shuts off by holding current deprivation.
80 volt rail or what ever.| | + | | | '-' | +-----+
low side or back feed to the supply rail (created by AACircuit v1.28.6 beta 04/19/05
All that can be fitted in a small area..
I've used such circuit and it wells very well. Jamie
g of the TVS to get your results- the zener sets the peak firing voltage, T= VS is low voltage not critical except that its threshold for significant co= nduction exceeds steady state worst case maximum DC on line with sufficient= margin so that SCR shuts off by holding current deprivation.
The SCR can be a micro-dot, there's not enough voltage across it to cause a= ny heating at your currents.
g of the TVS to get your results- the zener sets the peak firing voltage, T= VS is low voltage not critical except that its threshold for significant co= nduction exceeds steady state worst case maximum DC on line with sufficient= margin so that SCR shuts off by holding current deprivation.
What is the ringing frequency? All you have told is that it lasts for 100s = milliseconds. You obviously do not have enough high frequency loss on your = input. The fix would then be a series ferrite bead with a high frequency ca= pacitor shunt to ground to kill the Q.
There'll be no Maynards on your job.
ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.