Gents.
I'm looking for a tranzorb or equivilent that can discharge a 45mH inductor with 1A DC flowing through it if one end gets disconnected. This tranzorb must have less than 100pF of capacitance. The tranzorb will be in parallel with the inductor.
any thoughts? All if the 1.5KE like parts have 800pF and up.
What voltage, dV/dt, dI/dt?
Can you just put an FR102 in series with the 1.5KE? Or skip the TVS and use a beefy capacitor and big ohm resistor? Big resistor means little effect under normal conditions.
Actually, since you want low capacitance, a 1N914 would probably take 1A peak for long enough (ms, us??). Rated for 200mA continuous IIRC. That's all of 4pF at low voltages, and close to SFA at more.
Tim
-- Deep Friar: a very philosophical monk. Website:
Tripped on this while looking for something else:
John
Not sure what you want to do but if the inductor is pulled down, held and then flies back until it leans into the TVS maybe the trick in figure 1b works:
But keep in mind that TVS devices are meant to snuff the occasional spike. Regular load dumps out of 45mH might be responded to with a loud
*PHOOMP* and some debris flying about. The last time I did a (transistorized) load dump for a roughly 20mH coil at a few amps the dump part needed to be heat-sinked. Without that it would have soldered itself right off the board.
Found some of the SA18 parts at digikey. Looks like the trick they use is to put a diode junction in series with the high capacitance zener junction. As long as the zener is not conducting the diode junction looks like a small capacitance in series with a large one so the net is a small capacitance.
The downside of course is you now need two devices do bidirectional.
no free lunch again but this will work since I only need to do this in one place. :)
Thanks for the input guys.
You can buy the dual device in a single package.
Well, this works... depending on what you're doing. If you have occasional large voltage swings, then it doesn't help at all. OTOH, if you have small AC voltages, or large voltage swings, but at such a frequency that the TVS parasitics have no time to discharge, then it'll work fine.
I see you want under 100pF. You might want to try several lower voltage TVSs in series if the above remark applies.
The capacitance looks huge, figure 4:
Keep in mind the C varies with applied V across the tranzorb. They sometimes quote C at the breakdown voltage, where it's much lower.
My bad its a SAC15 from litelfuse.
these are rated at 0 volts. usually gets lower with higher voltage.
Do you have a part number handy?
Ah, with diode built in. But you've got to use two per line, or a diode in the other direction if unipolar.
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