Low Capacitance Tranzorb in the 10-30V range
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From: mook johnson on 26 Jan 2010 18:55 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.
From: Tim Williams on 26 Jan 2010 19:09 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: http://webpages.charter.net/dawill/tmoranwms "mook johnson" <mook(a)mook.net> wrote in message news:jiL7n.22516$CM7.433(a)newsfe04.iad... > 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. > > > >
From: John Larkin on 26 Jan 2010 20:44 On Tue, 26 Jan 2010 17:55:58 -0600, "mook johnson" <mook(a)mook.net> wrote: >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. > > > Tripped on this while looking for something else: http://www.centralsemi.com/product/smd/select/diodes/ESD_UltraLowCapacitance.aspx 17 amps, 400 watts, 1.2 pF. I have no idea how many joules it can absorb. John
From: Joerg on 26 Jan 2010 21:34 mook johnson wrote: > 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. > 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: http://www.microsemi.com/micnotes/122.pdf 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. -- Regards, Joerg http://www.analogconsultants.com/ "gmail" domain blocked because of excessive spam. Use another domain or send PM.
From: mook Johnson on 28 Jan 2010 22:52
On 1/26/2010 8:34 PM, Joerg wrote: > mook johnson wrote: >> 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. >> > > 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: > > http://www.microsemi.com/micnotes/122.pdf > > 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. |