I'm sorry, I meant to reply sooner and forgot.
In the top waveform at #39, did you still have the freewheeling diode right across the solenoid coil?
In that circuit, it it is as I think it is, the conventional diode on the breadboard would really only protect against the drain of the FET being pulled negative with respect to ground. It looks a bit like it may have gone into reverse breakdown at around 300 V. Generally diodes not intended to be avalanched don't like it much and are given to failing short-circuit.
It is hard to come up with a power rating for a TVS. Given the repetition rate, it is very likely that the average power rating really isn't important, but the peak current rating is. If the diode across the solenoid coil is used, then it will handle most of the energy stored in the solenoid's inductance, leaving only a small amount of energy for the TVS across the FET. I presume, however, that in the interest of parts count it may be preferable to omit the diode across the coil and let the TVS handle all the energy. Most of the energy will actually be dissipated in the coil's resistance.
The peak current in the TVS will be equal to the peak current in the FET at the instant of turn-off, so about 180/1111 = 162 mA.
Unfortunately, TVS diodes often aren't terribly well specified. There will be numeric values for "standoff voltage" and minimum and maximum breakdown voltages and for peak clamping voltage, but the the matter at hand, the latter is at higher current than required. It is safe to assume the clamping voltage will therefore be lower than spec'd but in the absence of curves, the amount is not easy to predict. The larger the die, the lower the clamping voltage for the same current.
The SMBJ170D might be appropriate. The standoff voltage is nominally only 170 V, but the minimum breakdown is 192 V. The maximum clamping voltage is 270 spec'd at 2.33 A (from Vishay datasheet). The standoff voltage may be too low. The next rating up has a clamping voltage well above the FET;s rating. I wouldn't be too concerned given the peak clamping current requirement and the fact that if a FET manufacturer rates a part at 250 V, it will be safe at a full 250 V - but I'd prefer to see some curves for the TVS.
This, from Littelfuse has some helpful general info. I can't find anything at Vishay that is similar, though I know the company that Vishay acquired that produced the original TranZorbs had some useful ap notes. Bourns may have something useful.
www.littelfuse.com/~/media/electronics/product.../littelfuse_tvs_diode_catalog.pdf.pdf
In the top waveform at #39, did you still have the freewheeling diode right across the solenoid coil?
In that circuit, it it is as I think it is, the conventional diode on the breadboard would really only protect against the drain of the FET being pulled negative with respect to ground. It looks a bit like it may have gone into reverse breakdown at around 300 V. Generally diodes not intended to be avalanched don't like it much and are given to failing short-circuit.
It is hard to come up with a power rating for a TVS. Given the repetition rate, it is very likely that the average power rating really isn't important, but the peak current rating is. If the diode across the solenoid coil is used, then it will handle most of the energy stored in the solenoid's inductance, leaving only a small amount of energy for the TVS across the FET. I presume, however, that in the interest of parts count it may be preferable to omit the diode across the coil and let the TVS handle all the energy. Most of the energy will actually be dissipated in the coil's resistance.
The peak current in the TVS will be equal to the peak current in the FET at the instant of turn-off, so about 180/1111 = 162 mA.
Unfortunately, TVS diodes often aren't terribly well specified. There will be numeric values for "standoff voltage" and minimum and maximum breakdown voltages and for peak clamping voltage, but the the matter at hand, the latter is at higher current than required. It is safe to assume the clamping voltage will therefore be lower than spec'd but in the absence of curves, the amount is not easy to predict. The larger the die, the lower the clamping voltage for the same current.
The SMBJ170D might be appropriate. The standoff voltage is nominally only 170 V, but the minimum breakdown is 192 V. The maximum clamping voltage is 270 spec'd at 2.33 A (from Vishay datasheet). The standoff voltage may be too low. The next rating up has a clamping voltage well above the FET;s rating. I wouldn't be too concerned given the peak clamping current requirement and the fact that if a FET manufacturer rates a part at 250 V, it will be safe at a full 250 V - but I'd prefer to see some curves for the TVS.
This, from Littelfuse has some helpful general info. I can't find anything at Vishay that is similar, though I know the company that Vishay acquired that produced the original TranZorbs had some useful ap notes. Bourns may have something useful.
www.littelfuse.com/~/media/electronics/product.../littelfuse_tvs_diode_catalog.pdf.pdf