testing a TVS diode - Page 1
Forum section: electronics / beginners

author: jhjove
author_rank: Newbie
timestamp: October 12, 2022, 03:35:52 pm
content: How do I test a TVS diode with a DMM?Or more correctly, how do I test a stacked-die TVS diode?The diode in question is a Littelfuse 30KPA102A (uni-directional). In the circuit there are 6 used; 2 sets of 3 in a series configuration.I removed the diodes from the PCB to get a more accurate DMM diode Fwd bias reading. So 5 of the 6 range from 1.56V to 1.59V.The remaining diode reads 0.538V.The spec sheet from Littelfuse only mentions multi stacked die (4 or 5) in the Vf graph curve, there is no direct correlation to a part type.So my best guess is the diodes that read 1.56V to 1.59V are 4-stacked die and OK. The other diode has 3 failed PN junctions and is overall a failed part.Does this make sense?Thanks,Joe

author: mag_therm
author_rank: Frequent Contributor
timestamp: October 12, 2022, 03:57:03 pm
content: Use a bench power supply with current limit set to 10 mA or so, and wind up the voltage from zero until current flows.I just did this on a SLD15-018.DUT will overheat in a few seonds if current limit is set too high.eg 15 V * 100 mA = 1.5 Watt.

author: jhjove
author_rank: Newbie
timestamp: October 15, 2022, 01:08:01 pm
content: Using a power supply and monitoring the current then reading the voltage drop across the diode is sort of what my meter is already doing for "diode" mode.The SLD15-018 diode spec doesn't have any reference to minimum Vf. And does not seem to have any reference to multi stacked die (which is the main issue I'm researching).TVS diodes can be used in series to increase the clamping voltage. But it's the internally stacked ones I'm trying to verify.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: October 16, 2022, 02:13:30 am
content: Put a resistor between the TVS and GND. Probe between the resistor and the TVS. Increase your voltage until you get a reading.

author: strawberry
author_rank: Super Contributor
timestamp: October 16, 2022, 04:57:58 am
content: some cheaper power supply have larger output filter capacitor, enough to blow sensitive parts

author: Ian.M
author_rank: Super Contributor
timestamp: October 16, 2022, 06:30:07 am
content: OTOH a TVS diode capable of withstanding a 183A peak pulse current is scarcely a 'sensitive' part.The only way to be certain the O.P's 30KPA102A TVS diodes are good is to set up to measure their reverse breakdown voltage to check its in the range 113.90V to 125.29V @ 5mA Ir. An adjustable power supply >125V is obviously needed, and it should have a series resistor to limit its short-circuit current.If you haven't got anything better, (and assuming the typical USA 120V mains supply,) rig a Variac to feed a voltage doubling rectifier into a pair of matched 250V electrolytic reservoir capacitors (with 100K bleeder resistors across each of them), and a pair of 18K 3W wirewound resistors, one in series with each output wire to limit the short-circuit current (and reduce the risk of electrocution). That will give you up to about 10mA and a max of a bit under 400V DC (depending on the Variac's boost limit), plenty for testing a TVS diode of this type. Rig it up to the TVS diode with a high impedance voltmeter across it and a milliammeter in series with the DC supply, and wind up the Variac slowly till you see the diode current start to increase, stopping when it reaches 5mA to measure the breakdown voltage. Obvious safety concerns apply - high voltage DC is *NOT* forgiving and unless an isolation transformer is used upstream of the Variac the whole circuit must be treated as mains LIVE. A similar arrangement can be used in 230V mains countries, differing only in the use of a bridge rectifier and a single 400V reservoir capacitor, but must be treated with even greater respect due to the higher mains voltage.If the O.P. doesn't have either an adjustable HV DC PSU or a Variac + the experience to use it safely, he's S.O.L. and the only options would be to replace all the TVS diodes (and they aren't cheap) or take the job to someone who has the equipment and experience to do it right.

author: jhjove
author_rank: Newbie
timestamp: October 19, 2022, 11:58:49 am
content: Thanks for the detail on a breakdown test. I may create a test rig and try this on the part I have.But yes, these are not cheap, replacements are in the $20 USD range per diode.FWIW I sent an email to Littelfuse to try and get a understanding if these parts can be single junction or multi stacked junctions regardless of the binning...as long as the spec is maintained.But no reply.

author: jhjove
author_rank: Newbie
timestamp: October 24, 2022, 03:18:48 pm
content: Quote from: Ian.M on October 16, 2022, 06:30:07 amWell I did my test rig and the diode test current of 5mA lands smack in the the middle of Vbr min-man @120VSo definitely a good diode.Again thanks for the simple test method.