Increasing DESAT diode voltage rating - Page 1
Forum section: electronics / projects

author: rubacava
author_rank: Newbie
timestamp: June 02, 2024, 04:51:31 pm
content: Hello,I wonder if it's possible to increase the total reverse voltage rating of the DESAT protection by connecting multiple diodes in series. To my knowledge, multiple diodes will have different reverse leakage characteristics will fail one by one if one them exceeds the rating. In the 10.2.2.8 DESAT Diode and DESAT Threshold section ofhttps://www.ti.com/lit/ds/symlink/iso5451.pdfIt mentions that multiple diodes can be used to increase the total voltage rating. Does reverse leakage don't matter for DESAT protection or I am missing something?Best Regards.

author: Marco
author_rank: Super Contributor
timestamp: June 02, 2024, 05:45:13 pm
content: As long as you go slowly, avalanche in PN diodes is not significantly negative resistance and not destructive as long as the power stays small. Before any significant current can flow, they have to both get above their avalanche voltage.Does the circuit go slowly enough? Apparently.

author: David Hess
author_rank: Super Contributor
timestamp: June 02, 2024, 06:22:46 pm
content: It should not matter because that level of leakage will not damage the diode. While the collector voltage is rising quickly, the voltage across the diodes in series will be determined by their capacitance anyway.If you are worried about this, you could use avalanche rectifiers which are processed to make sure that their junction breaks down evenly.

author: rubacava
author_rank: Newbie
timestamp: June 02, 2024, 06:56:21 pm
content: How about collector voltage in it's stable state and higher than the rating of a single diode in the network? Since it's basically a charged capacitor can't it still exceed the breakdown voltage?

author: David Hess
author_rank: Super Contributor
timestamp: June 02, 2024, 09:29:18 pm
content: Quote from: rubacava on June 02, 2024, 06:56:21 pmSure, the leakage of the diodes will not match exactly, so some diodes will reach their breakdown voltage and their leakage will increase, but this will not damage them.

author: rubacava
author_rank: Newbie
timestamp: June 03, 2024, 03:37:14 am
content: It's kind of strange that driver IC datasheets don't mention the use of Avalanche diodes. Thanks for the replies it makes sense how they work.

author: David Hess
author_rank: Super Contributor
timestamp: June 03, 2024, 06:00:59 am
content: Quote from: rubacava on June 03, 2024, 03:37:14 amAvalanche diodes are really intended for power applications where the reverse current will be high for a short time, like with inductive load switching. In a normal diode, hot spots will form in the junction under these conditions which can damage the diode. Avalanche diodes are processed so that the junction breaks down uniformly preventing the formation of hot spots.In this case the only disadvantage of using an avalanche diode is that it will be larger than necessary so have more capacitance than necessary, because they are intended for power applications. The smallest ones I commonly see have 1 amp ratings and 25 nanosecond reverse recover time. There are parts however like the SF1600 which are 1600 volts, 1 amp, and 75 nanoseconds.