Can you place two MOSFETs in series to increase teverse breakdown voltage? - Page 1
Forum section: electronics / beginners

author: satyamfifa
author_rank: Regular Contributor
timestamp: August 17, 2022, 09:57:38 pm
content: Hey All,I want to use P-channel MOSFET to provide reverse polarity protection up to 32V, so can I simply use two 20V breakdown MOSFETs in series?Kind Regards,Sparsh

author: inse
author_rank: Super Contributor
timestamp: August 17, 2022, 10:12:42 pm
content: I think it would be easier to use one MOSFET with appropriate D/S voltage as you would have to supply a separate independent drive circuit for the second MOSFET.

author: niconiconi
author_rank: Frequent Contributor
timestamp: August 17, 2022, 10:41:09 pm
content: Yes, you can. But you must add static and dynamic voltage balancing circuits. First, to force the leakage current of each transistor to be equal, each transistor must have a megaohm resistor connected in parallel. This is called static voltage balacing (inevitably, the drawback is the creation of a high leakage current, since the resistors are always on). Otherwise an uneven leakage current means the transistor with the lowest leakage would experience the highest voltage and explode, the cycle repeats until all transistors are destroyed. Next, each transistor must also have a resistor-capacitor snubber network connected in parallel to suppress transient overvoltage at switching. This is called dynamic voltage balacing.This is usually a special technique for high voltage applications when suitable transistors are unavailable. It's not recommended for other uses.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: August 17, 2022, 10:42:49 pm
content: Should act like diodes in a series:https://www.daenotes.com/electronics/basic-electronics/diodes-in-series

author: Terry Bites
author_rank: Super Contributor
timestamp: August 18, 2022, 03:07:07 am
content: You certanly can. Adding the second MOSFET here doubles the breakdown point from -20 to -40V. but, as pointed out, why not use a 50V device from the start.The disadvantage of adding a seond device is that you double Ron.

author: Zero999
author_rank: Super Contributor
timestamp: August 18, 2022, 07:59:19 am
content: Quote from: Terry Bites on August 18, 2022, 03:07:07 amThat's true. An interesting thing to note about RONis, given a MOSFET die of the same size, it goes up by the square of the voltage rating, so a MOSFET rated to 40V will have four times the RONcompared with a 20V MOSFET of the same physical size.This doesn't change the fact it's normally just better to get a higher voltage, larger MOSFET. It's only worth connecting MOSFETs in series at voltages above 500V or so, but at that voltage IGBTs are often a better option.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 18, 2022, 09:00:56 am
content: Oi. Ron. Check this out!Well, never......

author: daqq
author_rank: Super Contributor
timestamp: August 18, 2022, 12:40:33 pm
content: It's done, but only when absolutely necessary and I've never seen it done at low voltages, since it comes with a lot of issues that need to be addressed with timing and balancing, gate driving...Behlke does it in their delightful high voltage modules (https://www.behlke.com/).

author: langwadt
author_rank: Super Contributor
timestamp: August 18, 2022, 01:55:28 pm
content: Quote from: niconiconi on August 17, 2022, 10:41:09 pmmosfets won't explode just because of over voltage, with overvoltage they avalanche like a zener with just leakage current that is very little power

author: satyamfifa
author_rank: Regular Contributor
timestamp: August 22, 2022, 03:05:27 am
content: Thanks everyone, I think I'll just stick to uising single MOSFET with high breakdown voltage