Do "ideal diodes" actually behave like "diodes"? - Page 1
Forum section: electronics / beginners

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: September 14, 2024, 03:52:02 pm
content: I've known about "ideal diodes" for a few years as a means to protect circuits from reverse-polarity, such as used likethis, however I've been wondering;Do "ideal diodes" actually behave likediodes? Do ideal diodes block reverse-current flow? If theloadis abattery, will the ideal diode actually prevent reverse-voltage flow?Thanks

author: ArdWar
author_rank: Frequent Contributor
timestamp: September 14, 2024, 04:02:31 pm
content: As always, if you use commercial one you should scrutinize the datasheet.Those advertised as ideal diode, OR-ing controller areusuallyreverse current blocking.Those advertised as reverse polarity protectionusuallyaren't reverse current blocking.Be aware that there are generally two kind of ideal diode implementation. Comparator-based, and constant linear drop-based.Comparator-based one usually are cheaper, but won't block until serious amount of current flow backward that it generate enough voltage on pass FET Rds(on) to trip the comparator.As for your circuit, no, it won't block reverse current. That's reverse voltage protection circuit, not ideal diode.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: September 14, 2024, 04:08:18 pm
content: Quote from: ArdWar on September 14, 2024, 04:02:31 pmWow, had no idea that there was actually different types of ideal diodes! Thanks. I guess myearlier exampleof an ideal diode using only a zener diode, P-FET, and resistor, would that be a simple "reverse polarity protectionwithoutreverse current blocking"?

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: September 21, 2024, 03:46:13 pm
content: Bump, just to quickly answer this?Quote from: LooseJunkHater on September 14, 2024, 04:08:18 pm

author: Kurets
author_rank: Regular Contributor
timestamp: September 21, 2024, 03:56:44 pm
content: Yes, think what happens if the right side is more positive than the left (ground is still zero). Mosfet will be on and current goes in reverse. Thus nit ideal diode, only reverse polarity protection.

author: MK14
author_rank: Super Contributor
timestamp: September 21, 2024, 03:59:24 pm
content: The following fairly recent video (11 minutes 39 seconds long), seems to be an interesting and informative guide to ideal diodes, and using them, in some application(s). Especially for anyone, who doesn't know much about them.

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: September 21, 2024, 04:09:12 pm
content: Quote from: Kurets on September 21, 2024, 03:56:44 pmFantastic, thanks!

author: LooseJunkHater
author_rank: Frequent Contributor
timestamp: September 21, 2024, 04:12:33 pm
content: Just came across this fantastic video by TI comparing reverse current blocking vs reverse polarity protection. May be helpful for other people who may come across this thread.https://www.ti.com/video/6266493685001Also the attached image that was in the video.

author: Zero999
author_rank: Super Contributor
timestamp: September 21, 2024, 04:35:36 pm
content: Quote from: ArdWar on September 14, 2024, 04:02:31 pmTrue. See simulation. The current through the battery changes direction, depending on the supply voltage. It's only good for supply reverse polarity protection.

author: madires
author_rank: Super Contributor
timestamp: September 21, 2024, 04:43:52 pm
content: As an example, the LTC4357 turns off the MOSFET when the voltage difference is more than -25 mV across the MOSFET (caused by the reverse current).