Path: ...!weretis.net!feeder8.news.weretis.net!reader5.news.weretis.net!news.solani.org!.POSTED!not-for-mail From: Jan Panteltje Newsgroups: sci.electronics.design Subject: Re: power supply discharge Date: Wed, 02 Oct 2024 06:17:31 GMT Message-ID: References: <4nrifjdkjuhai9dujuhir4eu91alovqjf6@4ax.com> <7i6lfjh7m3bt17jn2ponboi0a2refvpuob@4ax.com> <01lmfj52p9aurg23v6oq29j3shutja5tnb@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; ISO-8859-15 Content-Transfer-Encoding: 8bit Injection-Date: Wed, 2 Oct 2024 06:17:32 -0000 (UTC) Injection-Info: solani.org; logging-data="1088271"; mail-complaints-to="abuse@news.solani.org" User-Agent: NewsFleX-1.5.7.5 (Linux-5.15.32-v7l+) Cancel-Lock: sha1:G4OOqmddbkNUSkZU4L22o6u9rWY= X-User-ID: eJwNycEBwCAIA8CVoCGo41AJ+4/Q3veI9LwrkhkczurrBYM9ZmLO3157jrZKebxFus8KMLfcqvk2HsmjBeADQFQVIA== X-Newsreader-location: NewsFleX-1.5.7.5 (c) 'LIGHTSPEED' off line news reader for the Linux platform NewsFleX homepage: http://www.panteltje.nl/panteltje/newsflex/ and ftp download ftp://sunsite.unc.edu/pub/linux/system/news/readers/ Bytes: 5143 Lines: 90 On a sunny day (Tue, 01 Oct 2024 11:24:34 -0400) it happened Joe Gwinn wrote in : >On Mon, 30 Sep 2024 18:49:14 -0700, john larkin wrote: > >>On Mon, 30 Sep 2024 11:49:54 -0700, Joerg >>wrote: >> >>>On 9/30/24 11:24 AM, john larkin wrote: >>>> On Mon, 30 Sep 2024 08:39:27 -0400, legg wrote: >>>> >>>>> On Sun, 29 Sep 2024 08:23:01 -0700, john larkin wrote: >>>>> >>>>>> On Sat, 28 Sep 2024 22:28:07 -0700, Joerg >>>>>> wrote: >>>>>> >>>>>>> On 9/27/24 8:07 AM, john larkin wrote: >>>>>>>> >>>>>>>> Given a benchtop power supply, you can turn the voltage up and then >>>>>>>> down, and it goes down. Most have a substantial amount of output >>>>>>>> capacitance, and can be driving an external cap too. So something >>>>>>>> pulls the output down. >>>>>>>> >>>>>>> >>>>>>> Often the only internal load is the resistive divider for the regulator >>>>>>> loop feedback. >>>>>>> >>>>>>> >>>>>>>> I guess that there are no standards for this, but I've never seen a >>>>>>>> supply that just hangs high when it's cranked down. >>>>>>>> >>>>>>> >>>>>>> I have some. They drop very slowly when there isn't much load on the output. >>>>>> >>>>>> Customers might whine if they ask for 10 volts and see 30. Amd that >>>>>> may be mostly held up by their capacitive load. >>>>>> >>>>>>> >>>>>>> >>>>>>>> I'm designing some programmable multi-channel power suplies and that >>>>>>>> is one of many tangled issues in the project. >>>>>>>> >>>>>>> >>>>>>> A synchronous buck architecture should work quite well if you need to >>>>>>> slew fast. I've used that on a driver that had to modulate a hard >>>>>>> capacitive load at several kHz and above 100V. >>>>>> >>>>>> I'm doing some multichannel non-isolated supplies that will be sync >>>>>> buck, using multiple TI DRV8962 chips. >>>>>> >>>>>> One problem is that a sync buck can become a boost in the wrong >>>>>> direction, and start charging my +48 supply. If it hits, say, 55 >>>>>> volts, I'll disable the switcher chips, and the outputs can hang. I >>>>>> need to discharge the outputs. I'm thinking about 20 mA of depletion >>>>>> fet per channel. >>>>> >>>>> You might consider overvoltage protection or a (switched ?) >>>>> internal minimum load.There's usuaally some point in the >>>>> control loop that's a good indicator of a pull-down requirement. >>>>> A single ovp or autoload on the input looks likely to serve >>>>> all of your many sync-bucks. >>>>> >>>>> RL >>>> >>>> An MOV on the bulk supply could limit the reverse-pump excursion until >>>> the software can notice and shut things down. >>>> >>>> MOVs can gobble a lot of joules, but their clipping is very soggy. >>>> >>> >>>MOVs are usually cumulative. They can take a certain amount of >>>dissipation over their lifetime and then *PHUT* ... POOOF. Like a bank >>>account that runs dry. >> >>What kills MOVs? Integrated joules? Time-temperature? >> >>I don't expect a lot of joules per event. Just enough energy to keep >>my supply voltage down until a slowish ADC and the software can shut >>the buck switchers down. 15 milliseconds max, maybe. > >I think it's integrated joules per cubic centimeter of the MOV >material. This is discussed in the literature on MOVs for protecting >line-powered equipment from pulse overvoltages, such as from nearby >lightning strikes. > >Joe Gwinn Protects my washer: https://panteltje.nl/pub/mains_protector_IXIMG_0501.JPG https://panteltje.nl/pub/main_protector_IXIMG_0503.JPG VDRs with spark gaps.