Path: ...!Xl.tags.giganews.com!local-3.nntp.ord.giganews.com!news.giganews.com.POSTED!not-for-mail NNTP-Posting-Date: Tue, 01 Oct 2024 21:57:35 +0000 From: Joe Gwinn Newsgroups: sci.electronics.design Subject: Re: power supply discharge Date: Tue, 01 Oct 2024 17:57:35 -0400 Message-ID: <9rrofjl740uqa802t624mdonu60bdb23k2@4ax.com> References: <4nrifjdkjuhai9dujuhir4eu91alovqjf6@4ax.com> <7i6lfjh7m3bt17jn2ponboi0a2refvpuob@4ax.com> <01lmfj52p9aurg23v6oq29j3shutja5tnb@4ax.com> <6baofjtquh870j7ccl49q9lc1lalcgmedv@4ax.com> User-Agent: ForteAgent/8.00.32.1272 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 120 X-Usenet-Provider: http://www.giganews.com X-Trace: sv3-BRjxa1YdfanM1piOEh+HYeyp/3cPUNPD1UtS1GjX02ecLGxeTBvM7sxOwybGfDFGtnniuI96VdLHlyY!sLJiEKxJpHoreNy51my8nWTNN78Gu1MRmyr5DGjxmh9pwGbezyuWfto6dLfWw34AuuDkBY8= X-Complaints-To: abuse@giganews.com X-DMCA-Notifications: http://www.giganews.com/info/dmca.html X-Abuse-and-DMCA-Info: Please be sure to forward a copy of ALL headers X-Abuse-and-DMCA-Info: Otherwise we will be unable to process your complaint properly X-Postfilter: 1.3.40 Bytes: 6432 On Tue, 01 Oct 2024 14:00:50 -0700, john larkin wrote: >On Tue, 01 Oct 2024 16:03:40 -0400, Joe Gwinn >wrote: > >>On Tue, 01 Oct 2024 09:59:27 -0700, john larkin >>wrote: >> >>>On Tue, 01 Oct 2024 11:24:34 -0400, Joe Gwinn >>>wrote: >>> >>>>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 >>> >>>Makes sense. It looks like most MOV appnotes assume that it's across >>>an AC line, with kilo-amps available. Or lightning bolts. >>> >>>I'll get a few and test them at much lower loads. >> >>For smaller MOVs, I think that the data sheet specifies capacity in >>Joules. I bet this is the max integrated dose, not the pre-event >>limit. Well, the one-event limit as well. >> >>Joe Gwinn > >That's probably a single-shot rating, such as to limit the peak >temperature. So that can be done many times, if it cools off between >shots. In traditional MOVs, I think that there are two limits, max single pulse and integral of all pulses to date, with some variations as to pulse width. I have these in my house, in the AC power panel. For the Delta Lightning Silicon Oxide limiters, they don't seem to wear out all that fast, or at all. Maybe time to replace those old arrestors in the power panel. Joe Gwinn