Warning: mysqli::__construct(): (HY000/1203): User howardkn already has more than 'max_user_connections' active connections in D:\Inetpub\vhosts\howardknight.net\al.howardknight.net\includes\artfuncs.php on line 21
Failed to connect to MySQL: (1203) User howardkn already has more than 'max_user_connections' active connectionsPath: ...!news.mixmin.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: legg Newsgroups: sci.electronics.design Subject: Re: power supply discharge Date: Mon, 30 Sep 2024 08:39:27 -0400 Organization: A noiseless patient Spider Lines: 52 Message-ID: <7i6lfjh7m3bt17jn2ponboi0a2refvpuob@4ax.com> References: <4nrifjdkjuhai9dujuhir4eu91alovqjf6@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Injection-Date: Mon, 30 Sep 2024 14:37:23 +0200 (CEST) Injection-Info: dont-email.me; posting-host="aae8c7d41363bf09d1d51f5ed78562c7"; logging-data="2365867"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX1+0Ba8WIE872AWiC+rbLWrC" Cancel-Lock: sha1:pb7W78jAW9mHcUIfuMYe7GqtCDI= X-Newsreader: Forte Agent 4.2/32.1118 Bytes: 2954 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