Path: Xl.tags.giganews.com!local-2.nntp.ord.giganews.com!nntp.supernews.com!news.supernews.com.POSTED!not-for-mail NNTP-Posting-Date: Mon, 22 Apr 2024 19:17:55 +0000 From: John Larkin Newsgroups: sci.electronics.design Subject: Re: power supply idea Date: Mon, 22 Apr 2024 12:16:07 -0700 Organization: Highland Tech Reply-To: xx@yy.com Message-ID: References: <1qsex7l.10jlqkcsogkxsN%liz@poppyrecords.invalid.invalid> <1qsff6o.1wpvmay7c6tqoN%liz@poppyrecords.invalid.invalid> X-Newsreader: Forte Agent 3.1/32.783 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Lines: 51 X-Trace: sv3-v3OxBR9tkOJotcOXE79v0/QH8mpvRPSOSP/iKHC3fdBL+gZ3JHMEw0gLPdRLpY1bkKE4sigOdOxmV4C!hDFKvkaFuCTKdMYlcYIE9Ot9m+jvAu2Q6uBSfW8dqCLN+Q+tp11KSMWE78p6E5Bu+yvLV37Hxcpp!JGa6bA== X-Complaints-To: www.supernews.com/docs/abuse.html X-DMCA-Complaints-To: www.supernews.com/docs/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: 3658 On Mon, 22 Apr 2024 17:30:40 +0100, liz@poppyrecords.invalid.invalid (Liz Tuddenham) wrote: >John Larkin wrote: > >> On Mon, 22 Apr 2024 11:10:41 +0100, liz@poppyrecords.invalid.invalid >> (Liz Tuddenham) wrote: >> >> >John Larkin wrote: >> > >> >> If one had, say, a 48 volt power bus, you could hang a half-bridge >> >> switcher to ground, and a lowpass filter out. If the drive has duty >> >> cycle n, the output voltage is 48*n. So we have a programmable power >> >> supply with no feedback, which will be stable into any load. >> >> >> >> The load regulation will be mediocre, but we could almost sell it >> >> as-is. >> >> >> >> So now, sense the output voltage and compute the error against the >> >> target, run through a slowish integrator, and tweak the PWM to get >> >> zero output voltage error. Gross transient response is basically the >> >> response of the output filter, with some modest drool from the >> >> integrator. >> > >> >In thory, pulse-width contol of the output could give excellent >> >stability under load -- but the filter is going to cause droop. Unless >> >you are very careful about the design of the filter, the phase shifts it >> >creates will make the feedback loop unstable. An integrator in the loop >> >will stabilise this at the expense of a much slower response time. >> > >> >Somewhere in the loop you need a dominant pole so that (to use audio >> >amplifier terminology) your roll-off is 6dB per octave until the loop >> >gain has dropped far enough for stability when all the other phase >> >shifts kick in and the slope increases to 12dB per octave or more. >> >Rather than integrating the feedback, transferring the dominant pole to >> >the filter will result in less output noise and a faster response to a >> >step increase in the load. >> >> An LC filter is at least 2-pole, usually more, > >If you made it three poles, with one of them significantly lower >frequency than the other two, stability would be much easier to obtain. Capacitor ESR, native or added, helps. I also want to kill the Q as seen from the load side, so it doesn't ring much if they switch an inductive load. The load-from-hell is of course some box with a switching regulator power supply, that looks like a negative resistance load.