Path: ...!weretis.net!feeder6.news.weretis.net!feeder8.news.weretis.net!fu-berlin.de!uni-berlin.de!individual.net!not-for-mail From: liz@poppyrecords.invalid.invalid (Liz Tuddenham) Newsgroups: sci.electronics.design Subject: Re: power supply idea Date: Mon, 22 Apr 2024 17:30:40 +0100 Organization: Poppy Records Lines: 45 Message-ID: <1qsff6o.1wpvmay7c6tqoN%liz@poppyrecords.invalid.invalid> References: <1qsex7l.10jlqkcsogkxsN%liz@poppyrecords.invalid.invalid> X-Trace: individual.net xjlo1QtiMrDbkuRBItRo/ADRLvz42axlWS33txE4CUZHsxYMTj X-Orig-Path: liz Cancel-Lock: sha1:F+DpGUD1KV2JT4veTBVWENBWxls= sha256:ebnpq4MaZWrmbp1LIeQ7xoNuuqr1lfRaLvn1wFQvD0k= User-Agent: MacSOUP/2.4.6 Bytes: 2910 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. -- ~ Liz Tuddenham ~ (Remove the ".invalid"s and add ".co.uk" to reply) www.poppyrecords.co.uk