Path: ...!weretis.net!feeder8.news.weretis.net!eternal-september.org!feeder3.eternal-september.org!news.eternal-september.org!.POSTED!not-for-mail From: Klaus Vestergaard Kragelund Newsgroups: sci.electronics.design Subject: Re: power supply idea Date: Wed, 24 Apr 2024 01:52:51 +0200 Organization: A noiseless patient Spider Lines: 88 Message-ID: References: <20240422b@crcomp.net> <2ufg2jhb1tdii3u2psckrel51s4de350ic@4ax.com> MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Injection-Date: Wed, 24 Apr 2024 01:52:51 +0200 (CEST) Injection-Info: dont-email.me; posting-host="ef5ae58932111e467ea3049749f7379f"; logging-data="2018735"; mail-complaints-to="abuse@eternal-september.org"; posting-account="U2FsdGVkX196UeJ3AbpgpRi4jrr90kvIKfgBe6z6pC4=" User-Agent: Mozilla Thunderbird Cancel-Lock: sha1:sU1uM+VLfZcKjFqCN5QApEFekZU= In-Reply-To: <2ufg2jhb1tdii3u2psckrel51s4de350ic@4ax.com> Content-Language: en-US Bytes: 5388 On 24-04-2024 01:17, john larkin wrote: > On Tue, 23 Apr 2024 23:56:44 +0200, Klaus Vestergaard Kragelund > wrote: > >> On 23-04-2024 23:47, Klaus Vestergaard Kragelund wrote: >>> On 22-04-2024 20:09, John Larkin wrote: >>>> On Mon, 22 Apr 2024 17:38:19 -0000 (UTC), "Don" wrote: >>>> >>>>> John Larkin wrote: >>>>>> erichpwagner 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. >>>>>>>> >>>>>>>> We can constrain the influence range of the integrator, just >>>>>>>> enough to >>>>>>>> give the regulation that we need. That limits output swing in case >>>>>>>> the >>>>>>>> feedback is wrong, as one could get from a botched remote sense >>>>>>>> connection. >>>>>>>> >>>>>>>> https://www.dropbox.com/scl/fi/2fysyvkl4eim7vujhaobh/FFINT_PS_1.jpg?rlkey=rug6yi3cgemi9vvbz8apgboqi&raw=1 >>>>>>> >>>>>>> Looks like you have invented the buck converter. >>>>>> >>>>>> I invented a control algorithm. All the buck chips that I know of are >>>>>> all feedback driven, and will slam into either rail if the feedback >>>>>> divider is broken. Blow things up. >>>>> >>>>> An algorithm arguably eliminates a 555 triangle generator as a potential >>>>> spread spectrum source. LOL. So, what's hidden in plain sight behind all >>>>> of your left hand side, symbolic sleight of hand? In other words, how do >>>>> you implement your control algorithm? >>>>> >>>>> Danke, >>>> >>>> It's all in plain sight. Well, the guts of the PWM converter isn't, >>>> but that's pretty obvious. >>>> >>>> The PWM converter, and in fact everything, will be implemented in an >>>> FPGA, with an ADC to pick up the output voltage. >>>> >>>> May as well go pseudo-random on the spread spectrum part. Any audible >>>> side effects would be hiss, not whine. >>>> >>> >>> I have done what you propose, but I did not add the spread-spectrum part. >>> >>> If you add a current sense on the output, you can characterize the >>> non-linearity of the power stage, and do feedforward compensation. So >>> your response will be snappy. You still have the settle time of the LC >>> filter, that's harder to counteract with feedforward. >>> >> One concept I never had time to implement, was to do in circuit >> compensation. So in your function test, add a swept current load on the >> output at different output voltages, and feed the results to the >> feedforward lookup table. That will take care of variations on >> components, albeit wont reduce temperature affected errors. > > One of our applications has a fixed, stiff 48 volt supply. So we > could characterize the switcher output as an ohmic source, and use the > sensed current to null out most or all of those ohms, so the > integrator can have an even smaller influence range. Or even no > integrator! We need a current sensor anyhow. > Sounds like a fun project. You could do this with a 0.3 USD ARM CM0 processor, but I guess you have the FPGA on the board anyhow. > Another product will have an isolated dc/dc converter driving the > half-bridge, and it will be fairly soft, nonlinear at that. We will > digitize that 60 volt supply anyhow, so it and the current together > could be compensated. That might require a divide in the FPGA. I'll > ask my FPGA kids if they can divide. >