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From: john larkin <jl@650pot.com>
Newsgroups: sci.electronics.design
Subject: Re: power supply idea
Date: Tue, 23 Apr 2024 16:17:15 -0700
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On Tue, 23 Apr 2024 23:56:44 +0200, Klaus Vestergaard Kragelund
<klauskvik@hotmail.com> 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" <g@crcomp.net> 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.

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.