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From: Lasse Langwadt <llc@fonz.dk>
Newsgroups: sci.electronics.design
Subject: Re: power supply idea
Date: Wed, 24 Apr 2024 21:16:19 +0200
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On 4/24/24 01:17, john larkin wrote:
> 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.
> 

division is just like any other operation, it just takes more cycles 
since since it can't be done in parallel like a multiply