Re: irrational Spicing

On Wed, 30 Oct 2024 16:33:49 -0400, bitrex <user@example.net> wrote:

On 10/30/2024 4:07 PM, john larkin wrote:

Things I've seen, and even done, in Spice sims...
 
Bypassing voltage sources  (not me!)
 
Worrying about resistor power dissipation
 
Using standard parts values, like 4.7K ohms or 33nF, when the control
loop will be mostly code anyhow
 
Using +-12 or some such opamp supply voltages, and scaling signal
levels to fit. The LT Spice universal opamps will work with hundreds,
or thousands, of volt supplies.
 
Drawing hideously ugly schematics without a title, author, date, or
named nodes.
 
 
So I'm rescaling a power supply sim (I'm waiting for a run to finish
now) to have everything in actual 1:1 units. Then we will write the
control loop code to work in those same real engineering units, not
some goofy scaled integers or anything like that.
 
Keeping everything in true units as floats is ideal, but the RP2040
floating point ops are kinda slow, so we may express things as 32-bit
values, 16 bits of signed integer and 16 bits of fraction, as a sort
of fast and cheap float. But 12.5 volts is still visibly 12.5,  just
as if it were a float. That will be handy for debugging.
 
S16.16 is plenty good to express voltages and currents in a power
supply.
 

>
>
Floating point kind of sucks for low frequency systems with relatively
long time constants, anyway. There are applications that need 1800 dB of
dynamic range, audio isn't really one of them

What has that much dynamic range?

Most real systems, especially my power supply, will have lots of free
noise dithering. That makes the variables have essentially infinite
resolution.