Re: dc/dc soft start

On Wed, 22 Jan 2025 22:47:10 +0100, Klaus Kragelund
<klauskvik@hotmail.com> wrote:

On 21-01-2025 01:18, john larkin wrote:

On Mon, 20 Jan 2025 22:09:05 +0100, Klaus Kragelund
<klauskvik@hotmail.com> wrote:
 

On 16-01-2025 01:12, john larkin wrote:

>
Here's my soft start circuit. Thanks for suggestions from Tilmann and
Jeroen.
>
The idea is to drive the ends of the transformer with in-phase square
waves and then slowly walk them to 180 degrees, to achieve a soft
start. An FPGA can do that easily. We might take a second... but that
would simulate forever.
>
What works well is to use two spice "modulator" elements and FM the
frequency of one of them for 50 ms, until they are 180 degrees out of
phase.
>
Spice BV elements with sin(time*freq) type expressions seemed to
overload or something.
>
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>
Very nice simulation
>
I did a digital SMPS +10 years ago, use the same softstart principle.
Was based on a halfbridge converter, so if it did not have softstart
inrush current was very large. I believe you can do the same with phase
shifted controllers, but they are probably very expensive. I did it with
a 30cent microcontroller.

 
Envision an FPGA. Spin up a 200 MHz clock and stick that into a 10 bit
binary counter. The MSB is a 200 KHz square wave that drives one
half-bridge.
 
Now stick that into a 10-bit adder, add integer P to it. The sum is
the counter phase shifted by P, so the MSB is similarly time shifted,
driving the other half bridge. Start it all up and tick P up to 512 at
the power supply ramp-up rate, maybe over a second.
 

Yeah, the idea is nice.
>
But I not that much of a fan of FPGAs. Very expensive compared to
microcontrollers. In some applications they are trusted more than Class
B embedded SW, and have more performance than microcontrollers. But for
the price of that FPGA, you can probably buy 100 cortex microcontrollers.

We have a modular power system with plugin boards, and every board has
an FPGA, so the function is incrementally free. The FPGA is an Efinix
T20, about $10.

Here's the system:

https://highlandtechnology.com/Category/MPS

We really need an FPGA on these boards. There are three 50 MBPS data
streams to and from the motherboard, and fast PWM generation and
stuff.

I'm designing a 4-channel dummy load board that simulates programmable
resistance+inductance, like a solenoid or something. It needs four
isolated power supplies.