24V-300V, 1000W DC-DC Push-pull simulation with precharge 90% efficient

[Joerg]

"legg" wrote in message
- but didn't do the 'work' for him. 'fait accomplis' tends to sell.
The whole simulation business gives me the squitters, when no
hardware is being built. It takes effort to make a simulation
represent real hardware, even after it's built.
Only really useful to demonstrate basic priciples or to predict
iterations of subcircuits - and even then you need to add salt.
Well, in this case I actually have built the hardware, and it worked for
a while but suffered from certain problems such as high voltage spikes
and extreme current surges. So with the help of some more experienced
people here, I was able to see where my design had issues, and now after
another round of simulation, I think I am ready to rebuild the hardware
and try again.

There are some things that do not lend themselves well to simulation. I
plan to use a PIC, probably the PIC16F684 or PIC16F616, but their PWM
modules are not suited to a push-pull topology except at 50% duty cycle.

And that's exactly where the main problems is. Every mundane switcher IC
worth its salt has a soft-start feature. Other than a little ceramic cap
it requires zero in additional parts.

I don't know what it is with these PICs. They are ok as a uC but why are
people using them as switcher chips? It makes no sense. I've seen
designs where they were used (against my advice) and very painful
compromises resulted. These things cannot do proper current mode
control, there is no good dead time control, there is no easy soft-start
solution, any loop that was being attempted was bog-slow, and to top it
all off the uC cost a lot more than a switcher chip that could have done
a much better job.

[...]

The one time I considered it (with an AVR) the AVR was for something
else. And it was hey, look, I can take this bit away, and that bit, and
do this in software, and even the power supply chip could go if i wanted.

For a tiny helper supply, no objections. But what Paul is doing is a
very serious switcher something that most definitely is not a home run
for a micro controller.

 

[[email protected]]

[...]

I don't know what it is with these PICs. They are ok as a uC but why are
people using them as switcher chips? It makes no sense. I've seen
designs where they were used (against my advice) and very painful
compromises resulted. These things cannot do proper current mode
control, there is no good dead time control, there is no easy soft-start
solution, any loop that was being attempted was bog-slow, and to top it
all off the uC cost a lot more than a switcher chip that could have done
a much better job.

To show that they can? Playtime? First do no harm.

But micro controllers can't. That's the problem. Unless you have a
nearly infinite horsepower in the thing which will results in high cost,
a fat chip and wasteful power consumption.

But it works, sorta, and shows how smart they are (the real reason).

 

[Joerg]

But it works, sorta, and shows how smart they are (the real reason).

Nah, I believe most engineers do that so they have the utmost
flexibility. Which I do understand, it's just that in nearly all
switcher cases that's really not a good strategy.

My main gripe is slow loops. Then you end up with bigger inductors and
bigger caps. This leads to blowing size constraints and it also
increases the BOM cost substantially. The worst case is when the
slowpoke-uC solution becomes the reason to "need" electrolytics because
then the MTBF takes a nosedive.

 

[Fred Abse]

I don't know what it is with these PICs. They are ok as a uC but why are
people using them as switcher chips?

Because they're code scribblers, not engineers.

 

[Joerg]

Because they're code scribblers, not engineers.

But Paul comes across like a real engineer. One that does not even shy
away from using a big angle grinder and a welder.

 

[Fred Abse]

But Paul comes across like a real engineer. One that does not even shy
away from using a big angle grinder and a welder.

So he does. I'd have thought he wasn't the PIC type. More of a discrete
component guy.

;-)

 

[P E Schoen]

"Fred Abse" wrote in message

So he does. I'd have thought he wasn't the PIC type. More of a discrete
component guy.

I've always tried to find the best tools for the job, and I prefer having
the flexibility of programmable components, such as PICs. My unique niche
involves instrumentation that may need to handle low level signals, and
connectivity to PCs and the software for that, but also high power devices
running off 480V 200A mains and producing currents up to 100,000 amps. And I
also get to design mechanical components such as heavy steel cabinets on
800lb castors, machined copper and phenolic pieces, motor drives, and
panels. More recently, mostly as a hobby, I have been investigating EVs,
including personal railways, hybrid car kits, electric tractors, and
full-size electric cars, trucks, and RVs.

I tend to think "outside the box" and investigate various ways to achieve
the same end result. I prefer "hands on" design which sometimes uses the
"shotgun" approach of trying something just for the hell of it to see how it
plays, mostly using the less dramatic simulator approach rather than actual
hardware, but that too. I probably should be more methodical and calculate
the parameters of the components and the circuit topology, but I also like
to explore possibilities using a "what if" approach.

The reasons for using PICs include their versatility and low cost, but also
the fact that I like programming them. In fact, even as far back as 1969, I
realized that I was better at computers and lab work than I was at pure EE,
and I changed my major accordingly. But for a long time thereafter I worked
at consumer electronics repair, and instrument calibration, before I segued
into electronics design engineering around 1977.

I also enjoy working with power tools and large machinery and I've done my
share of automotive repair and I even had a bulldozer for a while. And I
have also pursued other interests such as hiking, volleyball, singles clubs,
intentional community, guitar, dog behavior, cosmology, quantum mechanics,
organic gardening, psychology, philosophy, cooking, and animal rescue. It's
a very interesting world, and I have a fairly good idea of how mechanical
and electrical things work, but people have always been an enigma that can
be fascinating as well as depressing. I think technology can be part of our
hope for a bright future, but I think we must learn from nature and animals
and "less advanced" civilizations about how to get along with each other and
avoid decimating our environment.

Thanks,

Paul

 

[[email protected]]

[email protected] wrote:
[...]

I don't know what it is with these PICs. They are ok as a uC but why are
people using them as switcher chips? It makes no sense. I've seen
designs where they were used (against my advice) and very painful
compromises resulted. These things cannot do proper current mode
control, there is no good dead time control, there is no easy soft-start
solution, any loop that was being attempted was bog-slow, and to top it
all off the uC cost a lot more than a switcher chip that could have done
a much better job.
To show that they can? Playtime? First do no harm.

But micro controllers can't. That's the problem. Unless you have a
nearly infinite horsepower in the thing which will results in high cost,
a fat chip and wasteful power consumption.

But it works, sorta, and shows how smart they are (the real reason).

Nah, I believe most engineers do that so they have the utmost
flexibility. Which I do understand, it's just that in nearly all
switcher cases that's really not a good strategy.

Ah, hell, if you want it fast and flexible, and still prove you're
UberEngineer, just use an FPGA. ;-)

My main gripe is slow loops. Then you end up with bigger inductors and
bigger caps. This leads to blowing size constraints and it also
increases the BOM cost substantially. The worst case is when the
slowpoke-uC solution becomes the reason to "need" electrolytics because
then the MTBF takes a nosedive.

SMPS chips aren't free or zero MTBF, either, OTOH, interrupts or a system
reset won't cause smoke, either. Verification is just too much of a problem
to even consider this insanity.

 

[Chieftain of the Carpet Crawlers]

Looks better on a resume.

RL

Our piezo stack driver was full audio range, and went from about 24V up
to about 900V

It had a whole row of IGBTs on it, all wired real close to the board,
stuffed with ferrite beads and a big, long extrusion for the heat sink.
It was 900V at half an amp.

The thing had two 2kVa transformers in the bottom of the case.

 

[Chieftain of the Carpet Crawlers]

So he does. I'd have thought he wasn't the PIC type. More of a discrete
component guy.

;-)

PIC'n and a grinin'...

 

[Jamie]

Our piezo stack driver was full audio range, and went from about 24V up
to about 900V

It had a whole row of IGBTs on it, all wired real close to the board,
stuffed with ferrite beads and a big, long extrusion for the heat sink.
It was 900V at half an amp.

The thing had two 2kVa transformers in the bottom of the case.

sounds inefficient.

Jamie