[HN Gopher] Reverse-engineering a vintage power supply chip from...
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Reverse-engineering a vintage power supply chip from die photos
Author : parsecs
Score : 83 points
Date : 2021-08-18 17:37 UTC (5 hours ago)
(HTM) web link (www.righto.com)
(TXT) w3m dump (www.righto.com)
| londons_explore wrote:
| It surprises me that even today nearly every power supply has a
| dedicated chip in like this whose task is switching a transistor
| on and off with the correct timings to regulate an output
| voltage, using mostly analogue components.
|
| It surprises me that this role hasn't been replaced with a tiny
| ARM core running some firmware to do the same. The benefit is the
| core can be self-tuning. It can detect components going out of
| spec and warn and/or compensate. It can have digital comms with
| the rest of the system to set all kinds of parameters, allowing a
| more flexible design and allowing bug fixes in the field. It can
| have lookup tables to tune efficiency for input/output voltage,
| load, etc, in a way an analogue design never could.
|
| Considering a tiny microcontroller has a BOM cost of just 4
| cents, in the same region as dedicated power supply chips, I
| don't see why software-controller-switched-mode-supplies aren't
| common.
| milankragujevic wrote:
| Too much complexity without any benefit (when adjusted for new
| failure cases and cost of additional components and
| complexity).
|
| Electronics is mostly KISS, not only motivated by the financial
| factor but also reliability, manufacturing, etc.
|
| So far micro controllers are too expensive, too sensitive to
| unstable power supply, too complex in general (requiring some
| support components in some cases, have an additional
| prefabrication step for flashing firmware by the chip vendor,
| and cost a lot more.
|
| There is no clear advantage to the approach you mentioned.
| kevin_thibedeau wrote:
| Before switching ICs became ubiquitous it _was_ common to roll
| your own with an 8-bit micro. It isn 't cost effective now
| because of the additional external components, board area, and
| NRE you'd need vs the single chip solution.
| markrages wrote:
| I was actually looking into that this week due to chip
| shortages... it is not cost effective, but if the alternative
| is sitting and waiting a year for the specialized switch
| controller to become available again, that NRE doesn't look
| too bad.
| AussieWog93 wrote:
| I've come across a broken laptop before that had a complex
| power control computer like what you've described.
|
| I ended up repairing it by hard-resetting the NVRAM and forcing
| the power control computer back to its initial "reset" state.
|
| This was a common enough problem that the manufacturer had a
| step-by-step guide showing how to fix it on their website.
|
| The moral of the story is that adding complexity, even when
| that complexity is designed to increase robustness, usually
| just means that there are more systems that can fail.
| kens wrote:
| Well, your ARM-powered chip will need some analog-to-digital
| converters since the feedback signals are analog. And you'll
| need a high-current output driver to control the switching
| transistor. And some sort of startup circuit to provide power
| before the processor starts running. And an undervoltage
| lockout circuit to prevent the processor from malfunctioning if
| the voltage drops. So you still have a bunch of analog
| circuitry but you've added an analog-to-digital converter and a
| microcontroller. There are some applications where this
| tradeoff makes sense, but in a lot of cases it would just be
| excess complexity.
| kens wrote:
| Author here if anyone has questions or comments...
| mikebco wrote:
| Have you performed any teardowns and analysis of any similar
| but newer chips? If so, how does architecture and manufacture
| compare? Have there been any significant changes in state-of-
| the-art over the last two decades?
| kens wrote:
| I've looked at more modern power supplies like a Macbook
| charger [1]. One difference is they have power factor
| correction in the frontend. Another difference is they use
| more advanced power supply topologies, such as a resonant
| converter. Also, efficiency is a bigger concern.
|
| As far as the chips themselves, I haven't looked at a modern
| power supply controller chip, but I've looked at other power
| chips [2]. The biggest difference is they are CMOS instead of
| bipolar. They are also much more complex and dense, so I
| can't reverse engineer them with my microscope.
|
| [1] https://www.righto.com/2015/11/macbook-charger-teardown-
| surp...
|
| [2] https://www.righto.com/2020/05/tiny-transformer-inside-
| decap...
| jaytaylor wrote:
| Are the physical dimensions of the chip listed somewhere in the
| article? I'm looking but haven't yet found them.
|
| At the beginning you say "this very small chip", and it would
| be cool to include the actual dimensions. This will make it
| possible to get a sense for the size of the features from the
| magnified die picture.
|
| p.s. You write some of the best articles, I love the way you
| break things down and present them in an approachable way.
| Thank you, Ken!
| kens wrote:
| I didn't take measurements, but I think the feature size is
| about 20 micrometers, which is huge compared to nanometers in
| modern chips.
| rkagerer wrote:
| Just want to say thanks for these thorough teardowns and
| wonderfully annotated die photos.
| kens wrote:
| The Visual 6502 project is what originally inspired me to
| look inside integrated circuits and see how they really work.
| Although ICs seem like mysterious black boxes, you can see
| what's going on. At least until about 1980, and then it gets
| too complicated for me :-)
|
| http://www.visual6502.org/JSSim/
| wuschel wrote:
| What are the challenges in reverse engineering more modern
| chips?
|
| PS awesome blog!
| l-albertovich wrote:
| I love your work, ever since the first time I saw one of your
| IC RE posts I felt really humbled and inspired by it so I'd
| like to take this opportunity to thank you for doing it.
|
| Thanks!!!
| ForOldHack wrote:
| Several months ago, I started reading every new article. This
| is the first comment I have left in a few weeks.
|
| Your posts are fantastic, not only do we get a peek inside,
| but we learn about how electronics work, and why designers
| make choices.
|
| Thanks!!!
| monocasa wrote:
| Would there be any benefit other than cost to analog power
| control chips like this rather than DSP controlled power
| supplies like we typically see today?
|
| I'd imagine that their better response latency is eaten up by
| downstream capacitors anyway. Maybe they'd have better dynamic
| range to allow them to converge on a clean signal better than a
| stream of digitized samples that are always probably little off
| converged one way or the other by some quantum?
|
| I'll be the first to admin that power control isn't my forte
| though, and most arguments I can come up absolutely sound like
| the specious stuff you hear out of 'audiophiles'.
| barbegal wrote:
| DSPs are more expensive to engineer than these tried and
| tested chips. If you need the functionality of a DSP then you
| use one but the core performance of a power supply is
| relatively unaffected.
| megous wrote:
| Even MCU controlled SPS often times have pure analog control
| loop, where A/D and MCU is there mostly there for monitoring
| and perhaps digital control of some loop parameters, but the
| software is not an integral part of the loop itself...
|
| Which is perhaps for the good, if you look for example on the
| boost topology, where saturation of the inductor leads to the
| shorting of the input through a switching transistor to the
| ground... :)
| pwr-electronics wrote:
| Here's an interesting video series describing such a
| software-configured, hardware-controlled switching
| controller.
|
| Here, Microchip markets this particular line of PIC MCUs as
| a "field-programmable switch-mode power controller". But
| weirdly I haven't seen that language on their main site.
|
| https://mu.microchip.com/getting-started-with-cip-hybrid-
| pow...
| kop316 wrote:
| Your blog is incredibly well done, and it is always worth my
| time (several times over) to read what you post. Thank you!
| agumonkey wrote:
| just a thanking note, for I never had the idea of inspecting
| power electronics under the hood :)
|
| do you think recent GaN power adapters have very different
| power ICs ?
| kens wrote:
| I haven't looked into GaN power adapters. I think they use
| the same control ICs but GaN transistors, but I'm not sure.
| Maybe someone else here knows more?
| pwr-electronics wrote:
| The supporting ICs are the same. For now, at least.
|
| But because of differences between GaN and Si, the
| selection of reasonably compatible controllers and gate
| drivers is smaller. For example, many ICs made for Si are
| underperformers for GaN, or they might need some
| "translation" circuitry because of different gate voltage
| requirements.
|
| There are certainly many gains to be made with GaN-specific
| supporting ICs, but that hasn't really happened yet. My
| personal threshold for acknowledging a fundamentally
| different technology would be replacing all the Si in the
| gate drive loop with GaN. The idea is to not hold back the
| GaN switch from realizing its full potential with slower
| and less efficient Si.
|
| The GaN switch itself is, of course, quite different from a
| Si power switch.
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