Digital SMPS controller - Page 1
Forum section: electronics / projects

author: blueskull
author_rank: Unknown
timestamp: April 01, 2017, 08:19:23 am
content: Hi all. Is there a recommendation on which digital SMPS controller to use for a hobby project?The needs are listed:1. PWM controls for 2 half bridges, one for totem-pole bridge-less PFC, the other for a half bridge converter. Both operate at fixed frequency, both shall support pulse skipping, forced CCM only. PFC switches at 150kHz~250kHz, half bridge converter operates at 500kHz fixed. Totally 2 pairs of complementary PWM outputs needed. Delay line based 1ns resolution needed, timer-only based PWM is not an option.2. 12bit+ ADC, sampling at at least 1Msps, multiple channels interleaved for PFC voltage feedback, PFC current feedback, AC voltage sensing, and isolated output voltage sensing (maybe isolated sigma delta converter or conventional TL431+optocoupler).3. CPU power to process ADC data, PFC operates in average current mode as inner control loop, and voltage mode in outer control loop, half bridge converter operates in voltage mode. All compensators for 3 loops are presumably 2P2Z. Control loops update at at least 100kHz including interrupting overheads.4. Physically, as low power as possible, as small as possible, must be in a lead-less packaging such as QFN/DFN/BGA/CSP.5. A debugging UART interface is preferred, watchdog is a must, others digital peripherals besides PWM are not necessary. Flash should be enough for some basic control code and printf/scanf without floating number support.Here are few candidates I already know:1. TI UCD3028 in 6*6 QFN36 package, hardware digital 3P3Z control, no PFC capability, but can be added by controlling outer loop with CPU and using DAC to drive reference of inner loop. 6-bit narrow range 1mV resolution error ADC, 250ps PWM, free IDE.2. TI F28035 in 7*7 QFN56 package, software control only, with CLA and DSP cores both running at 60MHz, 3.5Msps 12-bit ADC, 300ps PWM, free IDE.3. Microchip dsPIC33EP16GS202 in 4*4 QFN28 package, software control only, 16-bit dsPIC core running at 60MHz (actually 70, but 60 is over entire temp range), 3.25Msps 12-bit ADC, low power consumption (compared with previous two), 1ns PWM, $995 compiler PRO license.Both should be able to do the job, but I prefer the third for its small size and low power consumption, also its ICSP is easier to use compared to the others'. However, the $995 cost is something I don't want to spend. I can get started by using the free license, and only switch to pro license afterwards. Personally I don't have experience with ARM7, nor any UCD chips, so I would say it might need some learning curve. I work with Delfino DSPs extensively at work, so switching to Piccolo should be easy. I've never worked with dsPIC either, but I did work with 8-bit PIC, if that matters.Any ideas are welcomed.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 01, 2017, 11:22:46 am
content: Try ST for everything including Mosfet and Diodes, I suggest you maybe able to decrease loop frequency to be able to do it with only a few 0.5USD cortex M0 from ST (STM32F030K6T6) , I'm designing something similar with a 0.5USD ST MCU for each part. a separate one for example for PFC control only, in this way you are true "multie-core" with insanely easy and cheap way of doing it!

author: technix
author_rank: Super Contributor
timestamp: April 01, 2017, 01:23:37 pm
content: STC15W401AS + TL431 external reference. 35MHz 1T 8051 core. Does everything (except the 10-bit ADC.) Super cheap (less than $1 total.)

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: April 01, 2017, 03:01:58 pm
content: QuoteSTM32F030K6T6 is 48MHz and have :)1MSPS ADC and it's 32bit and it's 0.5USD

author: coppice
author_rank: Super Contributor
timestamp: April 01, 2017, 03:43:55 pm
content: Quote from: blueskull on April 01, 2017, 08:19:23 amI don't think anything matches the C2000 family for digital power supplies, but the 38035 is not the best part for that job. Its a while since I looked through the range, so I can't remember the right part numbers, but there are parts battled hardened for power supply applications, with the bells and whistles needed to kept external circuitry to a minimum.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 01, 2017, 04:38:01 pm
content: I am about 1/3 of the way through a C2000 based project. Honestly I did not exhaust every possible option, but the C2000 jumped out early for all the reasons mentioned above. I doubt I will push it to the limits on my first try, but from what I have learned so far - its a seriously capable feature set.Sent from my horrible mobile....

author: JPortici
author_rank: Super Contributor
timestamp: April 01, 2017, 04:39:58 pm
content: i used that dspic, a very nice one! be careful though, read the errata. if memory serves right the shared ADC core has some issues (i only used core 1 2 and 3 so it didn't affect me) and interleaved mode has issues too. this has the same issues the ADC in pic32mz has (i think it's the same IP)usually the ADC in dspics is very accuratethere is no need for compiler pro licence. it's GCC based, O1 can be enabled in "free" mode, it removes almost all the bloat and if you want you can recompile from sources and remove the licensing bit.if you need i can share some code to set up the ADC, it's not really easy (compared to other PICs)

author: znroot
author_rank: Contributor
timestamp: April 01, 2017, 05:20:01 pm
content: I would reccomend to you the TI's DSP TI F28035 because it is designed also to do smps controller. I used it in my fully-digital control of a full-bridge inverter (3.3KW output power) and it works very well.It has also a nice feature called HREPWM which, thanks to a edge-positioning trigger signal, can improve your bit resolution by 3-4 bit maintaining the same CPU clock.Anyway the CLA (+FPU) included into is very useful for a digital controller saving you many hours of headache caused by fixed point math

author: BravoV
author_rank: Super Contributor
timestamp: April 01, 2017, 06:38:30 pm
content: Quote from: blueskull on April 01, 2017, 08:19:23 amAs others suggested on C2000, and also looking at few highlighted items above, have you take a glance on C2000's guts like these for examples ? .... cause sometimes the devil is in the details.Pwm capabilities :• Achieve unprecedented precision with unparalleled high resolution duty-cycle control down to55ps time steps• Reduce power-switching loses with high-resolution and configurable deadband support• Protect your system and add safety features with direct PWM tripping from comparator or trip zone pin inputs•Flexible PWM outputs configurations, including dual-edgeasymmetric and symmetric PWM generation• Programmable or hardware-locked PWM time and phase synchronization

author: rx8pilot
author_rank: Super Contributor
timestamp: April 02, 2017, 03:43:55 am
content: My project is also using eGaN Fets as well. Interesting challenges with those devices and I quickly discovered that custom digital control is the best way to take advantage of their characteristics. I got a great book from EPC that was helpfulhttp://epc-co.com/epc/Products/Publications.aspx

author: rx8pilot
author_rank: Super Contributor
timestamp: April 02, 2017, 05:12:08 am
content: Quote from: blueskull on April 02, 2017, 04:17:12 amHire me. I work hard!

author: BravoV
author_rank: Super Contributor
timestamp: April 02, 2017, 05:20:10 am
content: Keep us posted on this cool smps will ya.

author: jbb
author_rank: Super Contributor
timestamp: April 02, 2017, 07:01:32 am
content: Quote from: blueskull on April 02, 2017, 04:17:12 amDo Microchip offer an academic license? That might solve your $995 compiler problem.

author: JPortici
author_rank: Super Contributor
timestamp: April 02, 2017, 08:19:03 am
content: More info:https://www.eevblog.com/forum/microcontrollers/is-microchip-violating-the-gpl/msg1009052/#msg1009052

author: coppice
author_rank: Super Contributor
timestamp: April 04, 2017, 09:20:22 am
content: Quote from: blueskull on April 04, 2017, 08:37:10 amWhich dsPIC33 are you looking at? Power consumption, for real applications scenarios, usually favours the C2000.

author: BravoV
author_rank: Super Contributor
timestamp: April 04, 2017, 09:28:57 am
content: Quote from: blueskull on April 04, 2017, 08:37:10 amCurious how much power that TI chip consumes compared to dsPIC33 ? Which TI chip is that ?

author: JPortici
author_rank: Super Contributor
timestamp: April 04, 2017, 04:44:33 pm
content: I use extensively the dsPIC33EV family and i can confirm blueskull's numbers for it.in a current prototype with dspic33EV and 25AC eeprom, with the eeprom idle i get about 16mA at room temperature-5V-16 MIPS-peripherals enabled: 2xSENT 3xTIMER 2xOC 1xI2C 1xUART.scaling it for his scenario (3V3, increased speed, all peripherals on) 20 mA are believable at room temp.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 04, 2017, 05:03:12 pm
content: Quote from: blueskull on April 04, 2017, 04:16:22 pmAs long as the GS202 has the performance to take full advantage of your design. I don't know anything about that chip, but it is worth looking at the architectural details to see if you gain .2% 'for free' while some other limitation of the architecture is costing you .5%.

author: insine
author_rank: Contributor
timestamp: April 04, 2017, 06:03:43 pm
content: You may also consider STM32F334.It is 72MHz ARM Cortex M4 with FPU, 217ps resolution PWMs and 5MSps 12 bit ADCs.Seems quite nice, but no QFN packages though.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 04, 2017, 07:10:21 pm
content: Novel/Experimental evm designs seems to be in the marketing circles (also to push the sales agenda), I have some serious concerns about the practicality of a fully "Digital SMPS Design" in the real world (of which few actually exists)1) Control logic Voltage and Current loops are essentiallyreal-time code.2) With the above said, debugging is extremely tricky, so much potential to destroy the output stage or seriously damage the power stage with software breakpoints latching critical control signals or creating erratic timing issues.3) Debugging, designing even a simple Type-II compensator is over kill using signal processing code, it takes alot of of CPU resources to execute real-time signal processing calculations and well tested robust algorithms.However with that said, having a mix mode design could be useful and much more predicable.1) Design the inner loop(s) using existing Analog domain knowledge.2) Let the CPU perform sub critical functions like real-time frequency monitoring, supply the core oscillator, drive the PWM and offer sub critical PID/PD control functions.Its an interesting subject to experiment with.

author: coppice
author_rank: Super Contributor
timestamp: April 04, 2017, 07:18:31 pm
content: Quote from: diyaudio on April 04, 2017, 07:10:21 pmThere are numerous challenges in creating a digitally controlled SMPS which is rock solid stable under all conditions, but they do exist in large numbers. They are mostly supplies above 1kW, and they are mostly supplies where the customer is prepared to pay extra for the maximum possible efficiency. However, they are gradually creeping down the range. Some PC supplies, and quite a lot of server supplies, are now digitally controlled.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 04, 2017, 07:22:39 pm
content: Quote from: coppice on April 04, 2017, 07:18:31 pmI'm picturing Morpheus asking Neo, from the clip from the Matrix: what is "digitally controlled"?It would be intresting to know what "digitally controlled" means ? are those lines blurred, is it hybrid mix mode like the above mentioned or is it a ti, st, microchip part ect with propriety signal processing code on the flash?

author: coppice
author_rank: Super Contributor
timestamp: April 04, 2017, 07:38:58 pm
content: Quote from: diyaudio on April 04, 2017, 07:22:39 pmPractically everything in a modern digital supply is digital. They may have analogue emergency controls, such as overcurrent protection, although even those features are gradually moving to all digital control. If you want really tight and repeatable control loops for a very high efficiency supply, digital control is the way to go.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 04, 2017, 08:12:31 pm
content: Quote from: diyaudio on April 04, 2017, 07:10:21 pmClearly, it's not suitable for you, but otherwise, my personal opinion about your personal opinion is: bullshit.It's always funny when you are doing something in thereal world, and someone comes and says it's not done in thereal world. Apparently, we live in different worlds.My latest fully-MCU controlled SMPS design has blown power stage FETs once. The previous analog, MCU-controlled iteration blew dozens.It's not that simple to judge. It depends on details, conditions, and the experience of the designer. Most importantly, the field of experience. It's engineering, not politics!In any case, your wording shows you clearly have no idea what you are talking about. It's not a dichotomy ofreal-time softwarevs.analogat all. Modern digital SMPS, completely done inside an MCU, practically always means configuring a bunch of blocks designed to build SMPS controllers, some digital, some analog, to work together. Sometimes there is not a single line of "real time code", whatever it means.For example, peak current mode controller can be implemented so that the most important piece of control is "analog", and it still happens inside said digital SMPS controller MCU. It has the DACs, comparators and PWM generation units capable of triggering from the comparator output. Once configured, no code required to do anything timing-critical. Image on post #8 shows this.Debugging a digital SMPS controller is the best thing ever. You have the visibility! Think about the traditional integrated SMPS controller chip - you have no visibility of the internal signals at all, you only have the huge block diagram from the datasheet, sometimes poorly specified. With the MCU, I can program whatever control structure I want, and I can program any complex scheme of triggering to an interesting event and then storing kilobytes of fast traces which I can print out to UART and plot.Of course, it takes some specific skills to do all this. It's clearly not for everyone; OTOH, switch-mode supplies are not trivial in any case.

author: coppice
author_rank: Super Contributor
timestamp: April 04, 2017, 08:27:12 pm
content: Quote from: blueskull on April 04, 2017, 08:15:23 pmThe other key thing these controller devices have is the ability to get a value from the ADC, perform the loop filtering, and apply updates to the PWM hardware within a cycle of the PWM. This keeps the loop delay really low, maximises the control loop's phase margin, and allows a really crisp impulse response. Devices like the C2000 have many of the qualities of a DSP (e.g. a MAC) but puzzle the average DSP developer, who expects a DSP chip to have extensive DMA functionality. These things are, instead, optimised for tight control loops, typically with all the important work happening in the ADC interrupt routine, or a dedicated hardware path, like the TI CLA module.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 04, 2017, 09:22:03 pm
content: Quote from: blueskull on April 04, 2017, 08:11:00 pmThat sounds TOTALLY insane. A failure at that level is equivalent to a new years eve fireworks show.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 04, 2017, 11:01:01 pm
content: Quote from: blueskull on April 04, 2017, 10:36:20 pmLike I said - INSANE and I will add.....AWESOME.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 05, 2017, 05:29:08 am
content: Quote from: Siwastaja on April 04, 2017, 08:12:31 pmRubbish. Yes you do!. its called an oscilloscope ! the "controller chip blackbox" is not our domain of concern (only the datasheet spec which most people are lazy to read), neither is the MCU register building blocks.You also didn't mention the issues around timing problems created! when you use software break points during debugging such a system.

author: coppice
author_rank: Super Contributor
timestamp: April 05, 2017, 09:24:25 am
content: Quote from: diyaudio on April 05, 2017, 05:29:08 amYou know, its hard to tell when a line like that stems from cluelessness or a troll.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 05, 2017, 11:31:35 am
content: Quote from: coppice on April 05, 2017, 09:24:25 amListen up!if someone doesn't agree with you call them a troll. Please go take a piss!Sent from my GT-I9300 using Tapatalk

author: danmcb
author_rank: Regular Contributor
timestamp: April 05, 2017, 07:12:26 pm
content: where are you getting your 0.4$ prices for C2000 chips from? I have a passing interest in this, mich less demanding application, and I thought I'd take a look at these - but no C2000 chip is less than about 2.50€ here,. and that is in 1000 off. (FEC prices)(edit - sorry - I am mixing stuff. 0.5$ was for STM32F030K6T6 - but that is more like 1.70€ here is 1000 off)

author: coppice
author_rank: Super Contributor
timestamp: April 05, 2017, 07:36:28 pm
content: Quote from: danmcb on April 05, 2017, 07:12:26 pmIf its €1.70 for a thousand, $0.5 should be no problem when buying in quantity.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 05, 2017, 08:24:38 pm
content: Quote from: coppice on April 04, 2017, 08:27:12 pmFor example, using STM32F334, I do the following:Start the cycle at time 0 - set the FETs to current-increasing stateBlank comparator output until COMP_BLANK_LENAnalog comparator triggers the FETs back to current-decreasing stateRinse and repeat.This would work without any code being executed, giving constant current operation with inductor peak current control.At the same time, I do the following in software:Average eight ADC readings taken from the previous cycle. (The current shunt amplifier output pin is connected to an input pin which shares both ADC and comparator functionality, and both can be used at the same time.)Run a control loop on the (small) current error and adjust a current fine-tune parameter.Output the fine-tuned new setpoint to the DAC generating the comparators reference level - the 1 µs DAC has the new setpoint ready for the next cycle.Do the CV control loop (by adjusting current setpoint), if in CV mode.As you can imagine, transient response and stability is brilliant.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 05, 2017, 08:27:10 pm
content: Quote from: diyaudio on April 05, 2017, 05:29:08 amThat's one of the reasons why I have never used a so-called "debugger". I don't need it. I do my own debug structures in code.But I have to add, at least STM32 offers special means so that the PWM generation unit automatically issues safe "off" states to the FETs when the debugger freezes the system. It's just I'm not needing them. I want to keep things as simple as ever possible.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 05, 2017, 08:31:33 pm
content: Quote from: coppice on April 05, 2017, 09:24:25 amMost likely, just a typical case of lack of competence on this particular field, and overestimating one's own skills, leading to this narrative: "I don't understand this so others must be wrong". Something similar to that hilarious Dawn operating system thread, but on a lesser scale. So, an attitude problem. I know very well since I have had (and still sometimes tend to have) similar attitude issues. But attitude issues can be fixed and you can learn new things!

author: danmcb
author_rank: Regular Contributor
timestamp: April 05, 2017, 08:41:00 pm
content: Very interesting thread - disagreements notwithstanding. Thank you, gentlemen.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 05, 2017, 08:47:47 pm
content: Quote from: Siwastaja on April 05, 2017, 08:31:33 pmThat.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 05, 2017, 09:07:14 pm
content: Quote from: Siwastaja on April 05, 2017, 08:31:33 pmlack of competence ? please don't judge me you no where near fit to pass judgment, and rather bombastic about it.Quotethe loop is now running as open loop.

author: coppice
author_rank: Super Contributor
timestamp: April 05, 2017, 09:21:47 pm
content: Quote from: diyaudio on April 05, 2017, 09:07:14 pmHe has completely stopped the loop. As long as there is suitable circuitry in the test setup to catch any in-flight energy at the time the controller is frozen, without damaging voltage peaks occurring, things will settle down. The safe "off" state for the FETs might be driven or undriven, depending on the architecture of the converter. I am not familiar with the ST chips, but I assume they can be configured to deal with that issue.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 05, 2017, 11:55:39 pm
content: Quote from: diyaudio on April 05, 2017, 09:07:14 pmI would not bother getting too upset - there is likely a language/translation challenge that makes it sound harsher than intended. I did agree in general though.Digital controllers are vastly more capable and obviously adaptable at the expense of being a much bigger learning curve up front. They are also very reliable since many critical functions can be offloaded from the CPU to trip various safety ISR's in a reasonably graceful way. If you want to experiment with an all new topology as this thread is discussing - you have little choice but to use digital control. Adding the eGaN FETs add another layer of needed control to optimize the deadtime which is generally much much shorter than you would use on a standard Si FET.The reason I am pursuing digital control in power is because I am always 'between features' on the standard controllers - wishing I could just do a few alterations of the fixed controller here and there. It takes a significant cerebral effort to get any power conversion system to be reliable. I would expect that the OP, who is on the eve of earning a PhD in power electronics, has the brainpower to work out the myriad of details.I for one, am on the edge of my seat waiting to see what the heck comes of this.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 06, 2017, 03:19:56 pm
content: Quote from: diyaudio on April 05, 2017, 09:07:14 pmIt was not meant to be judgemental at all, just made clear that your lack of competence on this particular subject is clearly showing. It's not an issue, not everyone is expert on everything. Hence no judging, just stating the obvious. I like saying it out loud instead of building sophisticated insults between the lines.Your claim that digital, software-defined SMPS controllers are not employed in "real world" but are "marketing" things, is just so plainly wrong it's not even funny. For us who build them, it's a great and everyday way of doing things, with many benefits; and often, it's really the only choice!Digital SMPS design is not trivial and requires certain type of twisted brain, but isn't that true on most complex design things? And who doesn't hate poor documentation of MCU peripherals? But we just need to live with that, and that's part of the competence, not hiding behind the (often factual!) narrative of "this is too difficult". Instead, we need to go forward and be problem solvers.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 06, 2017, 04:54:55 pm
content: Quote from: Siwastaja on April 06, 2017, 03:19:56 pmLast one from me then we will agree to disagree okay? right.okay.The approach that TI and others promote to control SMPS through brute force (high speed ADC, all calculations in digital domain, high speed PWM) results from lack of communication and understanding between analog and digital designers, which in practice turns into unnoticed redundancy.They are trying to generalize control methods and create products for something that cannot be generalized optimally. As a result, after many years of development of products for powerful digital control of analog loops, these still find little or no use for real-world power conversion, people still using old analog control ICs and schemes.Brute force ADC/math/PWM is neither the best method nor the most accurate for controlling the inner current loops of SMPS, it is just the easiest method to describe and sell, it requires huge amounts of digital processing power (and power supply power) because all calculations are moved to the core of the MCU.For example turning a current transformer into a resettable current integrator by loading it with a FET and a capacitor. Then this is wired to a comparator built into the MCU that is configured to act on the PWM module. The other input to the comparator comes from a voltage integrator. Voila! Accurate self-oscillating PFC current loop, without significant use of CPU power. How much MIPS of DSP-ing does this save? In TI chips they just forgot about comparators, there are some disciplines they do not master haha (edit: Looking at F2803x data I notice that there are 3 DACs attached to the 3 comparators, but these DACs do not have a variable Vref, forcing A/D and D/A for any analog gain control. Hilarious. DACs with analog references can be used as real time analog*digital multipliers, saving A/D and D/A.)

author: Siwastaja
author_rank: Super Contributor
timestamp: April 06, 2017, 05:32:35 pm
content: Well, you have a point here.Anyway, a strange thing has happened during the last decade or so: silicon area has become cheap! Like really cheap, and really useful. They can do powerful "brute force" things practically for free, so it doesn't matter.Yes, if you count number of total transistors used for a given solution, it's insane. But it's an irrelevant metric to begin with. Only the cost and capability matters.A digital MCU-based SMPS controller is a straight solution from the first prototype to production for relatively complex, or otherwise special needs where there is no cheap and well known, working control IC available, or the analog control solution would be too large (from BOM viewpoint, cost, etc.).Of course, there is no point in replacing an existing and good analog (most often IC) solution with a digital SMPS MCU when there is zero need to do that. Nobody is claiming that.My latest thing had a kinda niche feature, utterly trivial to implement on paper, but not available in commercial ICs. The first iteration was analog (opamps, comparators, logic gates) with digitally-generated setpoints, the second iteration was digital SMPS MCU. Guess which one hasa lotcheaper BOM, smaller board area, and a lot less issues with corner cases? Guess which one blew fewer fets during development? Guess which one needed only two bodge wires, instead of ten bodge wires, two SOT23 transistors and three 0603 resistors hanging in the air, taking hours to bodge in the 20 prototype units because of one trivial safety feature that was forgotten - don't turn the FETs on until supply voltage has stabilized?Good thing in software is that you can add assertions, safety checks, corner case workarounds very easily and on the fly, and do a software update to all preproduction units. For me, the digital domain has been "safer" and in many senses, easier.In my experience, I feel that I'm totally OK with every issue you have listed; really, the only thing I'm dissatisfied with is dealing with poorly written or broken MCU documentation, poor libraries and/or development software, and MCU errata / silicon bugs.

author: rx8pilot
author_rank: Super Contributor
timestamp: April 06, 2017, 06:00:17 pm
content: The primary reason digital is not yet 'normal' in my opinion is only because it forces a complete understanding of the analog system and how to translate that into code. There are many people that can put a controller on a PCB and get a reasonable result without knowing much at all about how or why it works. Learn the basic rules of SMPS PCB layout, go to TI's webbench and you are converting voltages. When you have a specific need, corner case, step response, power density, etc, etc.....digital offers a clean slate to design for a very specific application with very specific components. There are a great many applications that do just fine with basic controllers off the shelf with next to zero development time. I have some like that. I also have some cases where I need something that does not exist. Having the ability to optimize from very small loads to full loads, transients, efficiency, different active devices, monitoring, safety, reporting and others - is pretty amazing.The unused peripherals and transistors don't matter - they cost nothing and don't take up any space. When you decide to add a feature in the middle of the design or after release - those things are just some code and a couple of extra parts on the PCB. Over time, you may learn more about the circuit or the loads it will encounter and have the ability to make adjustments to compensate. This was very critical for me early on. My power products are connected to a wide variety of loads. Every once in a while, I get the call that something is not working as expected. Usually a false trip of a safety mechanism. I can generally, take a look at the configuration and make some changes to firmware to get past that particular challenge. Nothing else changes except some software thresholds or timings.

author: danmcb
author_rank: Regular Contributor
timestamp: April 06, 2017, 06:23:13 pm
content: If it is like other fields, the benefits of going digital are not just about the technical performance of the thing itself. You already have a uC there, doing other management tasks, if you can put a fancier but still cheap one and lose a bunch of analogue circuitry, that's win/win. And there are things you can do with digital filters that are close to impossible in analogue domain too - i am far from expert on this, but some pretty reliable sources have tried to explain that to me.

author: coppice
author_rank: Super Contributor
timestamp: April 06, 2017, 07:37:31 pm
content: Quote from: diyaudio on April 06, 2017, 04:54:55 pmIn TI's case, the strategy for digital power came from the analogue group (the UCD parts), and customers pushing the C2000 group to add features to the early C2000s, to make a more complete digital power device.Quote from: diyaudio on April 06, 2017, 04:54:55 pmYou would need to explain what you mean a bit more. Digital techniques are much more suitable for the adaptive and non-linear techniques many high efficiency converters use. For converters using simpler linear approaches, they offer a level of long term stability analogue designs demand expensive components to achieve.Quote from: diyaudio on April 06, 2017, 04:54:55 pmYou keep saying that, like its true. Visit any of the big power supply makers, like Delta or Chicony. You'll see that all the high power high efficiency stuff has already gone digital, both for the power converter and the PFC. They expect to bring digital techniques way down into the cheaper supplies, but that requires a reduction in costs. That will come.Quote from: diyaudio on April 06, 2017, 04:54:55 pmDigital control loops are neither easy to describe or sell, compared to analogue. Most power supply customer's are very familiar with traditional analogue techniques, and have taken their time to learn about digital ones. Digital methods are pretty straightforward in the linear regions, but can get rather complex when things saturate. Digital methods do, however, give the most stable and predictable results. I wouldn't call 200-300mW a huge power drain for a device handling the entire control function for a multi-output converter.Quote from: diyaudio on April 06, 2017, 04:54:55 pmThis makes no sense to me. Why would a self-oscillating PFC be a good thing? That's just the way most simplistic analogue solutions have been implemented. Why would saving CPU power be a big deal? Its pretty cheap these days, without incurring high current consumption. Why would anyone worry about saving ADC and DAC channels when they are so cheap? People want to run things from stable references, to ensure stable results across the temperature range, and over time. Nobody forgot about comparators in the F2803x. It was build against the detailed inputs of early adopters of digital power.

author: Siwastaja
author_rank: Super Contributor
timestamp: April 06, 2017, 07:52:57 pm
content: I can see three typical cases that make sense:(1) A super simple analog self-oscillating loop, requiring a few cheap analog components. Think about Joule Thief. Fun to design. Commercially suitable for some specific simple, very low cost applications.(2) A more complex case, but there is a commercial, cheap controller IC available. "Easy" to design using TI WEBENCH... Most power converters today. "Cheap IC" means mass market.(3) Almost anything else: the digital SMPS-oriented MCU is by far the most sane choice in 2017.

author: JPortici
author_rank: Super Contributor
timestamp: April 06, 2017, 09:57:05 pm
content: Let me just say... i'm still a noob at power electronics but i have that same dspic laying around and this topic made me curious. I hate you all

author: Phoenix
author_rank: Frequent Contributor
timestamp: April 07, 2017, 02:50:33 am
content: I'd like to weigh in on this topic - with my experiences.I've been on a team developing a commercial grid tie solar inverter - responsible for the low level loop control and PWM (... yes, I have a PhD in control theory for power electronics). It used two F28035 DSP from TI for the main closed loop controllers. On the AC side the primary current loop is a proportional+resonant - I'd like to see that in an off the shelf chip! The other main AC side PI regulator has significantly non-linear operating modes. There are also other aspects of the converter topology which require other loops to operate in conjunction with the main two loops. Not to mention the PV input controllers (which aren't current regulator based) on the other DSP. Between the two DSPs I think there are about 12 feedback controllers of some form.The company also develops other DC output power supplies using TL431s and control ICs. This is a classic way to do things and is what is well understood in the industry. There is little need for the current power electronics engineers (older generation) to move away from what they know and do.Translation from a control IC to a DSP based approach is also a complete re-think of design and implementation (methodology and skill set). A lot of uC manufacturers try to sell their chips using familiar ideas, but it's never that simple.

author: diyaudio
author_rank: Frequent Contributor
timestamp: April 07, 2017, 08:47:37 am
content: Quote from: Phoenix on April 07, 2017, 02:50:33 amThis!

author: coppice
author_rank: Super Contributor
timestamp: April 07, 2017, 09:24:58 am
content: Quote from: Phoenix on April 07, 2017, 02:50:33 amDid all that complexity pay off in performance? Most people find it does, and by a considerable margin. For something that complex it should also pay off handsomely in reduced cost.Quote from: Phoenix on April 07, 2017, 02:50:33 amThat's the right approach today for supplies which are small, or where people are not demanding top class efficiency. I would guess that in 5 years those guys taking the analogue approach will be limited to supplies below maybe 50W, where nobody is pushing for high efficiency, and where a proper PFC that doesn't mostly exchange a phase shift for a mass of harmonics is needed. In fact, its pretty much the only way right now. There aren't yet enough designers steeped in modern methods. Courses are well attended, though. This will change.Quote from: Phoenix on April 07, 2017, 02:50:33 amI've no argument there.

author: Phoenix
author_rank: Frequent Contributor
timestamp: April 08, 2017, 10:29:48 am
content: Quote from: coppice on April 07, 2017, 09:24:58 amI couldn't do it with discrete parts! The additional complexity is largely to gracefully handle various transient or steady state operating modes that may not be the "nominal " operating state. A good example is having too much PV power available. You need a control method that limits the DC input and achieves exact power balance with the AC output. You can't just set input = output, otherwise you have not accounted for internal losses and measurement/numerical inaccuracy. The flip side is a condition where the inverter is outputting 5kW into the grid (pulling ~5kW in from the PV) and someone turns off one of the PV inputs and you lose 3kW. Suddenly you have a 3kW deficit in input power and the DC bus will rapidly collapse. You don't want to disconnect from the grid under these transients, because it takes at least another 60 seconds (usually longer for other self tests to) to reconnect.

author: Phoenix
author_rank: Frequent Contributor
timestamp: April 08, 2017, 10:35:14 am
content: Quote from: blueskull on April 07, 2017, 03:28:09 amWatch out how you account for delay in the system (PWM moduator delay, sampling delay etc). For every system I've studied it's either been THE limiting factor in bandwidth/margin or a key contributor to pole-zero behaviour.

author: jbb
author_rank: Super Contributor
timestamp: April 08, 2017, 08:42:41 pm
content: Quote from: blueskull on April 04, 2017, 05:39:40 pmThere's nothing like a prototype. When you're getting into special PWM modes etc. it's really important to have a look at the real waveforms. That way you can determine that a chip does what you need.I would then suggest that you do a stage 2 prototype with some enhanced standalone protection: a watchdog timer chip that is reset by main control loop (catches the time you hit pause on the debugger...) and analogue overvoltage / overcurrent trip. I found it well worthwhile when I (re)built the controller for a PV inverter project.Quote from: Phoenix on April 07, 2017, 02:50:33 amYay PR! (This is like a PI with a frequency transformation to place the 'integral' at a particular frequency. They offer some nice advantages over DQ / rotating reference frame designs.) Those things are great. We found that if you have a number of them banked (for harmonic compensation), it seems best to switch them in one at a time rather than all at once.

author: ali_asadzadeh
author_rank: Super Contributor
timestamp: June 06, 2017, 09:29:37 am
content: QuoteI can supply you the part if you need @0.5USD