12VDC-48VDC Boost Converter Design/Controller Suggestions - Page 1
Forum section: electronics / projects

author: kjn
author_rank: Newbie
timestamp: May 24, 2020, 05:00:29 am
content: Disclaimer:So I am a mechanical engineer by trade, so analog electronics is most definitely not my thing.I have some experience with microprocessors (mostly arduino-esque), but not much.I am using my current covid induced downtime to learn some new skills and work on some projects.I've run into a bit of a wall with a design I am trying to solve with respect to a battery charger.I have been testing using one ofthese. But I now have to work on making something more suitable to my application.I am wanting to design a boost topology DCDC, my rough functional requirements are:*11-16VDC Input*48V nominal Output*4A Nominal, 7.5A Peak Output (lets say 300W nominal)*Very high efficiency (>%95)Design Requirements are:*Compact/Minimal Board Area*Minimal BoM*Monitor output voltage*Monitor output current*Monitor Fault/OK conditions*Adjust output via CV or CC - or set limits?*Ideally via i2c/SPI or similarMost of this is pretty easy to achieve,TI's power designertakes alot of the hard work out of this for me.So it would appear that I could almost turnkey a design that meets most of my design spec from this workbench (ala LM5122), apart from digital control aspect - this I am struggling with.I considered adding an additional monitoring circuit (via INA219) however, now you run into issues due to the relatively high DC voltage, and it seems redundant as most of these controllers are already using a shunt and voltage monitoring for feedback. I'd rather not add any more parts than I need too. Surely there is an integrated DCDC boost controller that would include such functionality? My google-fu has let me down, no doubt to my inexperience in the area.Any part suggestions, design resources?Thanks

author: Mazo
author_rank: Regular Contributor
timestamp: May 24, 2020, 08:58:38 am
content: While I can't suggest a immediate solution,I think there are a few points you should specify more in detail:Quote from: kjn on May 24, 2020, 05:00:29 amHow long should be the peak output?There are 3 cases:1-Pretty short-the increase in output current is supported by the energy in the output capacitors(slight drop in voltage ofc,how much of that is acceptable is your decision)-the converter can't support both electrically and thermally the peak output but can the nominal+a few hundred mA say.2-Medium in length-The converter can support the peak electrically but not thermally-the peak output should stop before overheating occurs.(Somewhat harder here to say how long is that)3-Long to infinite-The converter supports the peak output current both electrically and thermally-the best case but means designing a 7.5A converter not a 4A one.You can still optimise for efficiency at the 4A mark as your efficiency requirements are highish.Quote from: kjn on May 24, 2020, 05:00:29 amYou should definitely set some bounds on that as in general variable output converters are either limited in tuning range or you are soon forced to compromise on some other aspect of the design.About the chip selection-if you run into a chip that can support 24V output but not 48V you can use tapped boost topology(1:1 inductors are easy to find off the shelf).The digital control can be realised with 2 external DAC's as I would say there are way more chips that provide for some kind of analog current limit/output voltage control.Also as the power output you are requiring is in the few hundred watts,search for controller not converter chips.Good luck

author: kjn
author_rank: Newbie
timestamp: May 24, 2020, 10:49:38 pm
content: Hi Mazo,Thanks for the input - to clarify:QuoteMy use case would only really ever be 1 - 4A is really my absolute maximum target. 7.5A is a calculated rush on load connection. I expect a moderate bank of capacitors will manage this, certainly in the Ti reference design it was achieved this way.QuoteRealistically +/-2 V on the output, CC control is not a necessity but nice to have.Certainly there are alot of frequency switching SMPS Boost controllers around - I am confident I can learn and build the supporting circuitry.All the controllers I can find are quite "old" and are dumb controllers (e.g. set by feedback voltage) - I really would have expected to find a controller that intergrates some of these features.I have changed the post topic to be clearer as I dont think I did a very good job.

author: Mazo
author_rank: Regular Contributor
timestamp: May 24, 2020, 11:31:25 pm
content: OK,so +-2V is a little change considering the nominal of 48V,you can just design for 50V output voltage and max current and just later slap on the variable part of the output voltage control.(If you make a reasonable design for 50V out,it will be reasonable for 46V also).The CC part,think twice if you needcurrent limitedorconstant currentoutput.Also what should be the behaviour of the device when it hits the current limit/constant current threshold.Should it latch off,hiccup,foldback or lower the voltage to maintain the output current(constant current)Another point to consider-Whatever your current sensing method it is it should obviously support currents in the ampere range,which means it will not measure at all or measure with highly degraded accuracy currents in the mA and below range.Roughly the way I would go if I am given these specs is:1)Design a normal boost that supports 50V @max long-term current output and minimum input voltage.2)Add a DAC and whatever circuitry around it is required at the feedback point to change the output voltage.3)Decide on the behaviour of the converter when subjected to overcurrent at the output.4)Modify the circuit to get the desired behaviour when subjected to overcurrent when being careful to not push the converter outside it's comfort zone(too low/high duty cycle for example is a problem).This approach will give you alot of knowledge and experience,but might be too much for someone who doesn't have much experience and will consume alot of development time.The other option I see as viable is too find all converters that are I2C/SPI controlled(that would filter a significant part of them) then filter them by supported input/output voltages(in the voltage ranges you are looking for there are alot of LED backlight driver chips,but they aren't generally suitable for something other than....led driving)If you find something that fits you perfectly great-(I don't think there is a perfect fit for that kind of requirements as in a single chip solution)Otherwise you would either have to compromise on some aspects of your requirements or take the first approach.As for the LM5122-as many other converter chips it seems controlled by analogue means,so you will have to use DACs and Digipots.Got a little carried away

author: NiHaoMike
author_rank: Super Contributor
timestamp: May 25, 2020, 01:58:44 am
content: Good starting point:https://sound-au.com/project89.htmHow I would adapt it to your requirements:* It has bipolar output while you only need unipolar output. Remove the bottom two diodes and associated capacitors.* It uses a transformer, but an autotransformer is much smaller for the same power output. First step: imagine that the secondary is removed and the diodes connect across the primary. That will yield about 24V, about half of your requirement. Fix that by adding windings between the ends of the primary and the diodes.* The output relying on leakage inductance to limit peak current can work and is often done in power inverter designs, but you might want to add an inductor between the output diodes and capacitor, especially if you're new to magnetics design.