Common Power Supply (DC/DC) Topologies - Page 1
Forum section: electronics / general

author: butech
author_rank: Contributor
timestamp: April 12, 2021, 02:23:39 pm
content: Hi,I am interested in your opinion and/or experience regarding the "state-of-the-art" power supply topologies used these days in the power range of about 1W to 20 kW. Although I work now for >10 years on power supplies, there are some topologies, which I think, nowadays are just found in textbooks and not in the industry. E.g., I have never seen a hard-switching half-bridge dc/dc converter (just ZVS LLC) in a project, a hard switching full-bridge (just as ZVS phase-shift or as H-Bridge for DC motor drivers but not in an actual SMPS), and also the single-ended forward converter seems to vanish (although I have seen them in older days 10 - 15 years ago in some designs).Therefore I am curious about what you think, which topologies are up-to-date. My perception is that the following topologies are most frequently used:- buck and synchronous buck- flyback (mostly DCM, quasi-resonant, and active clamp)- boost converter (mostly for PFC and sometimes in low voltage applications)- LLC resonant converter (half-bridge and full-bridge)- ZVS phase-shift full-bridge- two-transistor flyback and two-transistor forward- active clamp forward- SEPIC (low power only <50W mostly battery-operated equipment)What is your opinion is my perception wrong or am I biased? Which topologies do you think a designer should know these days?

author: aksg81
author_rank: Newbie
timestamp: April 13, 2021, 10:18:14 am
content: You missed dual active bridges for Isolated bidirectional applications but other than that I agree. I have also heard from more senior folks that for a given "type" of application and power level there's not much choice of topology.

author: megajocke
author_rank: Regular Contributor
timestamp: April 13, 2021, 11:21:05 pm
content: I was surprised to find a single-ended forward converter in a Mean Well SP-500-24, a 500W 24V power supply.Switching transistors are two 2SK3878 in parallel. If I remember correctly it connects the clamp winding and diode through a capacitor to the power winding/mosfet drain to effectively clamp turn-off voltage spikes.I measured switching frequency and it was 62 kHz.PWM controller TL3845P.PFC controller LT1249.SP-500-24 is out of production since a few years back, but I wonder if the PSP-600-24 in current production with the same form factor is similar (or if they went to a two-transistor forward maybe?).Hard-switched half bridges are definitely not as popular as they used to be with that self-starting BJT circuit found in almost all AT and old ATX power supplies. The topology doesn't lend itself easily to current mode control without special arrangements and more or less requires a current transformer to monitor switch currents and not blow up during overload.And as switching frequencies rise and transformer flux-swing becomes limited by core losses rather than saturation, the bipolar excitation isn't much of an advantage any more either.While the winding utilization is less in a forward converter because of the non-power-transferring DC current component in the windings, at the same time the DC current isn't subject to skin/proximity effect losses. As DC resistance can be quite a bit lower than AC resistance, the DC current in the winding doesn't cost that much either.I think these reasons - easier current mode control and current sensing in addition to that unipolar excitation and DC current in the windings don't give much disadvantages at higher switching frequency - are what has led to the widespread adoption of different types of unipolar-drive forward converters (dual switch, active clamp, single switch) and the decline in use of hard-switched bridge converters.

author: jonpaul
author_rank: Super Contributor
timestamp: April 17, 2021, 12:45:53 pm
content: The choice of PSU topology depends on many factors, efficiency, cost, EMI, required input and output voltages, etc.The trend in recent years is towards higher F and soft switching, resonant and Class E.The micgation of frequencis seems to be ~ 10X per 1 - 2 decade, eg 1960s 20 kHz, 1970s 100K 1990s 500K 2020 1 M-50MThe recent GaN and SiC devices have also made the higher frequencies proactical.We have used foward and double foward at ~ 500W..3 kW in 1990s.Of course the EMI treatment, component choice and ease of semiconductors also affect the design.Bon JourneeJon

author: ocset
author_rank: Super Contributor
timestamp: May 02, 2021, 05:04:52 pm
content: Hi,I actually sent a big reply to this post but its disappeared.Anyway...please find my SMPS course, wherein there is a folder on half bridge.Half bridge in current mode actually works ok as long as theres enough slope compensation.https://drive.google.com/file/d/0B7aRNbu3Fes4TU92Mkw3YlA3ams/view?usp=sharing...there are controllers like LM5039 which has average current mode in overload, (for half bridge) but it never really caught on, as standard current mode with overload protection and slope comp can get through overload.(BTW i am wondering how my approx 30 line reply went missing from this thread...is there any way you can tell when you logged in to this site in the past?...as someone may have hacked my password and deleted my post)

author: ebastler
author_rank: Super Contributor
timestamp: May 02, 2021, 05:32:13 pm
content: Quote from: treez on May 02, 2021, 05:04:52 pmNothing to do with your account; it was a general mishap. Many people noticed this morning that their post count had suddenly dropped. Dave chimed in and explained that he had tried to change something in the backend and accdentally deleted quite a few threads. He now seems to have used a not-quite-current backup -- trying to restore the lost threads, but on the other hand losing some recent posts to threads which had previously gone unharmed.There was a thread earlier today where this was discussed, but I cannot find it now. Maybe it also fell vicitm to the restore operation?

author: PKTKS
author_rank: Super Contributor
timestamp: May 09, 2021, 11:33:33 am
content: In older times... before the highly integrated anddedicated "supervisor" ... folks just collectedreferences for ISOLATED DC/DC convertersinto a FLYBACK class..letting Buck/Boosters to the facto NON ISOLATED ones.Today it seems some purists freak out when youcall an ISOLATED DC/DC a FLYBACK...nevertheless it seems to me very commontoday that the RCC flybacks (ringing choke converters)as one the cheapest and more common alternativesfor converters...cheap it is .. but also a crappy regulator..RCCs are very common these days evenhaving dedicated ICsPaul

author: f4eru
author_rank: Super Contributor
timestamp: May 09, 2021, 08:57:10 pm
content: 'never seen an LLC converter being called "flyback"

author: PKTKS
author_rank: Super Contributor
timestamp: May 09, 2021, 09:04:03 pm
content: And should not...As they are pretty recent in audience..This nomenclature dates back to TV sets70s 80s all discrete...Different viewsPaul

author: ocset
author_rank: Super Contributor
timestamp: May 15, 2021, 09:23:07 pm
content: QuoteI think you are right....your list can do most jobs....but there is one that its a mystery that its not used much, and that is the asymetric half bridge.Also, i reckon the plain half bridge is good as with a bit of slope compensation in current mode you dont get split cap unbalance....and the standard half bridge lends itself well to bootstrap high side drivers....so for say that "grey area" of 100-200w i recon the half bridge is a good one....you can sometimes get away with doing it without fet/diode heatsinks....whereas you might need them with a flyback

author: xavier60
author_rank: Super Contributor
timestamp: May 16, 2021, 02:02:48 am
content: Something I saw in a laptop AC adapter. It was constructed as half bridge converter with output choke.Instead of varying the duty cycle in the conventional quasi-square-wave way, the controller varied the duty cycle of the whole waveform.The dead time always stayed at minimum.

author: Hrod_Wolf
author_rank: Newbie
timestamp: May 21, 2021, 12:26:28 pm
content: Hi,Have you ever heard of the FLYWARD topology which is a combination of a FLYback and a forWARD for bidirectional DCDC converters ?We have in this a buck mode conversion one way and a boost mode conversion the other way.This may be a french patent but I don't know if it has been implemented on a vehicle yet.

author: ocset
author_rank: Super Contributor
timestamp: June 06, 2021, 10:59:41 am
content: seen plenty of literal buck one way boost the other way's......its basically a 4 switch converter and depending on which ones you activate you get the buck or boost the other way.For EV charging both ways....the one ive seen is the Dual active bridge....its kind of like a full bridge but with significant leakage inductance........you can go either way with it.I think the full bridge is phase shift controlled.

author: chris_leyson
author_rank: Super Contributor
timestamp: June 06, 2021, 12:56:02 pm
content: Flyward topology isn't one I'm familiar with, designed a fly-buck a few years ago to replace two cascade buck converters that overheated and died at high ambient 85C due to poor overall efficiency. The buck inductor was three We-flex windings in parallel for 5V and the other three windings in series for the higher voltage 14V output. Overall efficiency was 80% which was a big improvement over original 65%.Cuk is a nice coupled inductor topology as input and output currents are non pulsating.