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5th September 2019, 09:23 #1
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Looking for a suitable DC DC buck conveter topology
Hello there,
Anser this post who knows Power Electronics well.
Take a look my buck conveter in attachment.
People may called it "Dropper'
It has following properties,
1. Input is 120 to 160 volt DC/ 30 Amp.
2. Output must be 110volt/30 amp(maximum). + 5% regulation( contineous output should be 20 amps)
3. Isolated in both input and output circuit.
4. Shunt sensing.
5. proper feedback.
6. 2 switches gets OFF/ON alternately.
7. May be soft switching.
8. May be 90% efficient.
I am thinking to modify it because bulky reactor/coupled inductor.
It has high current application.
kindly suggest a design that has
1. Less switching losss.
2. Less stress on switch.
3. Less number of component.
4. ZVS or ZCS idea.
5. Suitable ripple minimization.
6. Suitable couple inductor design.Hasan

5th September 2019, 10:32 #2
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Re: Looking for a suitable DC DC buck conveter topology
you are missing the diodes on the LH side for a buck converter ( interleaved )
with the diodes added the ckt will work OK and meet your specs  will need caps on the i/p too
you cannot couple the L's in this ckt

5th September 2019, 11:22 #3
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Re: Looking for a suitable DC DC buck conveter topology
Coupled inductors have repeatedly suggested in literature for interleaved buck converters, see e.g. https://www.researchgate.net/publica...rter_POSTPRINT
In the general case, coupling factors of 0.6 to 0.7 are implemented.
As for the other points, there's no simple way to implement soft switching in this topology.

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5th September 2019, 11:50 #4
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Re: Looking for a suitable DC DC buck conveter topology
I have yet to see one that works very well, or has the same self shielding as, say, 2 x RM14 cores ... a lot of these papers never consider EMC aspects ...

5th September 2019, 15:17 #5
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Re: Looking for a suitable DC DC buck conveter topology
Nice to get your feedback.
Can not we raise " Phase" in DCDC buck action.
Because of 2 switch? Multiphase but not interleaing?
Looking at this circuit it seems like a 2 conventional buck converter working at a time or alternately ! Need to analyze both DCM and CCM mode for the inductor. If its not coupled inductor that means 2 inductors are not magnitically coupled!
Can you see any " transformer" action on it?
As its output and input currents are same, then yes ! Voltage should be control.
Interesting to see its ON and OFF circuit. What would be the charging and discharging path in this circuit?No freewhiling action? 2 capacitors are helping charging or discharging through to load?
Input power isolation has done with some transformer and optocoupler.
Output can monitor by shunt sensing.
Couple inductor is more cost effective but high current and voltage need to be carefully solve. High current IGBT is only solution?
For HVDC application people use many IGBT in sequence !Hasan

5th September 2019, 17:28 #6
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Re: Looking for a suitable DC DC buck conveter topology
I suggest putting the voltage detect on the output side of the shunt (right side in your picture) instead of the
regulator side (left) as you want the output voltage, to be correct, not a little low
I suggest the current shunt resistor be in the low side (), instead of the high side (+)

5th September 2019, 18:52 #7
Re: Looking for a suitable DC DC buck conveter topology
In your properties list, you include the following:
3. Isolated in both input and output circuit.
This means a transformer requires to be used.
Transformer switchmode topologies include pushpull, half bridge, and full bridge.
Either ZVS or a ZCS are suggested for the higher power bridge topologies, but they are technically challenging.
I will give you the best advice: Search the TI website for full bridge controllers. Study some of the datasheets and app notes. Using paper and pencil, or an Excell spreadsheet, go thru all the design equations and solve all the variables and select appropriate components. Simulate a circuit or two.
And you have not even touched thermal management, EMI concerns, board layout with safety issues in mind, protections and monitoring.
I am not attempting to scare or dissuade you. But you must be aware of the significant technical challenges, and determine whether this is a project you can actually complete succesfully.My batteries are recharged by "Helpful Post" ratings.
If you feel that I've helped you, please indicate it as a Helpful Post
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6th September 2019, 01:42 #8
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Re: Looking for a suitable DC DC buck conveter topology
1 members found this post helpful.

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6th September 2019, 09:50 #9
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6th September 2019, 11:47 #10
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Re: Looking for a suitable DC DC buck conveter topology
I ignored the "isolation" point in post #1, because it makes no sense related to the diagram. If isolation is required, "Isolated in both input and output circuit" makes still no sense. There can be isolation between input and output, but what does "both" mean. Possible isolation of control circuit and e.g. gate driver is a different topic and not directly related to power circuit isolation.
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6th September 2019, 12:45 #11
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Re: Looking for a suitable DC DC buck conveter topology
Mr. FvM,
Take a look on this transformer ,
Could you guess something ?
For your full understanding, isolation means output and input can work without effecting each other.
The people who read "Power Converter" can easily recognize what I am saying, even I did wrong in post.
   Updated   
Depending on power density and application, I want to change this converter.
Looking for a solid usable topology.
I think this basic diagram is confusing!
Its an old design.
Hall effect IGBT sensor might cause some problem in sensing. OP AMPs are back dated, so may be malfunction occurs.
I will let you know what actual problem exists in this design.
IHasan

7th September 2019, 03:43 #12
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Re: Looking for a suitable DC DC buck conveter topology
From your transformer diagram  you have a pri wdg and a sec wdg ( centre tap ) for the power transfer and then an auxilliary wdg on each side too  for local control power ...
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7th September 2019, 06:44 #13
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Re: Looking for a suitable DC DC buck conveter topology
Yeap!
Well said.
Now depending on the winding/ turns cant you tell what what would be the converter type?Hasan

7th September 2019, 11:51 #14
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Re: Looking for a suitable DC DC buck conveter topology
that transformer is not good for much ...
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8th September 2019, 13:04 #15
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Re: Looking for a suitable DC DC buck conveter topology
I do appreciate your analysis and effort you did here!
Yeap! This circuit is nonsense indeed.
Because of ...
1. No freewhiling path/ diodes.
2. Energy storing device alignment is wrong for sure.
3. Inductors are parallel, means it fails to describe wheather its bridge type or flyback type.
4. In this application, user must think a power transformer with center tap winding in sencondary!
5. CCM or DCM mode circuits cant be explain, because stupid circuit path.
Lets move our mind from this design to this follwing one ( its from a knowledgeable researcher)
Can you feel anything clear from it?
1. Input coupled inductor maintains isolation?
2. For the ON/ OFF of switch( Mosfet/ igbt/)
, free whiling paths is notiable.
3 . More simple that might not require ZVS, ZCS.
4. Gain equitation can be possible to find.
5. Interesting to see how the parallel capacitor shows the advantage.
6. For this kind of high current application, not sure the switch would be long lasting or the inductor size!
What do you think sir?Hasan

9th September 2019, 00:35 #16
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Re: Looking for a suitable DC DC buck conveter topology
it is not isolated ....

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9th September 2019, 09:26 #17
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Re: Looking for a suitable DC DC buck conveter topology
it is not isolated ...Hasan
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