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Converter topology selection

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Rookie_poweran

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Hello, I want to design 150v-420v dc input and 48v output converter about 550w output power. Unit cost of converter is important. Which converter topology best fits with this kind of application?

Thanks
 
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an half bridge or full H bridge with transformer will give you full control - and protect your load from a shorted device

A simple buck can work - but if the mosfet goes short the load sees the full Vin
 
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Easy peasy said:
an half bridge or full H bridge with transformer will give you full control - and protect your load from a shorted device

A simple buck can work - but if the mosfet goes short the load sees the full Vin
Click to expand...
Thank you. Is there any controller that you know for hb or fb? It can be done with hard switching with Sic s right?
 
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UC3856, any mosfet with the requisite voltage and current rating and sufficient heatsinking - if hard switching remember to start with Ron = 33ohm, and a back diode for fast turn off.
 
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Also, , is you power source the mains...if so...then why not do Boost PFC stage up front?...then you only have vin=400vdc.
Also, you get lower current in the wires to it.
Then you may do 2 tran forward.
But it depends to some extent on your enclosure details, space constraints, and ambeint temperature where it will be run, and whether you are allowed to use fans to cool.
The UC3856 is very good but no overload shutdown with hiccuping. A simple current mode controller eg NCP1239 can give you this.....it only has one output for fet drive, but you can use a d type cct to give you the two outputs. Please ask if you want me to send sim of this in free LTspice.

You can do your own hiccup cct, and use it with uc3856, but its more components than the d type thingy.
Also, NCP1239 has UVLO.
 
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Easy peasy said:
At 550 watts and running off 420V DC input - the push pull sees 840V on the drains + spikes - so not the best choice here.
Click to expand...
Snubber and IGBT can handle that voltage. Only full bridge can manage that voltage easily, but will be too expensive for that power. 2-Switch Forward will be limited by duty cycle due to the 150V input minimum, Interleaved Forward can, but will be too expensive too.

Please suggest the right topology.
 
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Easy peasy said:
At 550 watts and running off 420V DC input - the push pull sees 840V on the drains + spikes - so not the best choice here.
Click to expand...
Resonant converters are difficult to design in combination with wide input voltage range. So, they are typically designed with a PFC pre-stage. The input voltage is DC , adding pre-boost DC-DC will also be expensive.
 
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The pushpull appears to offer the golden chalice
of D>0.5 but with no high side drive, and only two fets.
A river of SMPS gold...
But as we've found, its a badboy in disguise. The leakage inductance loss will be great
, and due to the high off state fet voltage, its awkward to snub it, without getting
big losses in that snubber. Then we say, ok, we can just interleave wind it....right?.....
no...An interleave wound push pull needs six coils, as both secondaries need interleaving with
their respective primary. Makes the transformer too expensive.
Unfortunately The pushpull is a badboy converter.
Try winding the push pull such that each primary is well coupled to its secondary and the other primary.
Yes it can be done, but ....rather do a full bidge instead...or a two transistor forward with a special
, cheap, low power, regulated bias supply which permits duty cycles >0.5.
 
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Easy peasy said:
We design resonant converters with wide range inputs - however the half bridge hard switched will also work here and is a lot less effort in understanding for the OP.
Click to expand...
Resonant will need pre-regulator to meet that input voltage range. With that power, output voltage regulation will be a challenge , will require complex tuning. Additional high side Gate driver cost and Half bridge will require bigger output inductor.

Half bridge can be a good topology option, but due to the main design consideration of cost and simplicity, I still prefer Push-pull with IGBT
 
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Yes Half Bridge Hard switched........and we all know it can be done with current mode and sufficient slope compensation...just be sure to use caps rated for the full rail voltage "just in case"...(eg overload etc).
But there will always be that niggle that behind it all...there is no real hard and fast proof that Current mode with "enough" slope comp works for half bridge.
(there are "proofs" available on the web, but whether to believe or not..)
And voltage mode comes with the issues of voltage mode.
 
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At 550 watts the dual resonant forward is a contender also - as it reduces input ripple and has easy control - the EMI signature is much lower than a hard switched push pull with > 900V on the fet or igbt drains ! ! !
So . . .
 
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Adding Vin feed forward to the half bridge ramp - is very much like adding a current ramp ( mathematically identical ) and gives instant correction for Vin ripple

It allows volt loop correction to be very good indeed - and you can add a conventional current limit circuit to the output . . .
--- Updated ---

The OP does not state where the DC is coming from - although it's a fair guess it's from 90 - 275Vac mains ....

The PF can be cleaned up with a choke in the AC line - or just ignored - just like millions of other 500W converters out there.
 
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Also, an easy option is the fixed step down LLC, with follow on Buck converter to give the final reg to 48V.
So the LLC steps down 2:1....then the simple, synchronous buck does the rest.
So the buck will deal with vin = 210-75V.
Make it a sync buck when in higher load region.
Synchronous operation is easy with a buck...compared to isolated converters.
The LLC gives you isolation efficiently.
The sync buck is pretty good with efficiency too.
 
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Easy peasy said:
At 550 watts the dual resonant forward is a contender also - as it reduces input ripple and has easy control - the EMI signature is much lower than a hard switched push pull with > 900V on the fet or igbt drains ! ! !
So . . .
Click to expand...
IGBT are typically rated at 1200V as Mosfet replacement for high voltage application.

150v-420v dc input and 48v, that is the requirement for input voltage range. so PFC pre-regulator is out of scope.. 150Vdc - 420VDC input voltage range, and 48V Output. LLC will be unstable for any decent output voltage regulation.
 
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