30V/5A SMPS IC tips/ideas?

[justanothercanuck]

So a while back, I was debating on whether I wanted to buy a bench supply or build one myself.  I didn't like the prices for my local offerings, so I was considering making a supply myself using something like the LT3080/3083, that was until the whole thing about the regulator being a bad design or something.  At any rate, I got busy, had to move, and it got put on the backburner with all my other projects.

Anyways, I wanted to dig up the bench supply idea again, and thought about going the SMPS route.  I'm still looking to have the supply operate at 0-30V/0-5A, so I'll need something I can parallel up in buck or buck-boost mode.  I had a look at Maxim, TI and OnSemi, but sadly I'm still lost.  Some of these IC's have all sorts of features that I probably don't need (ULVO, soft start, on/off control, auto restart), or their voltage or current output are too low for my design intentions.

Anyone got tips for choosing a SMPS IC?  Thanks 

(Yes I know I should probably just buy a bench supply at this point, but I don't have any decent local stores, and shipping can be expensive, even in Canada, especially if it's imported from the US and I have to pay duty...  ugh I hate shipping.) 

edit: doesn't help when sites like Mouser list an IC as having 3A output, to read the data sheet and find out it's only good for 100mA.  TL5001, I'm looking at you... 

edit: actually, I think I may have figured it out...  I can use the LM2678 to get to 30V if I use a voltage divider on the feedback pin and group the outputs together between the LC circuit and the feedback resistors. 

[justanothercanuck]

I was going to buy a 120V to 48V/250W transformer, and do full wave rectification.  Should be enough headroom to run the IC's at the full 30V output, and even if it's not, I probably won't need the full 30V enough for it to matter.

On the other hand, I'm looking at part prices...  the IC's are $7 a piece (x2 if I want 5A without running them at full blast), a transformer is like $115 (let alone the shipping for something that almost weighs 10lbs - edit: $46 shipping??  Get out of here...)  Starts getting into the pricey territory, but I would have had to buy the transformer either way I suppose. 

[void_error]

I was going to buy a 120V to 48V/250W transformer, and do full wave rectification.  Should be enough headroom to run the IC's at the full 30V output, and even if it's not, I probably won't need the full 30V enough for it to matter.

On the other hand, I'm looking at part prices...  the IC's are $7 a piece (x2 if I want 5A without running them at full blast), a transformer is like $115 (let alone the shipping for something that almost weighs 10lbs - edit: $46 shipping??  Get out of here...)  Starts getting into the pricey territory, but I would have had to buy the transformer either way I suppose. 

36V/250VA is probably enough, you'll get about 50V after rectification/filtering at no load assuming a 120V input. If you're running the whole thing without a switchmode pre-regulator expect to spend some $$$ on a beefy heatsink and a truckload of output transistors...

[peter.mitchell]

I know building one seems like a lot of fun and all and you *could* save some money, but really i'd just get one of these and be done with it.

[justanothercanuck]

I know building one seems like a lot of fun and all and you *could* save some money, but really i'd just get one of these and be done with it.

Yeah, I know.

Why are the output posts on the back? 

[void_error]

Why are the output posts on the back? 

So they could fit their big fat logo

[justanothercanuck]

This might fit the bill for me...

http://www.ebay.ca/itm/ZXY6010S-DC-Constant-Voltage-Current-Power-Supply-Module-60V-10A-600W-w-TTL-/111020252080
http://www.mhinstek.com/product/html/?98.html

For all I know, it's a piece of crap, but it's only ~$100 and all I would need is a reasonably-sized wall-wart to power it.

I was looking at their B3008, but apparently . 

[Christopher]

Instead of an iron core transformer, how about a high quality laptop charger? Most of these are 19 at various output powers.

A buck boost with digital pot feedback would be a great addition

[void_error]

Instead of an iron core transformer, how about a high quality laptop charger? Most of these are 19 at various output powers.

A buck boost with digital pot feedback would be a great addition

Laptop chargers usually output less than 100W, unless it's a gaming laptop, but those don't really go above 150W.