bmachining

Hi Kell, The supply will be for Hard Anodizing mainly, which takes serious voltage
due to the temperature the baths run at. I will be using a transformer.

Ubergeek, lowest cost isnt necessary. A few $$ on caps certainly isnt going to break the budget.

kell

bgmicro.com has 100uH 13 amp inductors for $1.50, which is way cheap:
http://www.bgmicro.com/index.asp?Pag...OD&ProdID=9584
You could parallel several in a buck circuit of the sort in the datasheet of the chip ubergeek mentioned and get your thirty amps.

Ubergeek63

Nice price...I don't know how long they stay there as BG does not look like the sort of place that has anything regular-all special purchases.

Ubergeek63

Well that certainly makes it easier to find parts... you are looking at losing 60W in a 50A bridge, 50W in the freewheeling diode, and 50W in the FET.

The losses are one reason there are a lot of off-line switchers. Some of the parts cost more but the losses go down, at least in the bridge. The losses in the FET are harder to guess at, but the losses in the bridge go down to 10W in a 10A bridge at 240VAC input.

It is hard to say what a hand modded switching transformer would act like. There are batch variations even in machine wound ones!

bmachining

Nice link, thankyou!
Help me understand this a little better....
Is the Fet being supplied AC or DC? If AC then do we need a Bridge rectifier after it to get the DC?
If its DC then obviously the bridge is before the Fet.

Loosing some efficiency isnt a big issue, it usually goes in heat i imagine, can always compromise!

Ubergeek63

Transformer-bridge-BIG cap-cap-inductor-FET-diode-cap

The two little caps are for the high frequencies,although little is a relative term.

If you are actually putting out 1200W DC, the transformer and the line will see around 2KVA. That is why there are so many governments bowing to the utility companies demand for PFC. It is much easier to supply power more efficiently than it is to replace all the lines and transformers when they blow.

Ubergeek63

on the output side you probably want 100uF minimum at 50VDC and 30A RMS if you want real reliability, though 10A RMS is probably plenty. A similar value on the input, though the RMS is not as critical.

The higher the cap and inductor values the lower the ripple. If you are actually running CCM the cap RMS requirements are much lower. It would be more normal for that chip to be running CCM.

bmachining

Do i need a special type of diode? i did a search for 50A ones, but theres moe types than i realise.

Parts list so far,
HV9910BLG-G driver
STW120NF10 Mosfet
ECE-T1KP153FA Cap
100uH 13.2A Choke 3 of


a few smaller caps, resistors, diodes, pot, .......

Anything obvious missing?

Ubergeek63

the 9910 is a regulator...you need a mosfet driver as well

bmachining

High side or low side?

bmachining

Would this diode be suitable?
http://search.digikey.com/scripts/Dk...me=RURG5060-ND

Ubergeek63

That diode will do quite nicely. The data sheet says to use a FET with less than 15nC gate charge...that is why you need a gate driver, noninverting low side.

http://search.digikey.com/scripts/Dk...AN3100CSXCT-ND looks like a nice one. It is SMT but at least it is only a SOT23-5 so it is still reasonable to solder to.

bmachining

Thankyou again!

I assume the input voltage wont be a prob, as it wont be directly connected to the 40v side.

Now come the fun bit!!! See if i can source these easily in Australia, and attempting to draw up a circuit.

Ubergeek63

Well I was assuming you would be able to order through digikey...

bmachining

Yeah that would be the easiest! The regulator i cant find in digikey, i would prefer to get all from one place, to save on the sometimes exorborant international shipping prices.

Any suggestions for an online downloadable program so i can attempt to draw this up?