Electronics > Beginners
Transformer specs. (Answered)
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spec:
Thanks for the info- very useful :)
not1xor1:

--- Quote from: xavier60 on November 17, 2018, 11:07:28 pm ---The elimination of diode voltage drop with the use of the LT4320 and four mosfets will make the 2 x 15V transformer more likely to maintain regulation at full output voltage and current.

--- End quote ---

another member of this forum, Liv, designed some very good PSUs using just a couple of LM393 as driver for the mosfet rectifier bridge.
https://www.eevblog.com/forum/projects/diy-bench-power-supply-psl-3604/msg623000/#msg623000
LT4320s are relatively expensive.
mariush:
They're not THAT expensive.

LT4320 is around 6$ if you buy 1, 4$ if you buy 25
A good bridge rectifier (rated for 10-20A) is around 1$ if you buy 1, a heatsink for it would be another 0.5$ ... so you're looking at 1.5$ vs 6$

Those 20-30 components he uses to build the equivalent of the LT4320 would probably cost 2.5-3$ if bought from a distributor, simply because you're ordering small quantities of a lot of different parts. He already had some of the parts before, maybe he ordered some components locally... whatever.
Then there's also the amount of space used on the circuit board... but circuit boards are cheaper these days.. the extra circuit board space is probably less than 1$, depending on where you order the board from.   

That guy's problem was that he's living in Belarus, and therefore ordering online is difficult and shipping to him is costly. For these reasons, he had to work with parts he can easily purchase locally or pull from other hardware.

For others, shipping is free  or cheap... for example farnell and rs-components and tme.eu have very reasonable shipping costs to MY country (Romania), something like 4-5$ per order, regardless of how big the package is. So, if someone orders all the parts for that power supply, or orders 100-200$ worth of electronic components, paying less than 5$ on shipping is not a big deal. 

Even Digikey has free shipping from US if you order 60$ or more (well, it was like this around 1 year ago when I last ordered) but I admit it was an annoyance having to go to the local DHL office (at the airport, at the outskirts of my town, around 5 miles/ 8 km) to pay around 2-3% of package value in customs fees and 20% in VAT.  Maybe things have changed since then but these days I mostly order from farnell and tme.eu
 


not1xor1:

--- Quote from: mariush on November 19, 2018, 08:33:39 pm ---They're not THAT expensive.

LT4320 is around 6$ if you buy 1, 4$ if you buy 25
A good bridge rectifier (rated for 10-20A) is around 1$ if you buy 1, a heatsink for it would be another 0.5$ ... so you're looking at 1.5$ vs 6$

Those 20-30 components he uses to build the equivalent of the LT4320 would probably cost 2.5-3$ if bought from a distributor, simply because you're ordering small quantities of a lot of different parts. He already had some of the parts before, maybe he ordered some components locally... whatever.
Then there's also the amount of space used on the circuit board... but circuit boards are cheaper these days.. the extra circuit board space is probably less than 1$, depending on where you order the board from.
[...]

--- End quote ---

well, we are dealing with facts not opinions, so let's do some fact checking...

LT4320 vs. bridge
tme Italian price (VAT excl.):
LT4320                4.73€  @ 10 pieces
400V-20A bridge   0.58€  @ 5 pieces (0.50€ @ 25 pieces)

Besides that you have to spend at least a couple of euros to get the power mosfets, so that LT4320 circuit is about 10 times more expensive than a rectifier bridge.

BTW LM393 are around 10-20 cents for 10 pieces, that is an order of magnitude even including the other needed components cost. So even accounting for the mosfet cost, Liv's circuit would be 3 times cheaper than the LT4320 one.
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