500w smps dadasheet
Hi,
Be very careful about replacing any components in an established SMPS design I totally agree with melc about the TLC431, these are readily available and the only type of component that you should use in the configuration shown.
Regarding output power 70W might be achievable with the circuit shown as melc said. The switching FET will give about 5A continous output current with average heatsinking, this is pulsed so the pulses could be a bit higher as per the device datasheet.
Increasing the power is a bit more complicated than just upping the wire guage, the size of the core is important too and increasing the wire size only works up to a point because of the skin effect. This means that only the outer skin of a wire is carrying current at the high switching frequencies. This is worked around by using several strands of smaller insulated wire in parallel to make up the required current carrying capacity, use wire of about 0.3mm dia or less and as many strands as you need to carry the pulse currents (the books still talk about using Litz wire for this purpose - if you can get it!) design the wire size based on about 3 - 5A per square mm (US designers use 400 to 1000 circular mill per A) (a lower current density means it runs cooler on full load). Designing the magnetic components is OK if you are reasonably up to speed with magnetics but the terminology can seem a little daunting at first, follow the design advice of the manufacturers of the core materials and you will be OK, do not try to be a hero (just yet) and use the material outside its recommended limits, there are cases when this is done but only do it when you know the reasons why. There is a lot of info on this available on the web and books are available, my favourite is Practical Switching Power Supply Design by Marty Brown of Motorola Inc. Use a spreasheet or Mathcad to design the magnetics etc. You can design everything this way and have the whole set of of the design calculations on the sheet. which is very useful for the next design you do, you can just copy it and edit the new version, this will save hours.
Have a look at the website of your chosen magnetics manufacturer, (Ferroxcube, Fair-rite, Magnetics Inc, Siemens etc) most of them have app notes or even design software you can download to enable you to design the transformer / inductors, make sure you can easily get the recommended cores locally in small numbers before committing to a design incidentally). Increasing the output power much above 100W normally requires a diffierent topology to the flyback that is normally used for isolated low power SMPS (Half bridge Forward topology converers are good to about 500W, Full bridge designs for higher powers).
As you probably realise the design of SMPS are tricky but there is no reason why you should not succede if you follow it through logically. The use of design calculations are very important for a SMPS, do not try to design one by guesswork, modifying an existing design unless it it a very minor mod, often even what seems like very minor mods can have a disasterous effect on a design's validity. I have designed a number of these over the last few years and I still often need to teak the design slightly at prototype stage so don't worry if you need to try twice. Be ready to switch off quicky if it smokes, usually though you dont get time because the FET blows first and usually manages to protect the main fuse even if it is of the correct value if anything is seriously wrong with the design / build!
ONE SERIOUS WORD OF CAUTION - THIS IS A MAINS POWERED SMPS WHICH USES DIRECT RECTIFIED UN-ISOLATED MAINS POWER - TREAT IT WITH EXTREME CAUTION WHEN DEBUGGING IT. THE USE OF A 1:1 ISOLATION TRANSFORMER WITH THE SECONDARY GROUNDED AT ONE END MAY BE WORTH CONSIDERING FOR THE DEBUG STAGE. This will not prevent a shock if you touch the wrong place but it may make it less likely to be lethal.
Good luck
Bob.