some tricks on simple line supply DC/DC converters

Maybe you will be interested in ideas which I have been working on. I use the simple differentiation approach in something I have called the USMPS, U standing for universal. It enabled me to come up with a single approach of which I use various modifications in almost all of my designs. I do it all for my personal projects, non-commercial and non-profit (for me so far based on my present interests)--a hobby, but with the purpose to help others a well as myself.

I find that using differentation rather integration gives much more robust stability and fine control of the PWM, especially at narrow pulse widths. I use the 74C14 (CD40106B) and the IR2110, 2112, or 2113 in almost all my projects. My present project is a battery charger/brushed motor controller for my e-bike project which uses the same transformer to power the motor and charge the battery. My next project is an inductive heater to apply to a water pipe. I have a design for a ZVS PFC which is based on the ZVS USMPS. (ZVS= zero voltage switching. I have also used the USMPS in ZCS mode.

http://tech.groups.yahoo.com/group/switchmode/

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Great!!! SMPS up 50KW???. It is the subject of my interest.I have converted some ATX supplies in to Fix/ Varialble bench power supplies. I want to make Battery charger in CC mode out of old PC ATX power supply. can you please help me?. Secondly I am not able to get High frequency Ferriete cores for various experiments. Hence I want to use toroid cores of out put filters, that I have reclaimed from various old PSUs, for making SMPS transformer. Can you help me how to calculate number of turns/ wire guage etc? For example: I want to convert ATX 250W PC power supply (TL 494/ SG 3525) into 5V 50A (or 40A) then, what should be the size of Torid? can I use existing out put choke toroid to make the required transformer? if yes, then what is the required wire guage and number of turns? I will take the pain of winding mannually. I have made one PSU by paralleling two SMPS to make 4 to 5.6V variable 50 A (CV) supply, that weighs less than 1.5 Kgs.

First,all is based upon Maxwell Laws,and a knowledge of basic equations is sufficient.
Ferrites are commonly used to 100kHz,some new ones to 2MHz.Their Magnetic Induction at saturation is about 3500Gauss(0,35 Tesla).
Iron or Iron-Nickel alloys are used at lower frequencies,but may be used at hundred of kilohertz if1)their are finely laminated(below 25µ thickness strips)

2)they are amorpheous(roller vitrified,as common aluminum foil).A vitrified material achieves twice the resistivity of the same cristallized metal,due to more lattice scatterring.Hence,half eddy currents,and twice the peak power

Then,you use:rotE =-dB/dt and rotH=j

with B=µ°H(air)=µ°µrH(iron)

V=-dPhi/dt with Phi=nBs

where Phi is the flux in the core,n is the number of turns,s the section of the core.
With µ°=4PiE-7 Henry/meter,all is in S.I. units,not CGS.

dPhi=nsdB;where dB is the induction swing from -0,35T to +0,35T,hence 0,70T

dt is the time to induction swing,hence half the period.At 100kHz:dt=5µs

And using the integral form of Ampere's Law rotH=j,you integrate as:

H(air)l(air)+H(iron)l(iron)=nI

where H(air) and H(iron)are related to B(see above),l(air)is the gap(which may be zero,although there exist distributed gap toroïds)and l(iron)the length of a flux line,simply the mean circonference of the toroïd.
Then,the transmitted power is:P=[V(max)I(max)/2]F where F is the frequency.
If this is not clear enough,I shall give an example later.
Let's say that 5 ferrites EE of 100x57x25mm transmit 20kW at 40kHz.
Common practive in the industry.
You may scale up or down accordingly.

Thanks for comments. I am trying some PSUs for battery charging so that the rural folk use them to beat energy crises. I have tried to convert 40 W electronic ballast in to portable SMPS with little success. In India (may be elsewhere also) consumer electronics are very cheap due to mass production techniques. Say ATX PSU cost US$: 4 to 6 in India and if ask for 5V 10 amps PSU that takes 85 to 270 VAC 40 to 60 Hz; then it is available for not less than US$: 160

I am more pactical oriented. I believe only if I see it working, not on paper. If any one of you tried to covert Florocent Electronic lamp ballast in to smal power supply , please share... An electronics ballast in India costs less than US$ 2 in India.

I am more interested in using toroid as SMPS transformer. I shall try one as guided by one of our friends.

meet again, bye.