That's an interesting idea, what is you power supply, can it deliver the 20 amps, what voltage are you starting with, what out put voltage are you looking for at 20 amps? What are you going supply this power to.?
acctually i started designing the linear power supplies and chargers for pb-acid batteries for my companey and design all these using lm338 linear regulators. i used 3 regulators to make 15A power supplies and 15A chargers using approx: same design as given in application notes. the problem with these LDO regulators was that:
1) they got very heatup while passing large currents.
2)they can't conduct large current at high voltage difference between input and output. i.e; the voltage difference decrease their maximum current capability.
3) their thermal shut down property also decrease the out put voltage and current as well on heatup.
4) i had to design large PCB layouts to accomodate bulky components i.e; many 5w resistors, more than 3 large capacitors etc.
now i wana use SMPS designs to overcome all these setbacks of LDO regulators.
so i have designed a 3A power supply using lm2576 regulator and drive a 2A load successfully. now i wana proceed my work to develop 20A and greater SMPS chargers and supplies.
i have a large 34A bulky transformer with rms output equals to 36V that on rectification provide 50V across capacitors to be fed in to the regulators. and since the regulator is adjustable so it will give the outputs from nearly i think 2v to a maximum of 47V. and if i want to make a charger for 6v, 12v and 24v lead acid batteries i will have to get 7.9V, 15V and 28V outputs from the regulator (here 0.7V drop across diodes at the o/p of the charger is also take into account) thus a difference of input and output voltages will be 39.8V, 32V and 19V across the regulator.
so thats the whole story.