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the fundamental behind the most of SMPSes are the same but the advances in technology provide lower cost, efficient and feature rich chips which integrate all of the power electronincs circuits in a single die or package (hybrids).
currently several manufacturers provide integrated switchers/regulators with this range of power or upper; BTW the circuit is useful as a home made DC to DC convertor.
This 'simple' step down converter is one of the most expensive I ever seen. (1977 it's ok, but today too expensive)
This regulator has a poor efficiency. I think the losses in the switching Darlington transistor are > 10W. So you are in need to cool it well with a very expensive and BIG heat sink !!! A mechanical disaster.
Modern concepts are much cheaper. They work with MOSFETs and do not need heatsinks to be cooled.
8) i have used 555 timer in low power DC DC converter application, works fine but has many limitations. 1; have to add external referances 2: add external drive elements 3: limited sypply voltage range. 4:external components required for current limiting .
way back in 77 the price of SMPS controllers where high and people where experimenting using other available IC s.
but now the price of 555 , SG3524, TL494 or UC 3842 are almost equal. there is no point in designing using Timer IC.
I don't know why people think its shame to use old or cheap stuff to acomplish a job, the guy just wanted to share a nice circuit, in deed, the UC3843 is not available in my country, so Such people like me will consider such circuit of great help.
Anyway,ITS UP TO THE CONSTRUCTOR whether to use new, old or even discontinued products. My self, I have used the µPC1225H to build an audio power amplifier of 60 watts output. Its performance was great, although its a continued one and really old one.