Switch Mode Power Supply Design
Fast switching power supplies have been with us for possibly a hundred years but it’s only now recently that these power supplies are starting to become very popular as design trends have made them more reliable and cost effective than every before. With the high prices of copper and steel it’s no wonder that the old linear power supply is losing popularity. Shipping charges, based on weight or volumentric weight also plays a role and manufacturers know this. A very large factor in home theater failure is the overloaded poor mains transformer which is not designed in many budget systems to continuously power loudspeaker loads with a music source. Either the thermal trip goes faulty or the primary winding eventually shorts out burning the mains fuse. Switched mode power supplies have become more resilient, generating far lower electromagnetic interference (EMI) and general noise and they can be mass produced at a fraction of the cost of a mains 50Hz/60Hz transformer. Looking back the only things that haven’t changed in modern equipment is the loudspeaker and mains transformer, both very ineffecient devices.
Switch Mode – the first, literally…
The first known fast switched supply was the vibrator power supply which worked very much like a bell circuit. These were used in motor car audio where the +B for the tubes/valves required a step up from +12V auto supply to +300V after being rectified. Motor alternators were also popular where the motor was often driven from 3 phase, stepping up the voltage to designed output through an alternator. This was often a high frequency output – in some cases the output was DC to be used as a welder for instance.
Static inverters were very common in the 60s and 70s – these would have been the fore-runner to the modern SMPS although for all intents and purposes they were SMPS, just known by another name like chopper power supplies or switchers.
The intention of the article is not to re-invent the wheel but rather put the reader on to websites where the authors or forum administrators have one specific goal – to educate the reader and in many (most) cases assist the DIYer to manufacture their own SMPS.
Most websites dedicated to SMPS design have users ether trying to build or purchase power supplies to power their audio equipment, welding stations or inductance heating. We have already dedicated a page or two to inductance heating so in this article we will focus on design in general.