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Why I Prefer Power MOSFETsPower MOSFETs began their use in commercial audio amplifiers in = the=20 late Seventies when so-called lateral power MOSFETs became = available=20 primarily by Hitachi. The most well-known of these early power = MOSFET=20 amplifiers were the Hafler designs. Then around 1980 = International=20 Rectifier came out with the legendary HEXFET vertical power = MOSFETs. These=20 were initially aimed primarily at switching power supply and = other power=20 control applications, and so some audiophiles mistakenly = overlooked them=20 as good candidates for audio power amplifier output stages. The = HEXFETs=20 were distinguished by the application of well-developed and = sophisticated=20 fabrication techniques borrowed from the MOS integrated circuit = industry.=20 Think of a Power MOSFET as about 1 million very fast little MOS=20 transistors connected in parallel with an extremely efficient=20 metallization technology that keeps resistance down and helps to = get out=20 the heat.=20 In the early Eighties, I designed a MOSFET power amplifier = using the=20 HEXFETs which dealt with and overcame the drawbacks in certain = areas that=20 MOSFETs had with respect to bipolar transistors, while = capitalizing on the=20 many advantages of the MOSFETs. Among other improvements, this = amplifier=20 was the first to apply the Hawksford error correction scheme to = MOSFET=20 power amplifiers, solving the so-called transconductance droop = problem.=20 The design was published as a paper in the Journal of the Audio=20 Engineering Society and is available elsewhere on this site.=20 The most significant advantages of power MOSFETs, particularly = vertical=20 ones are:=20
Chapter 11 in Designing Audio Power=20 Amplifiers is dedicated to the design of MOSFET power = amplifiers.=20 MOSFETs are not without their own shortcomings and design = challenges, and=20 those are discussed as well. = |