That can be a lot of heat to get rid of in a small and sealed plastic package. Even at only 500 mA output (half its maximum capability), it would dissipate 1.3 W at minimimum. Over 80% efficient is "easy", 90% efficient reasonably attainable in a lot of mainstream circumstances, and close to 95% attainable when need be and efficiency is a prime priority. Electronic components have advanced considerably since the caveman days, so today it's generally cheaper and smaller to make the power supply more efficient than to add the ability to dissipate a lot of heat. The strive for efficiency is actually not so much to not waste the power, but to not have to get rid of the heat from wasting the power. Today there is much more pressure to make power supplies small, light, cheap, and sometimes efficient. It didn't matter much that the linear regulator needed over 2 V headroom since there had to be significant slop built into the raw unregulated supply for various other reasons anyway. To get a regulated supply, they'd follow that with a linear regulator. Since it's output is 5 V, that means its input needs to be at least 7.5 V else the output being 5 V is not guaranteed.īack in neolithic times, cavemen would make a power supply by using a big-iron transformer to drop the line voltage, 4 diodes to take the absolute value, and a cap to smooth it out. This parameter is often referred to as the headroom or dropout voltage. One parameter of a linear regulator is how low the input voltage can go while it can still control the output voltage within spec. Electronic regulators use transistors for much the same purpose. In that case there is a real valve inside that is opened more or closed more so that the output pressure is maintained. The concept is the same as a mechanical pressure regulator. These type of regulators are totally powered from the input voltage, and adjust how much current they allow to pass from the input to the output. This means they take a high and varying voltage in, and produce a low and steady ("regulated") voltage out. The difference is due to the strongest force in the universe: Marketing.īoth devices are linear regulators.
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