3 ms·

Power is a big deal with analog. Power wasted in heating a device is (I^2)R where I is the current through and R is the effective resistance of the device. Powe

Power is a big deal with analog. Power wasted in heating a device is (I^2)R where I is the current through and R is the effective resistance of the device. Power wasted is obviously 0 if R=0. Because I=V/R, power wasted is also 0 if R is very high (because in that case I approaches 0). Power wasted is highest if R is between 0 and "very high." This third case is where analog electronics like to live. The first two cases are where digital electronics lives. And that's why switching power supplies and Class D amplifiers are so efficient: Their effective R values spend most of the time near zero or "high" but not much time in between. This is also why even in digital circuits higher clock speed means more power: More transistor transitions between "fully on" and "fully off" mean more time spent in between in the high power dissipation regime.

KMag 6y ago
Back in the late 90s, a mechanical engineer on the MIT solar car team was explaining the latest high-efficiency motor controllers for brushless DC motors, and my degree is also in Mechanical Engineering, so this could be way off. However, as explained to me, the highest efficiency brushless DC motor controllers in the late 1990s used a phase-locked loop to get some of the off periods in the square wave in the power conversion stage to be in sync with the switches between coils in the motor. Transistors don't switch instantly, and a good deal of your power loss is during the transition between fully off and fully on. By synchronizing the two parts of the motor controller, you get the coil changes to happen when that part of the controller is seeing dips in its power input, so you get less loss.