When you push noise that far down, it becomes inconsequential to most circuits, which is why linear regulators are still used, despite their inefficiency. I've tried to come up with an example of a device that would run poorly because of that fuzz, but nothing comes to mind. That means a bit of input bumpiness is going to come out of the filtering and regulation stages as just a bit of fuzz. The other major type of power supply regulation is the linear regulator, which typically suppresses low-frequency input noise and ripple by 80-100 dB. Switchers do much nastier things to the power than put some bumps on the input sine wave, so they already have to have a lot of filtering if the load circuit requires clean power.⁴ The most common sort of power supply used for modern electronic devices is the switched-mode power supply. All that matters to such a device is that it gets sufficient RMS power and that the power is within the device's input voltage limits.³ Power Supply Typesĭevices with strong power supply filtering and regulation generally don't care about the nonidealities in a modified sine wave. While I wouldn't worry too much about what poor power quality would do to an electric drill, there are motor-driven devices I wouldn't want to run from a poor-quality UPS, such as a CPAP machine.Īs to the question of whether any of the equipment in your SOHO rack cares about the quality of the UPS power output, that depends on the design of each component's power supply. The steps on the output of a modified sine wave are in the hundreds of Hz region, so a modified-sine UPS is likely to cause a change in the way the motor runs that you can actually hear. Voltage that doesn't increase and decrease smoothly will cause variations in speed. Dirty power shows up as a portion of the output signal, depending on how much feedback the amplifier has.¹ This is one of the two main causes of line hum in old amps.²Īnother example of a circuit where power quality may affect device operation is something with an AC motor, such as a corded electric drill, where the speed of the motor is a direct function of the voltage put across it. Linear regulation throws off too much heat to be practical in such a device, low-noise switching regulation technology wasn't really available at the time, and so amps of that time were designed with basically unregulated power directly driving the amplification stages. Devices That Care About AC Power QualityĪ classic example of a device that starts with such an assumption is an analog audio power amplifier designed in or before the early 1970s, or a more modern piece designed along the same lines. Clean AC is ubiquitous, so some electrical devices are designed with it as a starting assumption.
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