EMC Question of the Week: March 19, 2018
Increasing the switching frequency of a switch-mode power converter,
- reduces the losses in the switch
- generally reduces the electric-field coupling from the converter
- generally produces a smoother output voltage
- all of the above
Answer
The best answer is "c." The first choice is clearly incorrect, because switching losses tend to be proportional to the switching frequency. Most of the power dissipated in the switching device is dissipated while transitioning from on-to-off or off-to-on. The more often the switch changes state, the more power is lost. The second choice is also incorrect, because electric-field coupling from electrically small devices/heatsinks tends to be proportional to frequency. If "a" and "b" are incorrect, then "d" must also be incorrect.
The only choice that one can make a reasonable argument for is "c". At lower switching frequencies, the output voltage will tend to vary more from one switching cycle to the next. Switching at higher frequencies allows the converter to respond to variations in the output voltage more quickly, which helps to produce a smoother output voltage.
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