emcoscilloscopeswitch-mode-power-supply
I'm wondering why digital oscilloscopes are using switching power supplies instead of linear power supplies.
The SMPS has a higher efficiency, but it can produce some noise during high frequency switching (PWM) and also EMI that can affect the signal shown on the display.
I'd firstly agree with other posters as to economics of scale. Consumer devices are produced in the millions whereas such a market does not exist for digital oscilloscopes.
Secondly, oscilloscopes are precision devices. They need to undergo rigorous quality control to ensure they live up to expected standards. This further increases costs.
As for bandwidth. The Nyquist criterion states that the sampling rate should be at least twice the frequency you want to measure. But even at twice the rate, it is terrible at best. Consider the following pictures:
The graph captions tell the story. You need to exceed the specified bandwidth by a great amount in order to gain an accurate representation of the square wave input signal (high frequency harmonics). And greater bandwidth = greater cost.
In the end the precision, bandwidth and limited production quantities that drive up prices.
The answer to which one you use depends on the application, and the efficiency needs.
For example, you're asked to make a phone charging dock. The dock is powered via a 12 V wallwart, and powers the phone with 5V of power at 500mA. Using a linear regulator, 3.5W is dissipated.That's quite a bit of waste, but you're connected to the mains, and a charging dock is a big enough device, where a properly heat sunk regulator wouldn't cause a lot of heating issues.
On the flip side, suppose you're building a wearable device that operates on a small Li-Po battery, even if you designed a LDO circuit that only wastes about 1W of power, a switching circuit would be more desirable as if designed properly, you could reduce your wastage to <10% that of the linear regulator
Note: Pay attention to the efficiency curves of switching regulators. They normally only have high efficiency for small ranges of current usage, and it helps to understand what current usage your application operates on in different condition to design the most efficient power circuit. Also - laying out swtiching regulators on a PCB can be hit/miss - I've seen a lot of incidents where tiny layout issues can mess with the desired voltage out.
Best Answer
The SMPS advantages over linear supplies, of compactness, high efficiency so low heating, light weight and wide input voltage range, are very valuable in portable equipment like an oscilloscope.
The principle disadvantages of SMPS over linear supplies are switching noise on the output and radiated EMI.
(Circuit complexity used to be considered another but not nowadays.)
Well-designed output filtering can reliably reduce ('remove') this noise and an oscilloscope carries a high enough cost to afford it.