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Comment peut on comparer les technologies linéaire et à découpage ?
Size – A 50W linear power supply is typically 3 x 5 x 5.5”, whereas a 50W switched-mode unit can be as small as 2 x 3 x 0.9”. That’s a size reduction of over 90%.
Weight – A 50W linear weighs 4lbs (1.8kg); a corresponding switched-mode unit is 0.22lbs (100g) or less. As the power level increases, so does the weight. I personally remember a two-man lift needed for a 1000W linear power supply!
Input Voltage Range – A linear power supply has a very limited input range requiring that the transformer taps be changed between different countries. Normally on the specification you will see 100/120/220/230/240Vac. This is because when the input voltage drops more than 10%, the DC voltage to the shunt regulator drops too low and the power supply cannot deliver the required output voltage. At input voltages greater than 10%, too much voltage is delivered to the regulator resulting in over heating. If a piece of equipment is tested in the US and shipped to Europe, or even to Mexico in some cases, the transformer “taps” have to be manually changed. Forget to set the taps? The power supply will most certainly blow the fuse, or may well be damaged.
Most switched-mode power supplies can operate anywhere in the world (85 to 264Vac), from industrial areas in Japan to the outback of Australia without any adjustment. The switched-mode supply is also able to withstand small losses of AC power in the range of 10-20 milliseconds without affecting the outputs – a linear power supply will not. No one will care if the AC goes missing for 1/100th of a second when charging your cell phone, it will take 100 of these interruptions to delay the charge by one second. However, having your computerised equipment shutdown or reboot 100 times a day will cause a great deal of heartburn.
Efficiency – A linear power supply because of its design will normally operate at around 60% efficiency for 24V outputs, whereas a switched-mode is normally between 85% and 95%. Efficiency is a measure of how much energy the power supply wastes. This has to be removed with fans or heat sinks from the system. For a 100W output linear running at 60%, that waste would be 67W. A 100W switched-mode power supply running at 90% efficiency would be just 11W. Therefore, (67W – 11W) 56W is the extra power lost by a linear supply. Doesn’t sound much, but don’t try touching a 40W light bulb.