Background information power supply units
A switch-mode power supply (SMPS) is a power supply unit (PSU) that uses a switching regulator in order to provide the required output voltage. This regulator, for example the LM2576 step-down (buck) switching regulator, switches with a frequency of 52kHz between full-on and full-off states. The voltage regulation is provided by varying the ratio of on to off time. The high frequency of the on and off stages of the regulator minimizes energy losses and provides a high efficiency of the power supply. This high efficiency is the main advantage of a switch-mode power supply.
The ‘main’ disadvantage of a switching regulator is that it produces a high ripple and noise. For non-audio applications this ripple and noise cause no problems, but many people believe that as a result of this ripple and noise audio devices with switch-mode power supplies will never be a successful match. In our opinion this ripple and noise is only one of the problems why current switch-mode power supplies do not match with High end audio devices.
With the SBooster we focus on the enhancement of audio power supplies in general. The result is an universal solution that makes even switch-mode power supplies suitable for audio applications.
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An AC adapter is nothing more or less than an enclosed transformer. The transformer converts the mains voltage to a lower AC voltage. The conversion from AC current to DC current is internally done in the connected (Audio) device. The SBooster is not suitable for an AC adapter or AC current in general.
A passive filter is a filter that can be used to reduce the ripple and noise of a power supply. Building a passive filter is very easy, all you need is a pair of inductors and a pair of bypass capacitors. If you calculate the filter precise, you can reduce the ripple and noise in theory by 40 – 60 dB. Example: if the ripple is 50mV(p-p) and you have designed a -/- 60 dB filter you reduce the ripple with a factor 1000. This means the ripple and noise will be reduced to 50 µV(p-p).
For a linear power supply this technique will not be used, because you will need very large and expensive inductors, because the mains frequency is only 50 – 60 Hz. More effective and much cheaper is to add a linear regulator to the design. Depending on the type of regulator that is used the ripple and noise rejection will be 50 – 75dB.
Building a passive filter for a switch-mode power supply is less expensive than building one for a linear power supply. Due to the high switching frequency of 52kHz, caused by the switch-mode regulator, the size of the inductors will be considerably smaller. Because of the big difference in inductors one and the same passive filter cannot be used for both linear power supplies and switch-mode power supplies.
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