Background information power supply units
Linear power supplies are available in two versions: an unregulated and a regulated version.
An unregulated linear power supply uses a transformer to convert the mains voltage to a lower voltage. A rectifier bridge converts the lower AC voltage into a DC voltage and a capacitor with high capacity smoothes the pulsating current from the rectifier. However some periodic deviations from the smoothened direct current will remain, which is known as ripple and noise. These pulsations occur at a frequency related to the AC power frequency multiplied by two and a ripple of 5-15% of the output voltage is common.
An unregulated linear power supply is the most easy power supply to design and build. The DC output Voltage is not stabilized and the output voltage drops if the current of the load rises. Example; a 5V – 1A PSU has an output voltage of 8V with no load, 5V with full load (1A) and 6,5V with a 0.5A load.
The combination of the extreme high ripple and noise and the unstable output voltage makes this type of PSU unsuited for high quality Audio applications and cannot be used in combination with the SBooster.
The main difference between a regulated and an unregulated linear power supply is that the output voltage is fixed. In general the basic ingredients of both versions are the same: a transformer, a rectifier bridge, a smoothing capacitor, but additional a linear regulator is added to the design to stabilize and adjust the voltage. This regulator will also reduce the ripple and noise in the output voltage. This is also the biggest difference compared with a switch-mode regulator, which causes ripple and noise.
There are different methods to stabilize the voltage. The most common method is to use a three-terminal positive voltage regulator. If the regulator needs 1.3V or less to operate, we call the regulator a LDO, low dropout, regulator. Popular but-old fashioned types that you can find in audio devices and PSU’s are the LM317 and LM780XX. Each renowned company that currently offers high-quality PSU’s uses a LX1086, or LX1085 LDO regulator.
The regulators can be found by a variety of brands and specifications. It is therefore important that the exact brand and type are selected. The choice is significant because it can make the difference between a “just good” sounding to a “superb” sounding power supply.
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