When is a power supply regulated?

Answer 1

Mostly when we use electronic equipment that operate with digital circuits, signals, audio and in fact most consumer electronic devices require a smooth and stable source of supply to eliminate electronic noise and to ensure precision for voltage levels.

The traditional power supply would use a transformer to step-down the AC voltage, then convert it to a DC by using a rectifier circuit. The DC which consist out of the ripple of the original AC which will required to be smoothed with a ripple filter capacitor. This will smooth the DC to look almost like the output voltage of a battery.

By this stage the voltage is usable for many robust applications. However for most consumer electronics the filtering of the capacitor is not good enough to ensure a stable and smooth DC. Most modern microchips have very exact specifications which a power supply must comply too. Any ripple or fluctuation outside these limits will cause failure of the device or cause unwanted noise.

Therefore a circuit as simple as a resister and a zener diode can be used to regulate the voltage. This will mean that the voltage from the ripple filter stage will be reduced to a voltage lower than the lowest meaningful instantaneous voltage of the filtered voltage. Then all the voltage lower or equal to the regulated voltage will be passed while everything higher will be absorbed in some form of resistance for linear devices.

This regulator function would in most practical applications be in the form of an IC and often a heat sink is connected to it to deal with the dissipated power. This IC can also come in various technologies. For light current applications linear technology is popular since linear is known to have poor energy efficiency, but it forms a very cost effective solution, simple, compact and reliable. Switch mode technology becomes more energy efficient for higher currents and it has excellent efficiency which also allows it to consume very little energy and reduce the amount of heat which is produced. This type of technology has made high power applications such as battery chargers or amplifiers more compact and more cost effective when employed.

Some applications might even prefer to use dc-dc converters to isolate supply rails from others and have regulars built in.

Even transformerless technology, such as computer power supplies will at the last stage employ some form of regulator technology before presenting the supply voltage to the functional circuits.

The voltage regulator will for all theoretical purposes form the last functional stage of a power supply before a very stable and low noise output DC voltage is supplied, positive or negative.