Linear voltage regulators are probably the most famous ICs. It is very easy to use them, they are cheap enough, and can be found in every store with electronics. However there are a lot of limitations in their use and they have low performance. Input voltage must be at least 3V more (drop out voltage) than the name output regulated voltage, but it must not be too high because of the rejected thermal power. For example, if we use a 5V regulator (LM7805) and the input voltage is 25V, then the drop out voltage is 20V. For 500mA consumption the rejected thermal power is P=20x0.5=10W and for 4 days continuous operation will cost us 1kWh more. Even more, the performance of the power supply becomes lower than 20%. A heat sink is necessary as well, and must care for nice air flow.

      This loss can be limited with switching power supplies. They produce short pulses to their output direct to a low pass filter and finally remain only DC component. By changing the duration of the pulses DC voltage can be adjusted. With a feed back present output voltage can be stabilized. The performance of this power supply is more than 80% because the switching element works either in saturation or in cut-off region, so there is no thermal power rejection from this and in most applications a heat sink is not necessary. Modern switching power supplies consist of only one IC and 3 elements: a diode, an inductor and a capacitor and thus is very easy to use them.

      By using the proper connection we can replace a linear regulator with a switching one (if we fit the diode and the inductor round the IC). In the following pictures a simple method is presented in order to make a module with LM2576-XX and put it in the place of LM78XX.

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