Cool 5V stabilized power supply.
A 5V Switching Mode Power Supply (SMPS), replaces a 7805 (= linear 5V stabiliser).
In applications with e.g. a PIC, an SD/MMC card reader, an Ethernet interface based on the ENC28J60 and an RS232 interface based on the Max232, the current drawn from the 5V power stabiliser becomes rather high. A heat sink is required for the stabiliser IC (usually an 7805, fed from an transformer via a bridge rectifier and a buffer elco). Things get worse if more components are added to the circuit: the heatsink must become bigger and bigger. Of course one can take a number of mesures to make the input voltage of the 7805 as low as possible (but not too low: stabilisation must still be possible), but even then the dissipation problem persists.
This circuit poses a solution to that problem.
This type of power supply has the following characteristics:
The main components in the circuit are:
- The circuit is more complex than the 7805, but dissipates much less power: The stabilising circuit stays much cooler, as is the rectifier and the supply's transformer. In most cases no heat sink on the IC itself is required (even with 1A drawn from the supply).
- The output voltage is somewhat less stable (more variation, more ripple) than the one of the 7805, but well within boundaries for e.g. PIC supply.
There are also versions of the LM2575 for other output voltages (o.a. 3.3V).
- The IC (IC1) that does the actual work (switching and stabilising): LM2575-5.0 (National Semiconductor)
- The coil L1, should be approx. 200uH and capable of having the 1A output current.
- The diode D1, a schottky diode capable of having 1A, 30V
- Capacitor C2, which is together with L1 the output filter.
- Finally, components that are also present in a normal 7805 supply: the rectifier B1 and its capacitor C1.