It is difficult to build a classic switching power supply at home. An interesting solution is the combination of a conventional low-frequency transformer with a switching voltage regulator.
Instructions
Step 1
Choose such a step-down transformer (it must be ordinary, designed for a frequency of 50 Hz) so that the voltage on its secondary winding is not less than that calculated by the following formula: Uvt = (Uout + 2) / sqrt (2), where Uvt is the voltage on the secondary winding (V), Uout - the required voltage at the output of the power supply (3, 3 or 5 V). In this case, the value of Uw * sqrt (2) should not exceed 30 V. The maximum load current of the transformer should be at least one and a half times greater than the current consumed from the power supply. Remember, however, that the proposed PSU design allows a maximum load current of 1 A.
Step 2
Calculate the rating of the fuse connected in series with the primary winding of the transformer using the following formula: Ipr = P / 220, where Ipr is the rated current of the fuse (A), P is the power of the power supply (W). In this case: P = UI, where U is the load supply voltage (V), I is the current consumed by the load (A).
Step 3
Connect to the secondary winding through a rectifier bridge capable of withstanding the load current, an electrolytic capacitor with a capacity of about 2000 μF, designed for a voltage of at least: Ufin> Uw * sqrt (2), where Ufin is the nominal voltage of the capacitor (V), Uvt is the voltage at the secondary winding (B). Observe polarity when connecting the capacitor to the bridge.
Step 4
Depending on what the output voltage of the power supply should be (3, 3 or 5 V), use a switching regulator module of type DE-SW033 or DE-SW050, respectively. Connect it in the same way as a normal 78xx series regulator, but without ceramic blocking capacitors, since such capacitors are already inside the module. Connect the positive terminal of the rectifier bridge to terminal 1 of the module, negative to terminal 2. Remove the positive pole of the stabilized voltage from terminal 3 of the module, negative - from terminal 2. If the load is sensitive to ripple arising from pulse stabilization, bypass the output, observing the polarity, with a capacitor with a capacity of 470 μF, designed for a voltage of at least 6.3 V.
Step 5
Do not install a heatsink on the module as the power generated by it is relatively small. Do not power radios operating at frequencies less than 30 MHz from this unit.
