The LM2586 and the LM3411-5 are employed here to design a fully isolated, "flyback" power supply where minimizing the parts count and simplicity is important. The LM2586 is a PWM regulator with an internal 3 Amp switch and the LM3411-5 is a precision shunt regulator acting as error amplifier plus reference. An "isolated" architecture is used in applications where the input and output power rails, grounds and feedback paths must not be directly connected but must be connected indirectly through a transformer, T1, and opto-coupler, U3, for safety purposes. Input voltage, Vin, charges up energy in the primary coil of the transformer during the on-time of the regulator switch; then, during the off-time this energy is coupled to the secondary to Vout through the diode, D1, as part of what is known as a "flyback" action. Note that the transformer here is a very easy to use off-the-shelf part. The circuit formed by DZ2 & D3 creates a switch protection circuit and R4 & C6 are set to compensate the overall control loop for best transient response. Input capacitance, C1 through C3, serve to minimize ripple effects on the input voltage, and output capacitance, C4 & C7, set the output ripple and play a part in the transient response of the power supply.
Notes: Please note that DZ2 in the schematic corresponds to D2 in the PCB layout. C8 (100nF Capacitor) can be included in the board layout.
Schematic
Example Schematic Showing Connection for all Components.
Example Schematic Showing Connection for all Components.
