The LM5020 is employed here to design a SEPIC power supply where the positive input voltage rail can range above or below the positive output voltage rail. The LM5020 is a PWM controller that drives an external N-FET switch, M1. During start-up the switch is powered through its own internal startup regulator at the Vin pin. During normal operation it is powered at the Vcc pin via the small LM2951 regulator as a source of less widely varying voltage. Typically, the SEPIC architecture is used to take advantage of easily available inductors rather than less available transformers used in flyback architectures. During the on-time of the switch the input voltage, Vin, charges the L1 inductor. The negative voltage, relative to ground, across the sepic capacitor, C10 & C11, charges the inductor L2. During the switch off-time both inductors discharge through D1 to the output. It is the average of this pulsed discharge current that forms the output load current while also charging the output capacitors, C12,21,13, to the required output voltage. Current mode operation senses current at R19. Transient compensation is optimized via the resistor and capacitor circuit along the feedback path from the output to the VFB and COMP pins of the IC.
Schematic
Example Schematic Showing Connection for all Components.
Example Schematic Showing Connection for all Components.
