The LM5000 is used to design a SEPIC power supply with a positive input voltage rail that can go above or below output voltage rail. The LM5000 is a PWM regulator with internal FET switch which minimizes parts count and simplifies design. Typically the SEPIC architecture is used in order to take advantage of easily available inductors rather than less available transformers used for similar applications with flyback architecture.
During the ON-time of the switch the input voltage charges the L1 inductor. The negative voltage, relative to ground, across the SEPIC capacitor Cs 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 and charges the output capacitors to the required voltage. Capacitor Css controls the softstart time and Cbp is used for bypassing purposes. Minimal ceramic capacitance, Cin1 and Cin2, is required on the input, while output capacitance is typically larger (Co2 is 470uF) due to the pulsed nature of the output current waveform. Transient compensation for the power supply loop is accomplished via the resistor and capacitor combination at the COMP pin of the regulator.
Schematic
Example Schematic Showing Connection for all Components.
Example Schematic Showing Connection for all Components.
