The design incorporates an external soft-start circuit to extend the soft-start time and ensure that the solar panel does not become overloaded during turn-on

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• Article «Solar panel powers two-stage lead-acid battery charger»
• Figure 1. A solar cell's current output decreases with a reduction in sunlight
• Figure 2. A solar cell's output voltage decreases with an increase in temperature
• Figure 3. The solar charger system uses an 18-cell, 3 W solar panel as the input source. The system comprises two stages, in which the first stage monitors the solar panel's voltages using a SEPIC topology and provides the output voltage, which tracks the input of
• Figure 4. A SEPIC is a dc/dc topology that allows the output voltage to be greater than, less than, or equal to the input voltage
• Figure 5. Replacing the inductor L₂ of Figure 4 yields an isolated SEPIC
• Figure 6. The design incorporates an external soft-start circuit to extend the soft-start time and ensure that the solar panel does not become overloaded during turn-on
• Figure 7. Changing the value of R_B adjusts the SEPIC voltage's setpoint to accommodate different solar panels' voltages. You can adjust a resistor divider comprising R_T and R_B to match the SEPIC's reference voltage, typically 1.34 V
• Figure 8. The second stage comprises a SEPIC that operates in boost mode with constant current-charge control and charges the 12 V battery
• Figure 9. The R_BR/R_TR divider that connects to the LM4041 in the first stage senses the solar panel's output voltage, which initiates a restart mode by disabling the second stage of the circuit by pulling down on the enable pin of LM5001
• Figure 10. The normal operating temperature for the charger is 60 °C
• Figure 11. Efficiency falls off rapidly when the input voltage from the solar panel falls below 6.5 V