In solar power systems, Schottky diodes are used to prevent discharge of the battery during hours of darkness. Unfortunately, the voltage drop and power dissipation of a Schottky diode can be quite large when used with high wattage solar panels, thus reducing the amount of power available to charge the battery. This circuit uses the LTC4357 with a FDB3632 MOSFET to replace the Schottky diode. When the solar panel is illuminated by full sunlight, it charges the battery. A shunt regulator absorbs any excess charging current to prevent overcharging. If the forward current is greater than 25mV/RDS(ON), the MOSFET is fully enhanced and the voltage drop rises according to RDS(ON) • (I BATTERY + I LOAD). In darkness, or in the event of a short circuit across the solar panel or a component failure in the shunt regulator, the output voltage of the solar panel will be less than the battery voltage. In this case, the LTC4357 shuts off the MOSFET, so the battery will not discharge. The current drawn from the battery into the LTC4357’s OUT pin is only 7μA at 12V.
Tools & Simulations
LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.
To launch ready-to-run LTspice demonstration circuits for this part:
Step 1: Download and install LTspice on your computer.
Step 2: Click on the link in the section below to download a demonstration circuit.
Step 3: If LTspice does not automatically open after clicking the link below, you can instead run the simulation by right clicking on the link and selecting “Save Target As.” After saving the file to your computer, start LTspice and open the demonstration circuit by selecting ‘Open’ from the ‘File’ menu.