CN3791 Circuit & Datasheet

Cn3791 MPPT solar charger module – Connection and Working

CN3791

If you’re working on a solar charging project, check out the CN3791—it’s designed specifically for single-cell lithium batteries, charging them reliably to 4.2V. Its standout feature is MPPT, meaning it automatically adjusts the power from your solar panel to maximize efficiency. With an input range from 4.5V to 28V, it works with nearly any solar source you have. Plus, built-in synchronous rectification means it runs cool and efficient. All you need is a resistor to set the MPPT point, keeping your circuit simple—ideal for portable solar chargers.

CN3791 Pinout

When using CN3791, make sure your VCC input line has surge protection like a TVS diode or TVR. For the SW pin, pair it with a Schottky diode, an inductor, and capacitors to build your step-up/down circuit efficiently. Set the MPPT voltage at around 76% of your input voltage—that usually hits the sweet spot. If you’re skipping temperature protection, replace the NTC pin with a fixed resistor. CHRG and FAULT pins are open-drain, so add something like a 10kΩ pull-up resistor. Lastly, don’t leave the BAT pin floating; connect it directly to the battery positive terminal.

CN3791 Equivalent

If you’re looking to replace CN3791, the CN3722 is a simplified option with fixed MPPT voltage—not ideal if you swap solar panels often. For budget or DIY projects, you can combine MT3608 with TP4056; they don’t support MPPT, but are flexible and cost-effective. However, neither option provides dynamic MPPT. For something smarter, BQ24650 is great—it supports multiple cells, dynamic MPPT, and higher current—but it’s pricier and needs more components, making it less suitable for a direct swap.

CN3791 MPPT Charging Circuit Example

In this circuit, the CN3791 chip handles your solar charging with built-in MPPT, making sure you get maximum energy from your solar panel. It clearly labels “+6V Solar Charger” at the input, stabilized by several capacitors. The chip controls MOSFET M1, combined with diode D1 and inductor L1 to step-down voltage effectively. Current sensing resistor R4 helps the chip manage the charging current. Two LEDs (green D3 and red D4) clearly show you the charging status. Battery output has filtering capacitors, ensuring smooth charging. It’s a straightforward circuit perfect for your solar charging projects.

CN3791 Lithium Battery Charger Module

CN3791 12V Battery Charging Setup

When charging a 12V lead-acid battery or series lithium batteries with CN3791, keep the input voltage between 18-24V for optimal MPPT performance. Connect the battery output directly to your 12V lead-acid battery or three lithium cells, negative side to ground. Set the cutoff voltage around 14.4V for lead-acid or 12.6V for lithium by changing the feedback resistor. The module defaults to single-cell charging, so adjust resistors accordingly. Also, choose quality inductors and Schottky diodes for stable current. If using solar panels, ensure their open-circuit voltage stays under 28V to protect the chip.