How can a tiny boost chip turn a 3.7V lithium battery into 5V, 9V, or even 12V? It doesn’t create energy—it cleverly stores and releases energy using an inductor and fast switching, leveraging fundamental physics to “pump” voltage upward.
A boost converter consists of four key parts: a switch (MOSFET), a diode (or synchronous switch), an inductor, and an output capacitor, all controlled by the IC. Operation cycles through two phases:
Phase 1: Switch ON – Inductor Stores Energy
When the internal MOSFET turns on, input voltage is applied across the inductor. Current ramps up linearly (since V = L·di/dt), and energy is stored in the inductor’s magnetic field. During this time, the output capacitor alone powers the load.
Phase 2: Switch OFF – Inductor Releases Energy
When the MOSFET turns off, the inductor resists the sudden current drop by reversing its voltage polarity. This “kickback” voltage adds to the input voltage, creating a total voltage higher than Vin. Current now flows through the diode (or synchronous MOSFET) to recharge the output capacitor and power the load—resulting in Vout > Vin.
This cycle repeats at high frequency (typically 100 kHz–2 MHz). The duty cycle (D = on-time / total period) sets the voltage gain. The ideal equation is:
Modern chips include a feedback loop: a resistor divider samples Vout, compares it to a reference, and adjusts D in real time to maintain regulation—even as battery voltage drops or load changes.
Synchronous rectification replaces the diode with a second MOSFET, slashing conduction losses and pushing efficiency above 90%. Features like soft-start and over-current protection enhance reliability.
Crucially, boosting voltage doesn’t save power—output power is always less than input due to losses. But since P = V×I, higher voltage means lower output current, making boost converters ideal for powering USB devices, LED strings, or sensors from low-voltage batteries.
In essence, a boost chip acts like an “electronic water pump,” using the inductor’s inertia and precise switching to lift voltage—enabling compact, efficient power delivery in today’s portable electronics.
