How does a boost converter work?

When the switch closes, current ramps through the inductor, storing energy in its magnetic field. When the switch opens, the inductor voltage reverses polarity and adds to the input voltage, forward-biasing the diode and charging the output capacitor to a voltage higher than the input. The duty cycle D determines the voltage ratio: V_out = V_in / (1-D). At D=0.5, V_out = 2x V_in.

Continuous Conduction Mode (CCM): inductor current never reaches zero during a switching cycle. Provides lower output ripple, predictable transfer function (V_out = V_in/(1-D)), and is preferred for higher power. Discontinuous Conduction Mode (DCM): inductor current reaches zero each cycle. Occurs at light loads. Easier to stabilize but higher peak currents and more output ripple.

RF system applications?

Boost converters generate bias voltages for GaAs FETs (3.3V to 5V from single Li-ion cell), gate drive voltages for GaN HEMTs (negative voltage from boost-inverter), and high-voltage supply for varactor tuning (3.3V to 30V). EMC is critical: use spread-spectrum modulation, LC input/output filters, and shielding to prevent switching harmonics from coupling into RF circuits.

Power & Thermal

Boost Converter

A Boost Converter is a DC-DC switching regulator that steps up input voltage to a higher output voltage using an inductor, MOSFET switch, diode, and output capacitor. The voltage conversion ratio is V_out = V_in/(1−D), where D is the duty cycle. Typical switching frequencies are 100 kHz to 5 MHz with efficiencies of 85-95%. Common in RF systems for generating bias voltages, gate drive, and varactor tuning from low-voltage battery or bus supplies.

Category: Power & Thermal

Efficiency: 85-95%

Understanding Boost Converters

The boost topology is one of three basic non-isolated switching converters (buck, boost, buck-boost). It is the only topology that provides output voltage higher than input without a transformer. The inductor acts as an energy storage element: charging during the switch ON period and releasing energy (at higher voltage) during the switch OFF period.

Output voltage regulation is achieved by modulating the duty cycle D via a feedback control loop. As load increases, D increases to maintain the target output voltage. The practical maximum duty cycle is about 90% due to minimum off-time requirements of the control IC.

Boost Converter Equations

V_out = V_in / (1 − D)
D = 1 − V_in/V_out

Example: 3.3 V → 12 V
D = 1 − 3.3/12 = 0.725 (72.5%)

Inductor ripple:
ΔI_L = V_in·D / (f_sw·L)

DC-DC Topology Comparison

Topology	V_out vs V_in	Ratio (CCM)	Isolation
Buck	Lower	D	No
Boost	Higher	1/(1−D)	No
Buck-Boost	Inverted	−D/(1−D)	No
Flyback	Higher/Lower	N·D/(1−D)	Yes

Common Questions

Frequently Asked Questions

How it works?

Switch ON: inductor charges. Switch OFF: inductor voltage adds to V_in. V_out=V_in/(1−D). D=0.5: 2× step-up.

CCM vs DCM?

CCM: inductor current never zero, lower ripple, predictable. DCM: current hits zero, lighter loads, easier stability.

RF applications?

GaAs bias (3.3→5V), GaN gate drive, varactor tuning (3.3→30V). Use spread-spectrum and filtering for EMC.

Related Terms

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