Boost Converter 5V DC Input – 12V DC Output

This project describes a compact boost converter circuit that steps up a 5V DC input to a 12V DC output, utilizing the LM2733 switching regulator. The design emphasizes high power density through the use of the small SOT-23 package, minimal inductor and capacitor sizes, and high switching frequencies 1.6 MHz. Protection is provided through cycle-by-cycle current limiting and thermal shutdown. Internal compensation simplifies design and reduces component count.

Key Features

• Input Voltage: 5V DC
• Output Voltage: 12V DC
• Max Load Current: 330mA
• Switching Frequencies: 1.6 MHz (X)
• Cycle-by-cycle current limiting for safety and reliability
• Compact design with tiny capacitors and inductors for space efficiency
• PCB Dimensions 16.67 x 5.08 mm

Design Insights

• The LM2733’s internal switch, capable of handling up to 1A, contributes to the minimal power loss.
• The small inductor and capacitors contribute to the high-power density, making the circuit suitable for space-constrained applications.
• The high switching frequency allows for smaller passive components, reducing overall size.

Potential Applications

• Portable electronics requiring a 12V supply from a 5V source
• Compact power supply modules
• Embedded systems with space and weight constraints

Connections

• Pin 1 = Power Input 5V DC, Pin 2 = GND, Pin 3 = Output 12V DC

The LM2733 device is a switching converter IC that operates at a fixed frequency (0.6 or 1.6 MHz) using current mode control for fast transient response over a wide input voltage range and incorporate pulse-by-pulse current limiting protection. Because this is current mode control, a 50 mΩ sense resistor in series with the switch FET is used to provide a voltage (which is proportional to the FET current) to both the input of the pulse width modulation (PWM) comparator and the current limit amplifier. At the beginning of each cycle, the S-R latch turns on the FET. As the current through the FET increases, a voltage (proportional to this current) is summed with the ramp coming from the ramp generator and then fed into the input of the PWM comparator. When this voltage exceeds the voltage on the other input (coming from the Gm amplifier), the latch resets and turns the FET off. Since the signal coming from the Gm amplifier is derived from the feedback (which samples the voltage at the output), the action of the PWM comparator constantly sets the correct peak current through the FET to keep the output voltage in regulation. Q1 and Q2 along with R3- R6 form a bandgap voltage reference used by the IC to hold the output in regulation. The currents flowing through Q1 and Q2 will be equal, and the feedback loop will adjust the regulated output to maintain this. Because of this, the regulated output is always maintained at a voltage level equal to the voltage at the FB node “multiplied up” by the ratio of the output resistive divider. The current limit comparator feeds directly into the flip-flop, that drives the switch FET. If the FET current reaches the limit threshold, the FET is turned off and the cycle terminated until the next clock pulse. The current limit input terminates the pulse regardless of the status of the output of the PWM comparator.

Schematic

Parts List

Block Diagram

Connections

Gerber View

Photos

LM2733 Datasheet