Description
In integrated circuits (ICs), the buck DC-DC converter and the boost DC-DC converter are two common switching power supply topologies used to efficiently regulate voltage.
1. Buck DC-DC Converter Definition
The voltage regulator converter is a switching power supply circuit that reduces the input voltage ((V_{in})) to a lower output voltage ((V_{out}), where (V_{out} < V_{in})). Its core achieves voltage conversion through high-frequency switching (MOSFET) and energy storage and release by inductors and capacitors.
Working principle
●Switching stage: When the switch is conducting, the input voltage passes through the inductor and capacitor to supply power to the load, and the inductor stores energy.
●Off stage: When the switch is turned off, the inductor releases energy, and the output voltage is reduced by maintaining the load current through the rectifier diode (or synchronous rectifier tube).
●Regulation method: The duty cycle (D) of the switch is controlled by pulse width modulation (PWM).
Key features
●High efficiency (typically > 90%);
●Small output current ripple;
●Requires an output filter circuit (LC filter).
Typical applications
●Processor/FPGA power supply: Convert 12V/5V to 1.2V, 3.3V, etc. low-voltage power supplies.
●Battery-powered devices: For example, lithium batteries (3.7V) in mobile phones and tablets, reduce the voltage to 1.8V for chip use.
●Industrial systems: Convert 24V to 5V or 3.3V for sensors, MCUs, etc.
2. Boost Converter (High Voltage DC-DC Converter) Definition
The boost converter raises the input voltage ((V_{in})) to a higher output voltage ((V_{out}), where (V_{out} > V_{in})), achieving the voltage increase through the storage and release of energy in an inductor.
Working principle
●Switching stage: When the switch is on, the inductor charges up, and the current increases linearly. The load is powered by the output capacitor.
●Off stage: When the switch is off, the inductor voltage is superimposed with the input voltage, and it supplies power to the load and the capacitor through a diode, causing the output voltage to increase.
●Regulation method:.
Key features
●The output voltage is higher than the input voltage;
●The input current is continuous, but the output ripple is large;
●Pay attention to the withstand voltage of the switching transistor (due to the high output voltage).
Typical applications
●Battery-powered devices: such as a single lithium cell (3.7V) boosting to 5V for a USB device.
●LED driving: boosting to tens of volts to drive LED strings.
●Automotive electronics: 12V boosting to 48V for a hybrid power system.
●Energy harvesting: boosting from the low-voltage output of a solar panel or thermocouple to a usable voltage.
3. Comparison between Voltage Reduction and Voltage Boost Converters
Characteristics Voltage Reduction (Buck) Voltage Boost (Boost)
Voltage Relationship (V_out < V_in) (V_out > V_in)
Efficiency Usually higher (>90%) Slightly lower (85% - 95%)
Topology Complexity Simpler Requires higher voltage-resistant components
Typical Applications Low-voltage power supply, digital IC Battery boost, LED driving, high-voltage demand
4. Other Derived Topologies
● Buck-Boost: Adjustable voltage conversion (such as TPS630xx series), suitable for scenarios with large input voltage fluctuations (such as battery discharge process).
● SEPIC/Cuk: Supports more flexible input-output relationships, but is more complex.
5. Selection Considerations
● Input/Output Voltage Range;
● Load Current Requirements;
● Efficiency and Heat Dissipation Requirements;
● Size and Cost (such as whether an integrated inductor is required).
By selecting an appropriate topology, the DC-DC converter IC can significantly enhance the efficiency and adaptability of the power supply system, meeting the stringent requirements of modern electronic devices for power consumption and size.
