In electronic devices, a stable power supply is crucial for ensuring reliable system operation. Switching power supplies (DC-DC) have become the mainstream power solution in consumer electronics, industrial control, communication equipment, and other fields due to their advantages of high efficiency, compact size, and wide input voltage range. Among these, the selection of peripheral components and PCB layout directly determine the output accuracy, ripple control, thermal performance, and long-term stability of DC-DC power supplies.
Basic Concepts of DC-DC Switching Power Supplies
1.What is a DC-DC Switching Power Supply?
A DC-DC switching power supply is a power electronic device that converts an input DC voltage through the "switching of transistors." Its core function is to transform an unstable input voltage (e.g., 12V) into a stable output voltage required by the load (e.g., 5V), while also providing capabilities such as voltage step-up/step-down, current regulation, and noise suppression. Compared to linear regulators (LDOs), DC-DC switching power supplies offer higher efficiency (typically 80%-95%) and are suitable for high-current (e.g., 6A) and wide input voltage scenarios.
2.Working Principle of DC-DC
Taking a classic DC-DC converter as an example, the left side includes input pins such as Enable (EN), Soft Start/Tracking (SS/TR), Default Settings (DEF), and Switching Frequency (FSW). These signals pass through the control logic module, which integrates protection and control units such as soft start, thermal shutdown, undervoltage lockout (UVLO), and Power Good (PG) control, to drive the power control module. The power control module uses a gate driver and high-side/low-side current limit comparators (HS lim, LS lim) to control the upper and lower power transistors, enabling energy conversion. The DCS-Control™ section at the bottom performs feedback regulation through an error amplifier, slope compensation, comparator, and timer. The right side includes interfaces such as power input (PVIN, AVIN), ground (AGND, PGND), and switching output (SW), collectively achieving efficient DC-DC conversion and precise control.
3.The Core of DC-DC Lies in the "Switching - Energy Storage - Filtering" Cycle:
Switching Stage:
The internal MOSFET switches (high-side HS-FET and low-side LS-FET) turn on and off alternately, "chopping" the input DC voltage into a high-frequency pulse voltage.
Energy Storage Stage:
The inductor stores energy when the switch is on, and the capacitor smoothens the pulse voltage.
Output Stage:
The feedback circuit monitors the output voltage in real time and adjusts the switch on/off time (duty cycle) to deliver a stable output voltage.
4.Key Performance Indicators
Input/Output Voltage Range: The input voltage must match the chip's tolerance range, while the output voltage must meet the load requirements (e.g., a certain DC-DC supports 5.5V-18V input and 0.611V-15V output).
Output Current: The maximum output current must cover the load's peak current (e.g., a 6A load requires a chip with ≥6A output capability).
Switching Frequency: Higher frequencies allow for smaller inductor and capacitor sizes but increase switching losses (common frequencies range from 200kHz to 1MHz, requiring a balance between efficiency and component size).
Voltage Ripple: The fluctuation value of the output voltage (industrial applications typically require ≤20mV; excessive ripple can interfere with sensitive circuits).
Efficiency: The ratio of output power to input power. Higher efficiency reduces thermal stress.
