Service & Support

A: A switching power supply is a device that converts input electrical energy by rapidly turning a high-frequency switching transistor on and off, effectively "chopping" the input power. This chopped power is then processed through a transformer, rectified, and filtered to output a stable DC voltage. Its core principle is "switching" regulation.

Key Differences:

Efficiency: Switching power supplies are highly efficient (typically >80%), while linear power supplies have lower efficiency (typically 40-60%).

Size & Weight: Switching power supplies are compact and lightweight (due to smaller high-frequency transformers), whereas linear power supplies are larger and heavier (using bulky line-frequency transformers).

Noise: Switching power supplies generate high-frequency switching noise; linear power supplies have very low noise.

Ripple: Switching power supplies have larger output ripple; linear power supplies provide very clean output.

Application: Switching power supplies are used in the vast majority of electronic devices. Linear power supplies are used in applications extremely sensitive to noise, such as analog/audio circuits and laboratory equipment.

A: A switching power supply first rectifies the input AC power into high-voltage DC power. This high-voltage DC is then converted into high-frequency AC through a high-frequency oscillation circuit composed of switching components (such as MOSFETs). Next, this high-frequency AC is stepped down or up via a high-frequency transformer. Finally, it undergoes rectification and filtering again to output a stable, clean DC voltage. The core principle relies on "high-frequency switching" to achieve highly efficient power conversion.

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Key parameters to consider include:

Output Voltage (V): Must match the voltage required by the device.

Output Current (A) or Power (W): The power supply's rated output current/power must exceed the device's maximum demand. A 20-30% margin is recommended to ensure long-term stable operation.

Input Voltage Range: Ensure compatibility with your local power grid (e.g., a universal input of 85-264V AC suits most regions globally).

Dimensions & Mounting: Check that the physical size and mounting holes fit your device's requirements.

Safety Certifications: Choose products with certifications relevant to the sales region (e.g., UL, CE, CCC, TÜV).

Environmental Requirements: For outdoor, high-temperature, or humid environments, select industrial-grade models or those with higher protection ratings (e.g., IP rating).

Special Features: Determine if functions like PFC (Power Factor Correction), remote control, redundancy, etc., are needed.

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Efficiency = (Output Power / Input Power) × 100%. It is an indicator that measures the power supply's ability to convert input electrical energy into useful output electrical energy.

Importance:

Energy Saving & Heat Generation: Lower efficiency means more energy is lost and dissipated as heat. This not only wastes electrical energy but also leads to higher internal temperatures in the power supply, affecting component lifespan and reliability. It may also necessitate larger heat sinks or fans, increasing cost and size.

Thermal Management: High efficiency means less heat generation, enabling more compact and reliable system design.

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This is primarily because the switching transistor operates in only two states: "fully ON" and "fully OFF." Ideally, the power loss in both these states is very low. The main losses occur during the brief transition between states, known as "switching loss," and during the ON state, called "conduction loss." Through optimized design and the use of fast-switching devices, these losses can be minimized.

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Ripple: Caused by the high-frequency switching operation of the switching device, it is a high-frequency periodic component superimposed on the DC output.

Noise: Spike interference generated by the rapid switching (ON/OFF) of the switching device.

Methods to Reduce:

Connect high-quality, low-ESR (Equivalent Series Resistance) ceramic capacitors and electrolytic capacitors in parallel at the power supply output.

Add an LC (Inductor-Capacitor) filter circuit.

In layout design, shorten high-frequency loop paths and use ground planes for shielding.

For sensitive equipment, additional external components like ferrite beads or π-type filters can be used.

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Definition: Refers to the power consumed by the switching power supply itself when it is connected to the input voltage but not supplying any load (no-load condition).

Importance:

Energy Saving & Environmental Protection: For devices that are always plugged in (e.g., phone chargers, TVs, computers), the power supply consumes energy even when the device is off. Low standby power consumption complies with global green energy standards.

Operating Costs: Power supplies with high standby consumption can silently increase electricity bills.

Quality Indicator: Typically, power supplies utilizing advanced technology and chips can achieve very low standby power consumption (e.g., less than 0.1W).

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Definition: Refers to the duration for which the output voltage of a switching power supply can remain within specification after the AC input power is interrupted (typically required to be at least 16ms-20ms, equivalent to one cycle of a 50Hz power grid).

Importance:

For equipment such as servers and industrial controllers, the hold-up time ensures that during a momentary power interruption (e.g., during grid switching), the device has sufficient time to complete critical data saving and shut down properly, or to switch to a backup power source (such as a UPS).

This parameter is primarily determined by the capacitance of the electrolytic capacitors on the high-voltage DC bus. A larger capacitor capacity stores more energy, resulting in a longer hold-up time.

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Protection features are crucial for ensuring the safety of both the power supply and the connected equipment. Common protection functions include:

Over-Current Protection (OCP): Limits or shuts off the output when the current exceeds the set value.

Over-Voltage Protection (OVP): Shuts down the output when the voltage abnormally increases to prevent damage to downstream devices.

Short-Circuit Protection (SCP): Immediately shuts off or limits the output current when a short circuit is detected at the output terminals.

Over-Temperature Protection (OTP): Automatically deactivates the output when the internal temperature exceeds the safe limit. It may automatically restore or require a manual restart after the temperature normalizes.

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PFC is a technology used to improve the power supply's "power factor". The power factor is the ratio of real power to apparent power, reflecting the utilization efficiency of effective power from the grid.

Why it's needed:
Switching power supplies without PFC draw input current in sharp pulses rather than a sinusoidal waveform, resulting in a very low power factor (possibly only 0.4-0.6). This increases the burden on the power grid, causes energy waste, and can interfere with other equipment on the same grid. Regulations in many countries and regions (such as the EU's EN61000-3-2) require equipment above a certain power level to be equipped with a PFC circuit.

Function: The PFC circuit shapes the input current waveform to follow the input voltage waveform, increasing the power factor to 0.95 or higher, thereby enabling more efficient use of electrical energy.

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Definition: Refers to the automatic balancing of output current among multiple parallel-connected switching power supplies of the same model, controlled through internal or external circuits.

Purpose: To achieve power capacity expansion (N+1 redundancy) and distribute heat loss evenly, thereby improving system reliability. Directly paralleling power supplies without current sharing functionality can lead to unbalanced output current, potentially causing one unit to overload and fail prematurely.

Additional Notes:

"N+1 Redundancy" is a common reliability design scheme in power electronics systems. "N" represents the number of power modules required for normal system operation, while "+1" indicates an additional backup module. This ensures the system remains operational even if one module fails.

"Distributing heat loss" prevents individual power modules from experiencing accelerated component aging due to overheating, thereby extending the service life of the entire power system.

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Remote ON/OFF Control:

Typically implemented through a "REMOTE" or "CTRL" terminal.

Shorting this terminal to the "COM" terminal turns the power supply ON; opening the connection turns it OFF.

Used for remotely controlling the power supply without disconnecting the input power.

Output Voltage Adjustment:

Usually features a trimmer potentiometer (labeled "ADJ" or "VR") on the power supply board.

Rotating it with a small screwdriver allows fine-tuning of the output voltage within a small range (e.g., ±10%).

Note: Do not adjust unnecessarily.

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Switching power supplies typically feature over-current protection.

Capacitive loads: When charging a large capacitor bank, the instantaneous current can be very high, potentially triggering the power supply's over-current protection or damaging it. Good power supply designs incorporate soft-start circuits to limit the inrush current.

Motor/filament loads: The resistance of motors during startup and bulbs when cold is very low, resulting in starting currents that can be several times to ten times the rated current.

Countermeasures: When selecting a power supply, ensure it can withstand the load's inrush current, or design additional soft-start circuits (such as NTC thermistors) for the load.

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This is a critical safety step when repairing switching power supplies.

Recommended Method: Use a sufficiently powerful resistor (e.g., a 10kΩ / 5W cement resistor) to briefly short the capacitor terminals for several seconds. Use a multimeter set to the voltage range to confirm the voltage has dropped to a safe level (e.g., below 36V).

Not Recommended: Never directly short the capacitor terminals with metal tools like a screwdriver. This creates intense sparking and high current, which can damage the capacitor, PCB traces, and pose a risk to the personnel.

Important Note: Some power supplies are designed with bleeder resistors that allow the voltage to decay slowly after power-off. However, never rely solely on this. Always manually verify and discharge the capacitor before any repair work.