The power supply is far more than a simple box; it acts as the heart of an active device, providing a consistent energy source to its components. The quality of the power supply directly impacts the performance and reliability of the entire system. To ensure that power supplies meet the required standards, they undergo rigorous testing in areas such as design, manufacturing, and quality control. This involves using advanced electronic equipment to simulate various power supply characteristics (i.e., specifications) and verify their compliance before deployment.
Engineers must consider several key factors when designing or evaluating power supplies:
1. **Input Voltage Effects on Output Voltage**
- **Absolute Voltage Regulation Coefficient (A):** This measures the ratio of the change in output DC voltage (ΔU0) to the change in input grid voltage (ΔUi) under constant load. It is calculated as K = ΔU0 / ΔUi.
- **Relative Voltage Regulation Coefficient (S):** This indicates the relative change in output voltage (ΔUo/Uo) compared to the relative change in input voltage (ΔUi/Ui), given by S = (ΔUo/Uo) / (ΔUi/Ui).
- **Grid Adjustment Rate:** This reflects the relative change in output voltage when the input voltage varies by ±10% from its rated value.
2. **Load Effects on Output Voltage**
- **Load Regulation Rate (Current Regulation Rate):** Measures the maximum relative change in output voltage when the load current varies from zero to full capacity.
- **Output Resistance (Internal Resistance):** Calculated as Ro = |ΔUo / ΔIL|, where ΔUo is the change in output voltage due to a change in load current (ΔIL).
3. **Ripple Voltage Indicators**
- **Maximum Ripple Voltage:** The peak-to-peak or RMS value of ripple at rated output conditions.
- **Ripple Coefficient (Y%):** The ratio of the effective value of ripple voltage (Urms) to the DC output voltage (Uo), expressed as Y = Urms / Uo × 100%.
- **Ripple Suppression Ratio:** The ratio of input ripple voltage (Ui~) to output ripple voltage (Uo~), indicating how effectively the power supply suppresses ripple.
4. **Inrush Current**
This is the maximum instantaneous current drawn during the initial turn-on of the power supply, typically ranging from 20A to 30A.
5. **Overcurrent Protection**
Designed to protect the power supply and connected devices from damage caused by excessive current, including short circuits. The overcurrent threshold is generally set between 110% and 130% of the rated current.
6. **Overvoltage Protection**
Prevents damage from excessive output voltage, usually set at 130% to 150% of the rated output voltage.
7. **Undervoltage Protection**
Activates when the output voltage drops below a certain level, typically around 80% to 30% of the rated voltage, to prevent damage to connected equipment.
8. **Overheating Protection**
Stops the power supply and triggers an alarm if internal temperatures rise beyond safe limits.
9. **Temperature Drift and Coefficients**
- **Absolute Temperature Coefficient:** Measures the change in output voltage per degree Celsius.
- **Relative Temperature Coefficient:** Indicates the percentage change in output voltage per degree Celsius.
10. **Drift**
Slow changes in output voltage over time, even with stable input and load conditions. It can be expressed as either absolute drift (ΔUot) or relative drift (ΔUot/Uo).
11. **Response Time**
The time it takes for the output voltage to stabilize after a sudden change in load current.
12. **Distortion**
Unique to AC regulators, distortion refers to deviations from a perfect sine wave in the output waveform.
13. **Noise**
High-frequency disturbances that may affect signal integrity. For fans in power supplies, noise levels are often specified based on audible frequency ranges.
14. **Input Noise**
External noise added to the input line, measured under specific conditions to ensure proper operation.
15. **Surge Protection**
Involves applying high-voltage surges to test the power supply’s ability to withstand electrical stress without failure.
16. **Static Noise**
Repetitive pulse-like static electricity that must not disrupt normal operation.
17. **Stability**
Refers to the maximum allowable change in output voltage under operational conditions.
18. **Electrical Safety Requirements (GB 4943-90)**
Includes insulation requirements, dielectric tests, leakage current limits, and PCB material standards. Compliance with UL, CSA, VDE, and IEC regulations ensures safety and reliability.
19. **Radio Disturbance**
Measured according to standards like GB 9254-1998, covering power terminal disturbance voltage and radiated interference levels.
20. **Electromagnetic Compatibility (EMC) Tests**
Evaluate the device's immunity to electromagnetic interference and its ability to function without causing interference. Includes tests for magnetic field sensitivity, electrostatic discharge, power transients, radiation, and conducted interference.
21. **Environmental Testing**
Simulates real-world conditions such as temperature extremes, humidity, vibration, and exposure to dust or salt spray to ensure long-term reliability.
These specifications and tests are essential to ensuring that power supplies perform reliably, safely, and efficiently in a wide range of applications.
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