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All colleagues unite and focus their efforts to write a new chapter of developmentSwitching Power Supply Adapter Testing: Key Points You Must Know!
所属分类： Industry News
发布时间：2020-06-23
In
Switching power adapter In the research, development, and testing phases of new product innovation, the verification stage is a critically important step that R&D personnel must pay close attention to. When testing new switch-mode power adapter products, engineers often rely on oscilloscopes to carry out debugging. So, what specific issues should we be particularly mindful of during this process? Suyuan Technology has compiled a summary of these concerns—let’s take a look.
Safety During Debugging In the debugging process of new switching power adapter products, safety concerns take top priority, with accuracy in operation and appearance coming second. During testing, special attention must be paid to the primary input circuit of the switching power supply, which can carry voltages as high as several hundred volts or even over a thousand volts. Moreover, the negative terminal of this primary circuit is not at zero voltage; therefore, if a person comes into contact with it, an electric shock may occur, posing a serious risk to the engineer’s personal safety. Additionally, connecting this terminal to ground can cause a short circuit in the power supply, damaging the rectifier components on the input side. For these reasons, when debugging a switching power supply, it is essential to first establish electrical isolation via an isolation transformer. With such isolation in place, the negative terminal of the primary circuit can be directly connected to the oscilloscope probe’s ground lead, and the oscilloscope’s three‑wire single‑phase plug can be linked to the protective earth conductor of the power system, thereby eliminating potential safety hazards. If the technician uses an oscilloscope equipped with built-in isolation capabilities during debugging, measurements can be taken directly without an isolation transformer, and no short circuit will occur. However, human contact with the primary circuit could still result in electric shock. Therefore, it remains best practice to connect an isolation transformer throughout the debugging of switching power adapters.
Key waveform in
Switching power supply During the inspection of new adapter products, engineers must pay close attention to key waveforms. When using an oscilloscope, the drain‑voltage waveform of the power switch directly reveals information such as drain‑peak voltage, secondary reflection voltage, and the on‑state voltage drop across the switch. Even with a very low input voltage, an open‑circuit condition in the drain‑snubber circuit can generate extremely high drain‑peak voltages, potentially leading to breakdown and failure of the power switch—so engineers should exercise particular caution. Furthermore, if the power switch fails to turn on fully, significant power losses may occur, causing excessive heating and eventual damage. By closely monitoring the drain‑voltage waveform, engineers can promptly detect potential hazards, shut down the power supply in time, and prevent component failure and greater losses. Probe Selection and Connection When using an oscilloscope to measure new switching‑mode power‑adapter products, engineers should choose the appropriate probe based on the specific measurement task at hand to achieve the most accurate results. For routine measurements, a 10:1 probe is usually sufficient; however, for low‑amplitude signals, a 1:1 probe is recommended. When measuring high voltages—such as the source‑terminal voltage of a switching transistor—a high‑voltage probe should be selected. Similarly, when using an oscilloscope to characterize the current waveform of adapter test samples, it is essential to select a suitable current probe.
In general, oscilloscope probes typically have an input voltage rating of 400 V (RMS) or 400 V DC, with a limited ability to tolerate short‑term peak voltages exceeding this specification. If the peak voltage is relatively high, a high‑voltage probe should be selected. When using current probes for measurements, connect them whenever possible to circuits where the voltage variations are minimal. For example, when measuring the drain current of a power switching transistor, connect the probe to the source circuit of the transistor to directly monitor the drain current. Connecting it to the drain circuit, on the other hand, can allow high‑frequency spike voltages at the drain to significantly disturb the measurement. Proper Grounding Practices When using an oscilloscope to test new switch‑mode power supply adapters, proper grounding is equally critical. During testing, if the technician grounds the probe via its ground clip, this effectively introduces a series inductance into the ground path. This series inductance, together with the probe’s capacitance, can lead to oscillations and overshoots. Switching power supplies generate strong electromagnetic emissions, and excessively long probe ground leads can also introduce noise. Furthermore, the transient currents in switch‑mode power supplies can induce disturbance voltages on the circuit board; measurements taken at different ground points may yield varying waveforms, and some waveform jitter is normal.