What are the strict requirements of high-precision equipment on the ripple and noise of LED switching power supply?
Publish Time: 2025-03-31
In the field of precision machining, the positioning accuracy of laser marking machines can reach micron level, and its core components have almost stringent requirements on the purity of the power supply system. As a key link in energy conversion, the ripple and noise level of LED switching power supply output directly affects the stability of the laser, marking accuracy and equipment life. This special requirement makes it difficult for ordinary industrial power supplies to meet the requirements, and a specially optimized power supply solution must be adopted.
Ripple factor is the core indicator for measuring the purity of power supply output. Laser marking machines usually require the ripple voltage of power supply output to be controlled within 1%, and high-end models even require less than 0.5%. Taking the 48V power supply system as an example, its peak-to-peak ripple voltage shall not exceed 240mV. This stringent standard stems from the laser modulation characteristics-the power supply ripple will be directly coupled to the laser diode drive current, resulting in beam energy fluctuations. When performing precision QR code engraving, a 0.1% current fluctuation may cause uneven marking depth. Test data of a certain brand of fiber laser marking machine shows that when the power supply ripple is reduced from 1% to 0.3%, the edge clarity can be improved by 40%. To achieve this performance, the power supply needs to adopt a multi-stage filtering design, including the combined application of π-type filtering, common mode chokes and low ESR solid capacitors.
High-frequency noise interferes with the control system more hidden. The MHz-level noise generated by the switching power supply will affect the equipment through two ways: conduction and radiation: conducted noise may interfere with the PID control loop of the laser, causing the galvanometer positioning drift; radiated noise may be received by the signal line, causing the encoder to read incorrectly. Tests in an industrial laboratory show that when the power supply EMI noise exceeds 60dBμV, the repeatability of the laser marking machine will decrease by 15%. This requires that the power supply must meet the CISPR 32 Class B standard, and at the same time adopt star grounding, guard ring and other designs on the PCB layout to control the noise below 50mVp-p. Modern high-end power supplies will integrate nanocrystalline magnetic rings and three-stage EMI filters to attenuate the noise spectrum by more than 40dB above 100MHz.
Dynamic response capability is another key consideration. The load of the laser marking machine changes dramatically during operation. In pulse mode, the current may jump from 10% to 100% in microseconds. The adjustment rate of ordinary power supplies is difficult to keep up with this change, which will cause instantaneous voltage drops. High-quality LED switching power supplies will use digital control technology to compress the transient response time to within 50μs and control the voltage fluctuation within the range of ±1%. The measured data of a certain model of CO2 laser marking machine shows that after using a power supply with feedforward compensation, the geometric distortion rate of high-frequency pulse engraving is reduced from 3% to 0.8%. This requires the feedback loop bandwidth of the power supply to reach more than 1/5 of the switching frequency, and at the same time cooperate with the adaptive gain adjustment algorithm.
Temperature stability should not be ignored either. When the laser equipment is working continuously, the internal temperature can reach more than 60℃, and the ESR of the electrolytic capacitor will increase sharply with the temperature, resulting in a decrease in filtering performance. Military-grade power supplies will use all-solid-state capacitor design to keep the ripple fluctuation within 20% of the initial value in the range of -40℃~85℃. A company conducted a comparative test and found that after 4 hours of full-load operation, the ripple of ordinary power supplies increased by 3 times, while the power supply using tantalum polymer capacitors only increased by 15%, which is crucial for assembly lines that require long-term operation.
To meet these stringent requirements, modern laser equipment power supplies are moving towards intelligence. The built-in DSP controller can monitor the output waveform in real time, identify the noise components of a specific frequency band through FFT analysis, and dynamically adjust the PWM parameters. Some models also integrate ripple compensation function, which automatically injects reverse current to offset abnormal fluctuations when abnormal fluctuations are detected. These technological innovations make the output purity of the latest generation of laser marking machine power supplies close to the level of laboratory linear power supplies, while the efficiency remains above 93%.
From the perspective of industrial practice, power supply ripple control has become an important indicator for laser equipment classification. Entry-level marking machines can accept 1%-2% ripple, industrial-level requires 0.5%-1%, and precision models used for chip marking must be controlled below 0.3%. This difference is directly reflected in the price of the equipment-for every 0.1 percentage point reduction in ripple, the power supply cost may increase by 20%. However, for application scenarios that pursue extreme precision, the yield improvement gained from this investment can often create greater value.
In the future, with the development of ultrafast laser technology, the requirements for power purity will continue to increase. Femtosecond lasers already require current control with ps-level precision, which will drive the evolution of switching power supplies to ultra-low noise architectures. The application of wide bandgap semiconductor devices such as GaN can enable the switching frequency to break through the MHz threshold, providing more design space for filtering. It can be foreseen that in the field of precision machining, power supply ripple and noise control will continue to be the core competitiveness, driving the innovation boundary of power electronics technology.
