Ripple suppression method for high-precision low ripple power supply

1. Hazards of Ripple and Requirements for Suppression
High-precision low-ripple power supplies are widely used in fields such as sensor power supply, precision instruments, and quantum computing. The output ripple directly affects the working accuracy of terminal equipment - for example, if a sensor power supply has a 10mVpp ripple, it will increase the sensor output error by 5%; the superconducting quantum bits in quantum computing require a power supply ripple of <1mVpp, otherwise it will interfere with the stability of the quantum state. Ripples mainly come from input noise (such as power grid harmonics), switching noise (generated by the switching of power devices), and load noise (fluctuations in load current). Therefore, it is necessary to build a ripple suppression system from three links: noise source, propagation path, and load end.
2. Ripple Suppression Methods at the Hardware Level
(1) Multi-Level Filtering: Reducing Noise from the Source
A three-level filtering structure of "input filtering + intermediate filtering + output filtering" is adopted: in the input filtering link, aiming at the 50/60Hz harmonics of the power grid, LC filtering with a power frequency inductor (inductance 10mH) + electrolytic capacitor (capacity 1000μF) is used to suppress low-frequency noise; in the intermediate filtering link, between the power conversion module and the output end, a π-type filter (inductor 50μH, capacitor 10μF) is used, and a film capacitor (capacity 1μF) is added to suppress high-frequency switching noise (100kHz-1MHz); in the output filtering link, a combination of a ceramic capacitor (capacity 100nF) with low equivalent series resistance (ESR <10mΩ) + a high-frequency inductor (inductance 1μH) is selected to further filter out the remaining high-frequency ripples (1-10MHz). Three-level filtering can reduce the ripple from 200mVpp to below 10mVpp, laying a foundation for subsequent suppression.
(2) Combination of Synchronous Rectification and Linear Regulator: Reducing Switching Noise
Aiming at the conduction loss and noise generated by traditional diode rectification, synchronous rectification technology is adopted - MOSFETs are used to replace rectifier diodes, and the DSP controls the turn-on and turn-off of MOSFETs, increasing the rectification efficiency to over 98% and reducing the switching noise generated by diode reverse recovery (noise amplitude reduced by 60%); in the post-stage of synchronous rectification, a low-dropout linear regulator (LDO) is connected in series. The LDO is a model with high power supply rejection ratio (PSRR >80dB@1kHz), which can further suppress the residual ripple in the previous stage. For example, in a 12V output power supply, synchronous rectification reduces the ripple from 50mVpp to 15mVpp, and after further processing by the LDO, the ripple can be reduced to below 2mVpp, meeting the needs of precision instruments.
(3) Electromagnetic Shielding and Grounding Optimization: Blocking Noise Propagation
A noise isolation system of "shielding layer + grounding network" is constructed: the power supply shell adopts a double-layer shielding structure (inner copper foil, outer aluminum alloy). The copper foil is used to absorb high-frequency electromagnetic radiation (above 10MHz), and the aluminum alloy is used to shield low-frequency interference; in the internal circuit, the power loop and control loop are shielded separately to avoid the switching noise of the power loop coupling to the control loop; in terms of grounding, single-point grounding (ground resistance <0.5Ω) is adopted. The power ground, signal ground, and shield ground are respectively connected to the ground bar, and then summarized to the main ground terminal to avoid noise crosstalk between different grounds. Through this design, the impact of external electromagnetic interference on the power output ripple can be reduced by 70%, ensuring that the power supply can still output stably in a complex electromagnetic environment.
3. Ripple Suppression Methods at the Software Level
(1) Optimization of Digital Control Algorithm: Real-Time Ripple Compensation
A composite control algorithm of "PID control + feedforward control + adaptive filtering" is adopted: PID control adjusts the PWM duty cycle by collecting the output ripple in real time to achieve basic ripple compensation; the feedforward control link calculates the required control quantity in advance by monitoring the changes of input voltage and load current to avoid ripple increase caused by input or load fluctuations (compensation response time <100μs); the adaptive filtering algorithm is based on the least mean square error (LMS) principle, and specifically suppresses ripples of specific frequencies (such as 50Hz power frequency and switching frequency harmonics) by analyzing the spectral characteristics of ripples. In a sensor power supply, this algorithm reduces the ripple from 5mVpp to 1mVpp, and the compensation accuracy is increased by 80%.
(2) Frequency Synchronization and Dithering Control: Reducing Beat Frequency Noise
When the power supply switching frequency is close to the external interference frequency, beat frequency noise (increased ripple amplitude) will be generated. Therefore, it is necessary to synchronize the switching frequency with the external - the frequency synchronization module receives an external synchronization signal (such as a 10MHz clock) and adjusts the power supply switching frequency to stagger it from the external interference frequency (frequency difference >10%) to avoid beat frequency generation; at the same time, frequency dithering technology is introduced to make the switching frequency change slowly within the range of ±5%, dispersing the concentrated switching noise energy into a wider frequency bandwidth and reducing the peak noise amplitude (noise peak reduced by 40%). In quantum computing equipment, this technology stably controls the power supply ripple below 0.8mVpp, meeting the power supply needs of quantum bits.
4. Comprehensive Suppression Effect and Application Verification
In a precision sensor production line, after adopting the "hardware + software" comprehensive ripple suppression scheme, the power supply output ripple is reduced from 15mVpp to 0.5mVpp, and the sensor output error is reduced from 5% to 0.8%; in the quantum computing experimental platform, this scheme makes the power supply ripple <0.3mVpp, extends the coherence time of quantum bits by 20%, and significantly improves the stability of experimental data. This method has been adapted to power supplies with various output specifications such as 5V, 12V, and 24V, and can be widely applied to various scenarios sensitive to ripples.
5. Development Direction of Ripple Suppression Technology
In the future, we will combine artificial intelligence technology to train a ripple prediction model through deep learning, realizing intelligent ripple control of "advance prediction - active suppression"; at the same time, we will develop micro-filter components based on MEMS technology to further reduce the volume of the filter module and promote the development of high-precision low-ripple power supplies towards miniaturization and intelligence.