The power factor correction (PFC) circuit in a ceramic ozone tube power supply significantly reduces the impact of harmonic interference on the power grid and equipment by optimizing the synchronization of the input current waveform with the voltage. Its core mechanism transforms nonlinear loads into a near-pure resistor, ensuring that the current waveform closely follows the sinusoidal voltage variation, thereby reducing the generation of higher-order harmonics. This process not only improves energy efficiency but also prevents harmonic interference with other equipment on the power grid.
Active PFC circuits are a key technology for harmonic reduction in ceramic ozone tube power supplies. Unlike passive PFC, which relies on passive components such as inductors and capacitors, active PFC utilizes power switching devices such as MOSFETs or IGBTs, combined with complex control algorithms to dynamically adjust the input current waveform. For example, the boost circuit uses high-frequency switching to boost the input voltage to a higher level while forcing the current waveform to align with the voltage waveform, achieving a power factor close to unity. This design effectively suppresses lower-order harmonics such as the third and fifth harmonics and reduces total harmonic distortion.
The PFC circuit of a ceramic ozone tube power supply typically uses either critical conduction mode (CRM) or continuous conduction mode (CCM) control strategies. CRM mode precisely controls the switching transistor by monitoring the inductor current's zero-crossing point, ensuring the current waveform remains on the boundary between continuous and discontinuous states, thereby optimizing harmonic suppression. CCM mode uses average current control technology to ensure that the average input current accurately tracks the voltage waveform, further reducing high-frequency harmonics. Both modes can be combined with a digital signal processor (DSP) or a dedicated PFC controller for high-precision regulation.
Electromagnetic interference (EMI) filters play a supporting role in PFC circuits. Connecting a common-mode choke in series with X/Y capacitors in parallel at the power supply input effectively filters out conducted interference generated by the high-frequency operation of the switching transistor. For example, the common-mode choke uses the opposing magnetic field created by its bifilar winding to offset common-mode noise, while the X capacitors suppress differential-mode interference. These filtering components work in conjunction with the PFC circuit to form a multi-stage harmonic attenuation network, ensuring that the power supply meets international harmonic standards such as IEC 61000-3-2.
The PFC design of a ceramic ozone tube power supply also needs to consider the impact of load characteristics on harmonics. As a capacitive load, the ozone tube generates pulsed current during discharge, distorting the input current waveform. The PFC circuit requires a fast-response control algorithm to compensate for this dynamic change. For example, voltage feedforward compensation can be used to predict load changes in advance, or current loop bandwidth optimization can be used to improve system dynamic performance. Some high-end designs also incorporate soft switching technology to reduce switching losses and lower high-frequency noise radiation.
Optimized heat dissipation and layout are crucial for the harmonic suppression effectiveness of the PFC circuit. Power switching devices and inductors generate significant heat at high frequencies. Poor heat dissipation can cause component parameter drift, which in turn affects harmonic control accuracy. Therefore, the design requires a low-thermal-resistance heat sink structure and a reasonable distance between the PFC module and the ozone tube. Furthermore, the PCB layout should adhere to the "short, straight, and thick" principle: shortening high-frequency current paths, reducing trace bends, and increasing copper foil thickness to reduce harmonic oscillations caused by parasitic inductance.
The PFC circuit of a ceramic ozone tube power supply must also undergo rigorous electromagnetic compatibility (EMC) testing to verify its harmonic suppression performance. Test items include conducted interference, radiated interference, and harmonic current emissions, covering the frequency range of 150kHz to 30MHz. Problems revealed during testing can be corrected by adjusting PFC controller parameters, optimizing filter component parameters, or adding shielding measures. For example, wrapping the power cable with a braided metal mesh can effectively suppress radiated interference, while increasing the capacitance of Y capacitors can improve common-mode noise filtering.
