High performance ozone power supply

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High performance ozone power supply [Copy link]

Introduction
　　Surface discharge ceramic disc is a widely used ozone generating element. The driving power supply matched with it generally adopts self-excitation circuit. The ordinary self-excitation circuit has a simple structure and low cost, but has the following defects:
　　1) The operating frequency is unstable;
　　2) The output high-frequency voltage changes with the input AC voltage.
　　The ozone power supply introduced in this article adopts a separate excitation circuit, designed with EMI filter circuit and PFC circuit, with overcurrent, overheating, overvoltage protection and other functions, and also adopts voltage and current stabilization measures, and the output power is stable. It has the characteristics of high efficiency, high gas production and stable operation.

1 Load characteristics
　　Surface discharge ceramic disc is a component that uses surface discharge on the surface of ceramic dielectric to generate low-temperature plasma to achieve ozone generation function. The electrodes are arranged on both sides of the ceramic substrate. When the high-frequency sinusoidal AC voltage applied between the two electrodes is greater than the critical corona inception voltage, corona discharge is generated on the surface of the discharge electrode.
　　The ceramic disc exhibits pure capacitance properties when not discharged. The larger the surface charging area of the dielectric, the larger the equivalent capacitance. When discharging, the device exhibits dual characteristics of resistance and capacitance.
　　The ceramic disc has the following two characteristics when discharging.
　　1) When the power supply frequency is the same, the discharge energy and discharge luminous length of the ceramic disc increase with the increase of the peak-to-peak value (Vpp) of the voltage at both ends, that is, the larger the Vpp, the higher the ozone production. However, the energy density of the ceramic disc is higher when discharging, the more intense the discharge, the higher the temperature rise, and the temperature increase will in turn reduce the ozone production. In addition, too high Vpp may cause the ceramic substrate to break down and be damaged. Therefore, Vpp must be controlled within a certain range.
　　2) The critical corona inception voltage of the ceramic disc is a function of the power supply frequency. The higher the power supply frequency, the lower the critical value. Therefore, under high frequency conditions, the ceramic sheet has a lower starting operating voltage, which is conducive to the improvement of ozone production.
　　The above two characteristics of the ceramic sheet require that the power supply matching it must have a higher operating frequency and appropriate Vpp, so as to ensure that the ceramic sheet works efficiently and reliably. At the same time, in order to stabilize the ozone production, the output power of the power supply should be kept constant.

2 Working Principle and Unit Circuit
2.1 Overview of Working Principle
　　The principle block diagram of the voltage-stabilized and current-stabilized ceramic chip ozone power supply with PFC is shown in Figure 1.

　　The 220V industrial frequency mains electricity is sent to the bridge full-wave rectifier circuit after EMI filtering, and then enters the Boost circuit after rectification. Under the action of the PFC circuit, it works in the critical discontinuous conduction mode (DCM) and outputs a DC stable voltage of about 375V. At the same time, the input current follows the sinusoidal change of the input voltage, and the power factor reaches more than 0.97, which greatly reduces the pollution of harmonic current to the power grid. The PFC circuit also plays a voltage stabilizing role.
　　The 3.75V DC stable voltage output by the PFC circuit is supplied to the frequency-to-power converter circuit, and the high-frequency square wave of about 20kHz is output, which is added to the surface discharge ceramic ozone generating element through the high-voltage transformer. The load capacitor resonates with the leakage inductance of the high-voltage transformer, generating a quasi-sine wave high voltage with a peak value of about 7kV, which ionizes oxygen molecules and produces ozone.
　　In order to ensure the stability of ozone production, current and voltage feedback regulation is adopted to stabilize the output power.
　　In order to improve the reliability of power supply operation, a complete protection circuit is designed. The DC voltage overvoltage protection is completed by the PFC circuit; the sampling signals of the output voltage and current and the temperature signal inside the machine are sent to the protection circuit for comparison with the limit value. When it exceeds the limit, the protection circuit will act in time to stop the power supply from working.
2.2 EMI filter
　　The EMI filter circuit is shown in Figure 2. At the input end of the AC220V power supply, C1, C2, C3, and LT1 are connected to form an EMI filter circuit. Its function is to suppress the electromagnetic interference from the power grid, and at the same time, it attenuates the electromagnetic interference generated by the circuit itself to prevent it from interfering with other electrical equipment.

2.3 Active PFC circuit
　　The PFC circuit is shown in Figure 3, using FAN7527B as the control chip. When the input voltage is 160~260V, it can output a stable DC voltage of 375V, so that the primary voltage of the high-frequency transformer remains unchanged, eliminating the influence of grid voltage fluctuation on high-frequency output.

2.4
Main circuit and control circuit
　　The main circuit is shown in Figure 4, which uses a half-bridge circuit. The control circuit includes a drive signal generator, a PI regulator, and a protection circuit.
　　The drive signal generator uses a dedicated chip, and the values of the external R and C determine the frequency of the drive signal. Since the higher the frequency of the voltage applied to the two ends of the ceramic plate, the lower the discharge voltage, the circuit first outputs two drive signals higher than the normal working frequency for about 5s after power supply, so that the half-bridge circuit works, which is used to start the ceramic plate to prevent the ceramic plate from being damaged by sudden high voltage when it is cold.
　　The protection circuit is composed of a voltage comparator. Under normal circumstances, the temperature signal and current and voltage signals detected from the external circuit are sent to the comparison circuit on the control board. When the detection signal does not exceed the allowable range, the control circuit works normally. When the detection value exceeds the allowable range, the signal output by the comparator will stop the drive signal generator from working. When the temperature drops below the allowable value, the circuit automatically resumes working. When overcurrent and overvoltage are detected, the circuit stops working and must be powered on again to resume working.
　　The sampling signals of the output current and voltage are sent to the PI regulator to generate an error signal to control the frequency of the converter, thereby stabilizing the output power of the power supply and achieving the purpose of stabilizing the gas production. Experiments have shown that the voltage applied to both ends of the ceramic plate is slightly higher than the corona inception voltage to improve efficiency and stability. Therefore, it is necessary to stabilize the working voltage and working current.

3 Test results
　　Under the same conditions, that is, the gas source is air; the flow rate is 10L/min; the load is 2 pieces of 50mm x90mm ceramic plates in parallel; the heat dissipation method is forced air cooling, and the test is compared with the ordinary self-excited power supply. The results are as follows:
　　1) When the gas production is using this power supply, the ozone production is 1.98g after stable operation, and the gas production using the self-excited power supply is 1.08g;
　　2) When the gas production is stable, the ozone production decreases by less than 5% after continuous operation for 30 minutes when the power is turned on, while the gas production of the ordinary self-excited power supply decreases by 20%;
　　3) When the power supply is used, the power consumption is 75W, and the power consumption of the self-excited power supply is 11OW.

4 Conclusion
　　The ceramic ozone power supply introduced in this article has EMI filter circuit and PFC circuit, which can effectively suppress the interference from the power grid, meet the requirements of AC input current harmonic content limit stipulated in relevant standards, and the power factor is greater than 0.97; voltage and current stabilization measures are adopted to ensure the stability of ozone production and extend the service life of ozone generating components; the oscillation circuit works at about 20kHz, the ozone production rate is high, and the efficiency is more than 90%. Comparative tests show that under the same conditions, the ozone production of this power supply is 1.8 times that of ordinary self-excited power supply, and the power consumption is 70% of that of self-excited power supply. Using it in large and medium-sized ozone products can reduce product costs and save installation space.