| An enterprise entrusted us to develop a kind of equipment with high performance on water resource detection.Its has some core indicators:the output is standard sine wave, and it’s continuously adjustable within the frequency rang of 40HZ to 100 KHZ.At the same time,the load impedance of the equipment is at the range of 4 Q to 1kΩ, and it’s also continuously adjustable within the specified range, Within the scope of the frequency band and load impedance, the output waveform distortion is less than 1%, the the output power of equipment is 1 kw constantly.So far,there are some research,that PWM is applied to audio output with high fidelity, have been going on but move slowly. The reason is that some technical problems of PWM have never been overcome.First,despite the so-called PWM digital control mode is gradually replacing the analog control one,which has complex hardware design,its essence is to convert the digital signals into analog signals to control. A lot of shortcomings of traditional PWM are still unsolved,and also,problems that cannot be ignored are brought in because of the downside to algorithm and the poor performance of digital chip,such as waveform distortion, low frequency, time delay and so on.Second,with the development of switching devices with new type,high power and high speed,the development of new product that the chopping frequency of its main loop is over MHz become possible.However,there are not ultra-high speed driver module products in the current market,keeping pace with the development.Third, the use of soft switch technology, makes the power switch device in chopper or inverter have less switching loss and the circuit more efficient.Meanwhile,the power switch device can be protected by instantaneous over-current relay when circuit overload or short.But,due to the electromagnetic interference,which is brought by various of distribution parameters of circuit under the condition of high frequency, the function of the circuit may not be realized,what worse, the circuit or components on it are destroyed.For example,the peak pulse voltage with high amplitude might breakdown the power switch device.On the basis of experiment,power converter method of constant energy pulse frequency modulation experiment was proved to be feasible and correct by previous senior.The paper designs the constant energy chopper type high frequency audio synthesis system, including the control,the drive and the main loop modules.In the control circuit module,the control module of chopper in main loop,including the design,debugging process and conclusion, is emphasized.It contains the principle design and parameter determination of absolute value circuit, precision voltage-frequency conversion circuit and binary frequency circuit.Its core is that voltage-frequency conversion circuit is used to achieve the output pulse train, the frequency changing along with sine law, in other word, pulse width of the output waveform changes along with sine rule (specific width has a positive correlation with the specific amplitude of sine wave). After debugging,the highest frequency is kept in 6 MHZ stably with good linearity and used in the control of primary loop successfully. The control circuit can realize the pulse frequency modulation (PFM).In the drive circuit module, when the load capacitance is 6000 pf, the top pulse frequency reaches at 10 MHZ,transmission delay time is 8～9ns,rise and fall time is 7～ 9ns, the highest voltage of output waveform is 24V.It can meet all kinds of requirements of power field effect tube under 100A with high-speed.The debugging of main circuit is primarily to explore electromagnetic compatibility problem,and further, fulfill the goals expected of the system. As for the solutions, it mainly adopts the method of active reduction and passive compensation during the whole period,from the PCB principle design to the special transformer production, to physical assembly and debugging of the primary loop.The maximum chopper frequency is to 3 MHZ stably.From the perspective purpose of the project, at present, in addition to a target related to the power, other requirements have been up to standard even exceeded.The present achievement can be used as a power amplifier into production,and he product performance is superior to the existing power amplifier product in the market (regardless of the digital mode or analog one), the result of the test verify the practical value of the power transmission mode in the electronic circuit and prove that, in the process of ultra high frequency control of chopper, analog control mode still has a realistic meaning.The successful design of the drive module dose not only contribute to the research and development of this objective, its superior performance makes it put into production separately and used to other circuit system. |
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