The Research Of High-speed Optocoupler Isolation Amplifier

Tokamak is a complicated electromagnetic device. When the operation is processing,the signal of the diagnosis, power supply, and other subsystems is very susceptible tointerference in complex environment of large current, high voltage and strong magneticfield and so on. And in the case of direct access to acquisition card or industrial PC, it iseasy to damage the electronic control system components of the industrial PC and the card.It is very necessary to isolate, process, and modulate the kinds of signals for the tokamakdevice. Based on the optocoupler with single light source and double photodiodes, thescheme of the high-speed optocoupler isolation amplifier and its technologies is studied inthis paper.The main circuit is based on the structure of the simplified compensation with singleoptocoupler, and the dc constant current source and power supply are designed at the sametime. When calculating the expression of dc signal transmission, an important conclusionis that the feedback structure eliminates the influence of the current transmission ratio ofthe optocoupler. Using linear method to calculate the transfer function in the frequencydomain, and using MATLAB to draw the bode chart, analyzing the amplitude frequencyand phase frequency characteristics. Using Pspice to simulate the circuit, to verify thecorrectness of the circuit parameters selection, to provide a basis for the circuit design andshorten the time and money. Drawing the PCB board by putting the devices reasonably torealize the power, input and output have the isolation spacing. Through the practical testand debugging repeatedly, the circuit realizes the nonlinearity of less than0.5%and2MHZ bandwidth.According to the needs of power supply system operation of J-TEXT, analog anddigital isolation cases have been developed. Analog isolation case has32channels for input and4channels for output, and the signal transmission gain is1:1, the nonlinear errorless than0.1%, delay time less than10us, the max amplitude can be up to10V, the noiseis less than20mV. Digital isolation case has16channels for input and16channels foroutput, the bandwidth is more than10KHZ, time delay less than1us, input signal rangeis5-30V, and output can drive the relay load. These boxes have been put into thelaboratory, get good performance, and meet the demand of the system operation.