@@@F_Titel linear opto-isolator @@@F_Text The fact that the Texas Instruments TIL300 opto-isolator contains two photodiodes is exploited here to endow the device with a virtually linear transfer characteristic. The trick is to include one of the photodiodes in the feedback circuit of the LED driver, while the other is used to drive an output buffer as usual. Assuming that the two photodiodes are virtually identical, the feedback circuit irons out any non-linearity of the transmit diode and the photodiode. Although the circuit shown here was not tweaked for optimum performance, non- linearity should be less than 2% or so, which is not bad for such a simple setup. The thing about using a TLC271 here is that its common-mode range goes down to 0V, allowing small input and output voltage levels to be used also, while the supply voltage may remain asymmetrical. A prototype of the circuit produced an output signal of 10Vpp at 50kHz, albeit at considerable distortion. For accurate operation, the frequency should be much reduced. In this respect, it is recommended to experiment with the value of C1, which may need to be fine-tuned to achieve the best possible frequency compensation (strive to minimize overshoot in the output signal). Also, the TLC271 is used in high-bias mode here (pin 8 tied to ground). No doubt the use of faster and more accurate opamps will produce even better results. (974022) @@@F_Klickfont @@@Klickbild 11.EPS Circuit diagram @@@F_Text
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