12/7/2023 0 Comments Optoisolator circuitI’m guessing that you saw my earlier post about EasyEDA in this thread:īut if not there’s a bit more background to it there. The opto-isolator diodes should have a separate connection to the external loads positive supply. This will drop the voltage thats turning on Q8 in the first place so Q8 will start to turn off. The spice model is available for this device (but has not gone into EasyEDA yet). When the opto-isolator turns on Q8s gate will get charged turning on Q8. To try to make a 10MHz – 20MHz bandwidth galvanically isolated (AC coupled) high impedance scope probe.įor lower frequency precision isolated DC amplification? I’m looking at optoisolators and optocouplers at the moment because I’m tinkering around with a hybrid of this: That isn’t specified in the datasheets either. While it provides no isolation, the transfer function is identical. An Optoisolator or Optocoupler has different types phototransistor type, photodarlington transistor type, photo TRIAC type, and a photo SCR. Pin 3 and 5 are to be left floating in the circuit. Pin 4 and 6 contain the TRIAC with the Zero Crossing circuit. To make test and evaluation easy, I used a single dual op amp and only one 12V supply. The 1 and 2 pins consist of the anode and cathode of the infrared emitting diode. R4 is adjusted so that it drops about 2V at maximum signal level –this is very non-critical.Ĭ1 is a compensation capacitor –for faster performance, this may be adjusted down –if too low, the circuit may oscillate. Potentiometer R4 accommodates gross variations in the CTR (both devices). The easiest way to test performance is to connect a DVM between input and output. Adjusting R2 so that R1 + R2 ✴.7K causes the output of U2 to come close to the input voltage signal –further adjustment of R2 will trim for the difference in CTR so that the output voltage will exactly match the input voltage. At the same time the output of U3A presents a positive going signal to U2. When both op amp inputs are equal, the output of U1 stops integrating. U3-B turns on and provides a positive going feedback signal. At any rate, the LM358 is very inexpensive.Ī positive signal input causes the output of U1 to shift positive. There is the LM321 single op amp, but it is unpopular and comes only in the SO-23-5 SMD package. I do this because there is no DIP single device that will do the job (that I know of). I generally use the LM358 dual op amp whenever I need a single ground sensing op amp. To maintain a high voltage rating, use two single devices and match the CTR to some degree. While DIP optical couplers have up to about 5kV isolation capability, this circuit cannot support above about 100V or so because one of the outputs is fed back to the input amplifier –this puts the voltage isolation between adjacent pins on the device rather than across the device.
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