![]() If you add capacitor between output and GND (in fact in parallel to that 150 ohm) you get capacitive divider. ![]() In such circuit harmonic levels would be semi equal up to high frequency (the decrease in harmonic amplitude with frequency is compensated by the decreasing impedance of the capacitor). Generator connected to GND and capacitor to isolated output.įor EMC measurement that output is loaded with 150 ohm resistor to GND and disturbance at that resistor are measured. I imagine SMPS (for common mode) as AC generator in serie with its internal capacitance. SMPS circuits often have a capacitor (rated for 2kV or more) between the primary and secondary side. In high voltage generation / distribution optically triggered thyristors are sometimes used. “Medical grade” power supplies have extra demands for failing in a safe state if they fail and for lower capacitance and who knows what else.īottom line is you first have to know what to protect against before you can build something. I think it’s to ensure that the capacitance in the optocoupler is not the dominant factor in picking up noise, which could lead to faulty switching. The audio versions (S/PDIF) are the cheapest.īut for normal mains voltage related applications the ubiquitous DIP4 sized optocouplers are apparently sufficient, but would you trust a bag of cheap PC817 optocouplers from Aliexpress? ![]() If you want to go extreme you can use fiber (or plastic) optical cable. It also has other hardened features such as a 3mm internal distance between the LED and the detector, with 8kV AC and 14kV DC test voltages. ![]() Pin spacing between primary and secondary side is 15.24mm ![]()
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