Domestic Optocoupler Substitute —— Advanced Optical Semiconductor
The structure of high-speed optical coupler is different from that of ordinary optical coupler.
Structurally, high-speed optical couplers are different from ordinary optical couplers. The structure of high-speed optocoupler is photodiode+amplification drive circuit, and the structure of ordinary optocoupler is phototransistor (+amplification drive circuit). The response speed (rise and fall time) of photodiode is nanosecond, and the response speed of phototransistor is microsecond. It doesn't mean that ordinary optocouplers can work at high speed in linear region, and their inherent response time is limited, so they can't think fast. In addition, if the common optocoupler works in the linear region, it will also be limited by the parameter Fc (cut-off frequency), which is about 50KHz (test conditions VCC=5v, IC=5ma, RL= 100R, and the increase of RL Fc will be smaller, and when RL= 1K, Fc will be about 10. Like TLP52 1, Fc is about 50KHz, PC8 17, Fc is about 80KHz, CNY 1 17, Fc is about 250KHz.
Of course, under the conditions of increasing the driving current (to 200MA)/ reducing the load resistance (to 500OHM)/ optimizing the driving pulse, some ordinary optocouplers can indeed reach the speed of 500KHz (some optocoupler manufacturers' application notes mentioned similar applications).
The comparison between 6N 135 and TLP52 1 is really incorrect.
If only the receiving diode of 6N 135 is used and the output of Ib series resistor (larger) is used, it will have a great impact on TpLH, which is really unfair, and no one is stupid enough to use it like this.
TLP52 1 uses phototransistors with current transmission ratio, which makes the ingenious design of external amplification and shaping circuits applied.
There is no optimized circuit for RS-485 optical isolation.
Due to time constraints, RS485 has not been optimized, nor has it been optimized into a pleasing drawing.
I dug it out from the circuit I made before, and gave it to my friends for reference.
It is not easy to ensure that the optocoupler is in a linear state. The current transmission ratio of the optocoupler changes too much, such as 52 1, and the current transmission ratio is between 0.5 and 6, which makes the output voltage change in the range of 0.5-6 times at the same intermediate frequency, which brings great difficulty to the definition of the later working point and is basically impossible.