1. High common mode rejection ratio (CMRR)
Inside the photoelectric coupler, the coupling capacitance between the luminous tube and optical receiver is very small (less than 2pF), so common mode input voltage through the interelectrode coupling capacitance has a small effect on the output current, and therefore the common mode rejection ratio is very high.
2. Output characteristics
The output characteristic of photoelectric coupler refers to under certain light current IF, the relationship between the photosensitive tube (with a bias voltage VCE) and the output current IC. When IF=0, light-emitting diode doesn't glow, and the photosensitive transistor collector output current is called the dark current at this time, usually it is very small. When IF>0, under certain IF action, the corresponding IC is basically unrelated to VCE. The change between IC and IF is a kind of linear relation, and the output characteristic of the photoelectric coupler measured by the semiconductor tube characteristic diagram tester is similar to that measured by the ordinary crystal triode.
3. The photoelectric coupler used as a linear optical coupler
By providing a bias current on light-emitting diodes, and then couple the signal voltage through resistance to the light emitting diode so that phototransistor received light signal which is increased and decreased on the bias current. Its output current will linear change with input signal voltage. The photoelectric coupler can also work in the switching state and transmit pulse signals. During pulse signal transmission, there is a certain delay time between the input signal and the output signal, and the input and output delay time of the photoelectric coupler with different structures is very different.