⒈ Composition Switch Circuit When the input signal UI is low power, the transistor V1 is in the cut-off state, the photoelectric coupler B1 the light-emitting diode current approximately is zero, the output end Q11, the Q12 resistance is very big, is equivalent to the switch "disconnect"; When the UI is high, the V1 leads, the B1 the light-emitting diode glows, Q11, The resistance between the Q12 is smaller, which is equivalent to the switch "connect". This circuit because the UI is low electricity peacetime, the switch does not pass, therefore is the high level conduction state.
Similarly, because no signal (UI is low level), switch conduction, it is low level conduction state. 2.Compose logic circuit The circuit is "with the door" logic circuit. Its logical expression is p=a. B. The two photo-sensitive tube series, only when the input logic level a=1, b=1, output p=1.
Similarly, it can be composed of "or door", "and Not Door", "or Not door" logic circuits.
3.Composition Isolation coupling circuit The circuit is shown in Figure 4. This is a typical AC-coupled amplifier circuit.
The linear amplification of the circuit can be ensured by selecting the current limiting resistor RL of the luminous circuit, so that the B4 ratio is a constant.