Conventional application circuit of audio amplifier circuit in photocoupler

It consists of two parts: light source and light receiver. The light source and the light receiver are assembled in the same sealed housing, and are separated from each other by a transparent insulator.

The connector manufacturer Supu summarized its working principle: adding an electrical signal to the input of the optocoupler causes the light source to emit light, and the intensity of the light depends on the size of the excitation current. This light illuminates the light receiver packaged together After going on,

The photocurrent is generated due to the photoelectric effect, which is led out from the output end of the receiver, so that the conversion of electricity to light to electricity can be realized.

The use of optocouplers for audio amplifier circuits not only plays a role in signal isolation and prevents interference between stages, but also can amplify audio signals.

The photocoupler can effectively replace the audio transformer in the circuit, and overcome the shortcomings of signal loss and distortion during the primary coupling of the audio transformer, and also has the advantages of reducing electromagnetic interference.

In the figure, VT1 and VT2 form a two-stage direct coupling amplifier circuit. The sensor or signal source signal is sent to the preamplifier composed of VT1 and VT2 after C1 and R1. The preamplifier converts the weak electrical signal into a DC component signal.

The amplified and converted signal is added to the light-emitting diode VD of the photocoupler, and the intensity of the VD's light will be changed by the strength of the Vi signal. By applying a certain bias voltage to the phototransistor in the photocoupler, the optical signal transmitted from the VD can be converted into an electrical signal and amplified,

Finally, it is amplified by VT3 and output to the post-stage as a signal source. This circuit can be typically used in the signal processing of a tape recorder, and will directly replace the isolated amplifier circuit formed by the audio transformer.