Linear ac analog coupler
#analog
#coupler
#phototransistor
#photodiode
#emitter follower
#ac voltage
#IRED
#linear region
#low impedance
Description: The coupler is biased in the linear region using a 10 mA DC bias on the infrared emitting diode (IRED) and a voltage divider connected to the base of the phototransistor. This configuration allows the photodiode current to flow from the base into the voltage divider, generating an AC voltage that is proportional to the AC current from the IRED. The transistor operates as an emitter follower, requiring less than 10% of the photodiode current to achieve a low impedance AC output across the emitter resistor.
Additionally, the HI 1 AVI can be used as a substitute for the 4N35, offering isolation rated for VDE line voltage of less than 0.5 pF.
The described circuit utilizes a coupler to facilitate signal transmission while maintaining isolation between the input and output. The biasing arrangement ensures that the IRED operates within its linear region, which is critical for accurate signal modulation. The 10 mA DC bias establishes a consistent operating point, allowing the phototransistor to respond effectively to variations in the AC current from the IRED.
The voltage divider configuration at the phototransistor base is essential for determining the gain and response of the circuit. By allowing photodiode current to flow into the voltage divider, the circuit produces an AC voltage that reflects the modulation of the input signal. This AC voltage is crucial for applications requiring precise signal transfer without direct electrical connection.
The emitter follower configuration of the transistor is advantageous as it provides a low output impedance, which is beneficial for driving subsequent stages in a circuit. The requirement of less than 10% of the photodiode current for operation indicates efficient use of the available current, minimizing power consumption while still ensuring adequate signal strength.
The option to substitute the HI 1 AVI for the 4N35 enhances design flexibility, allowing engineers to select components that meet specific isolation requirements. The isolation rating of less than 0.5 pF is significant in high-frequency applications, where minimizing parasitic capacitance is essential for maintaining signal integrity. Overall, this circuit design exemplifies effective signal coupling and isolation techniques in electronic systems.With the coupler biased in the linear region by the 10 mA dc bias on the IRED and the voltage divider on the phototransistor base, photodiode current flows out of the base into the voltage divider, producing an ac voltage proportional to the ac current in the IRED. The transistor is biased as an emitter follower and requires less than 10% of the photodiode current to produce the low impedance ac output across the emitter resistor.
Note that the HI 1 AVI may be substituted for the 4N35 to provide VDE line voltage rated isolation of less than 0.5 pF.
Additionally, the HI 1 AVI can be used as a substitute for the 4N35, offering isolation rated for VDE line voltage of less than 0.5 pF.
The described circuit utilizes a coupler to facilitate signal transmission while maintaining isolation between the input and output. The biasing arrangement ensures that the IRED operates within its linear region, which is critical for accurate signal modulation. The 10 mA DC bias establishes a consistent operating point, allowing the phototransistor to respond effectively to variations in the AC current from the IRED.
The voltage divider configuration at the phototransistor base is essential for determining the gain and response of the circuit. By allowing photodiode current to flow into the voltage divider, the circuit produces an AC voltage that reflects the modulation of the input signal. This AC voltage is crucial for applications requiring precise signal transfer without direct electrical connection.
The emitter follower configuration of the transistor is advantageous as it provides a low output impedance, which is beneficial for driving subsequent stages in a circuit. The requirement of less than 10% of the photodiode current for operation indicates efficient use of the available current, minimizing power consumption while still ensuring adequate signal strength.
The option to substitute the HI 1 AVI for the 4N35 enhances design flexibility, allowing engineers to select components that meet specific isolation requirements. The isolation rating of less than 0.5 pF is significant in high-frequency applications, where minimizing parasitic capacitance is essential for maintaining signal integrity. Overall, this circuit design exemplifies effective signal coupling and isolation techniques in electronic systems.With the coupler biased in the linear region by the 10 mA dc bias on the IRED and the voltage divider on the phototransistor base, photodiode current flows out of the base into the voltage divider, producing an ac voltage proportional to the ac current in the IRED. The transistor is biased as an emitter follower and requires less than 10% of the photodiode current to produce the low impedance ac output across the emitter resistor.
Note that the HI 1 AVI may be substituted for the 4N35 to provide VDE line voltage rated isolation of less than 0.5 pF.
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