• 1- PC817 – general characteristics of the circuit
• 2- PC817 – pinout description
• 3- PC817 – replacements and other variants
• 4- PC817 – practical applications of the optocoupler
• 5- PC817 – optocoupler parameters
• 6- PC817 – applications in electronics

Reading Time 8 min.

PC817 – general characteristics of the circuit

The PC817 is an opto-isolator, also known as an optocoupler. It is commonly used to enable signal transfer between two isolated circuits while providing electrical isolation. Here are the general characteristics of the PC817:

1. Structure: The PC817 consists of a light-emitting diode (LED) and a phototransistor, encapsulated in a single package. The LED emits light when forward biased, and the phototransistor is activated by the light emitted from the LED.
2. Isolation: It provides electrical isolation between input and output, typically rated at 5,000 volts, making it suitable for protecting sensitive components from high voltages.
3. Current Transfer Ratio (CTR): The CTR is a key parameter, representing the ratio of the output current (phototransistor) to the input current (LED). For the PC817, the typical CTR is between 50% to 600%, depending on the model and operating conditions.
4. Input/Output Voltage: The forward voltage (V_f) of the LED is typically around 1.2 to 1.4 volts. The phototransistor can handle a collector-emitter voltage (V_ce) of up to 80 volts.
5. Switching Speed: The typical rise and fall times for the output signal are relatively quick, allowing it to be effective in high-frequency applications, though it is not as fast as some advanced opto-isolators.
6. Applications: Common uses include signal isolation in microcontroller circuits, enabling communication between different voltage domains, and protecting sensitive devices in industrial and consumer applications.

When using the PC817, it’s crucial to consider the required input and output parameters for your specific application to ensure effective isolation and performance.

PC817 – pinout description

1. Pin 1 (Anode of LED): This pin connects to the positive side of the input signal. It is the anode of the internal LED.
2. Pin 2 (Cathode of LED): This pin connects to the negative side of the input signal (usually ground). It is the cathode of the internal LED.
3. Pin 3 (Collector of Phototransistor): This pin is connected to the positive voltage supply (Vcc) of the output circuit and is the collector of the phototransistor.
4. Pin 4 (Emitter of Phototransistor): This pin connects to the ground of the output circuit and is the emitter of the phototransistor.

PC817 – replacements and other variants

4N25, 6N136, MOC3021, MOC3041, as well as 6N137.

PC817 – practical applications of the optocoupler

The PC817 optocoupler is widely used in various applications due to its ability to provide electrical isolation between circuits. Here are some practical applications of the PC817:

1. Microcontroller Interfacing:
   • Used to isolate microcontroller outputs from high voltage or noisy environments, protecting sensitive microcontroller circuits while allowing communication with external devices.
2. Signal Isolation:
   • Provides isolation for control signals in automation systems, ensuring safe operation while protecting microcontrollers or low-voltage components from high voltage spikes.
3. Switching Power Supplies:
   • Utilized in feedback loops for power supply circuits to provide voltage regulation while maintaining electrical isolation between the high-voltage input and low-voltage output.
4. Sensor Applications:
   • Used to isolate sensors (e.g., temperature or current sensors) from the conditioning circuitry, allowing safe measurement of physical parameters without direct electrical connection.
5. Relay Driving:
   • Often deployed to control relays, allowing low-current control signals to switch higher-power loads while maintaining isolation.
6. Telecommunication Systems:
   • Used in signal transmission applications to prevent ground loops and ensure that different sections of a system can operate safely and independently.
7. Data Communication:
   • Employed in data communication systems, including RS-232 or RS-485 interfaces, to isolate and protect different segments of communication networks.
8. Test and Measurement Equipment:
   • Often found in test equipment for monitoring or measuring AC voltages, providing isolation between the measuring circuits and the high-voltage system under test.
9. Audio Applications:
   • Used for isolating audio signals in mixing and processing equipment, preventing noise and interference from electrical ground differences.
10. Industrial Control Systems:
    • Commonly utilized in industrial automation to interface between control systems and high-power drives or motors, ensuring safe operation under varying load conditions.

PC817 optocoupler – parameters

• Maximum collector-emitter voltage: 80V
• Maximum collector current: 50mA
• Limit frequency: 80 kHz
• Propagation time: 18us
• Maximum operating temperature: -30*C – +100*C.
• Maximum soldering temperature: 260*C
• Storage temperature: -55*C – 125*C
• Maximum power dissipated: 200mW
• Internal resistance: 100R

PC817 – applications in electronics

The PC817 optocoupler has a very wide range of applications.
Among other things, it can be used in protection such as electrical isolation between the control stage and the power stage in frequency converters.
The PC817 is a very efficient circuit when controlled from microcontrollers.
Simple transistors can be used in addition, but because of the omitted noise factor, the optocoupler can also be used as a switch in high-frequency circuits such as frequency converters and other power electronics.