PC817 Optotransistor Documentation

Introduction

The PC817 is a widely used optocoupler or optoisolator that consists of an infrared emitting diode (IRED) and a phototransistor. This electronic component is designed to transfer electrical signals through light waves, providing an optical isolation between its input and output. The PC817 is commonly used in applications requiring high-voltage insulation, signal isolation, and noise reduction, such as microcontroller interfacing, DC-DC converters, and signal transmission between different voltage circuits without direct electrical connection.

Technical Specifications

Key Technical Details

• Forward Current (IF): 50mA (max)
• Reverse Voltage (VR): 6V (max)
• Collector-Emitter Voltage (VCEO): 35V (max)
• Emitter-Collector Voltage (VECO): 6V (max)
• Collector Current (IC): 50mA (max)
• Isolation Voltage (Viso): 5000Vrms (min)
• Current Transfer Ratio (CTR): 50% to 600% at IF=5mA, VCE=5V
• Response Time (tr): 18µs (typ), 100µs (max)
• Operating Temperature: -30°C to +100°C

Pin Configuration and Descriptions

Usage Instructions

How to Use the PC817 in a Circuit

1. Connecting the Input Side (LED):

   • Connect the anode to the positive side of the input signal.
   • Connect the cathode to the negative side of the input signal through a current-limiting resistor.

2. Connecting the Output Side (Phototransistor):

   • Connect the collector to the positive side of the output circuit.
   • Connect the emitter to the negative side of the output circuit.

3. Current Limiting Resistor Calculation:

   • Calculate the current-limiting resistor for the LED side using Ohm's law: R = (Vin - Vf) / If, where Vin is the input voltage, Vf is the forward voltage of the LED (typically 1.2V), and If is the desired forward current (typically 10-20mA).

Important Considerations and Best Practices

• Ensure that the input and output circuits are properly isolated to prevent electrical noise and high-voltage transients from affecting the low-voltage side.
• Do not exceed the maximum ratings of the device to avoid damage.
• Use a pull-up resistor on the collector of the phototransistor for proper operation.
• Consider the current transfer ratio (CTR) when designing your circuit to ensure adequate signal transfer.

Troubleshooting and FAQs

Common Issues

• No Signal Transfer: Check if the input LED is properly forward-biased and the current-limiting resistor is correctly calculated.
• Weak Output Signal: Ensure that the CTR is within the required range for your application and that the phototransistor is not saturated.
• Device Damage: Verify that the device is not exposed to voltages or currents beyond its maximum ratings.

Solutions and Tips

• If the LED does not light up, check the input connections and the current-limiting resistor.
• For a weak output signal, adjust the value of the pull-up resistor or check the input current to the LED.
• Use a multimeter to check the continuity of the PC817 pins to ensure the device is not damaged.

FAQs

Q: Can the PC817 be used to isolate high-voltage circuits? A: Yes, the PC817 provides electrical isolation up to 5000Vrms, making it suitable for high-voltage applications.

Q: What is the purpose of the current-limiting resistor on the input side? A: The current-limiting resistor protects the LED from excessive current, which could lead to damage or reduced lifespan.

Q: How do I choose the pull-up resistor value for the phototransistor? A: The pull-up resistor value depends on the voltage level of the output circuit and the desired collector current. It can be calculated using Ohm's law, considering the CTR and the collector-emitter voltage.

Example Code for Arduino UNO

// Example code for interfacing PC817 with Arduino UNO

const int inputPin = 2; // Input pin connected to the phototransistor
const int ledPin = 13;  // Onboard LED pin for output indication

void setup() {
  pinMode(inputPin, INPUT); // Set the phototransistor pin as input
  pinMode(ledPin, OUTPUT);  // Set the LED pin as output
}

void loop() {
  int sensorValue = digitalRead(inputPin); // Read the value from the optotransistor
  if (sensorValue == HIGH) {
    digitalWrite(ledPin, HIGH); // Turn on the LED if the sensor is triggered
  } else {
    digitalWrite(ledPin, LOW);  // Turn off the LED otherwise
  }
}

Remember to include a current-limiting resistor for the LED side of the PC817 when connecting it to the Arduino. The example assumes that the PC817 output is connected to pin 2 and that the onboard LED is used as an output indicator. Adjust the pin numbers as necessary for your specific circuit design.