How to Use Sharp PC817: Examples, Pinouts, and Specs

The Sharp PC817 is an optoisolator (also known as an optocoupler) designed to transfer electrical signals between two isolated circuits. It achieves this by using an internal light-emitting diode (LED) to transmit light to a phototransistor, which then converts the light back into an electrical signal. This design ensures electrical isolation between the input and output, making it an essential component for protecting sensitive electronics from high voltages, noise, and surges.

• Microcontroller interfacing: Isolating microcontrollers from high-voltage circuits.
• Switching power supplies: Providing feedback while maintaining isolation.
• Industrial automation: Protecting control systems from electrical noise.
• Signal isolation: Preventing ground loops in communication systems.
• Motor control circuits: Isolating control signals from high-power motor drivers.

The following are the key technical details of the Sharp PC817 optoisolator:

The Sharp PC817 comes in a 4-pin Dual Inline Package (DIP). The pinout is as follows:

1. Input Side (LED):

   • Connect the anode (Pin 1) to the positive side of the input signal through a current-limiting resistor.
   • Connect the cathode (Pin 2) to ground or the return path of the input circuit.
   • Calculate the resistor value using Ohm's Law:
     [ R = \frac{V_{in} - V_f}{I_f} ]
     Where (V_{in}) is the input voltage, (V_f) is the forward voltage of the LED (1.2 V typical), and (I_f) is the desired forward current (e.g., 10 mA).

2. Output Side (Phototransistor):

   • Connect the collector (Pin 4) to the positive supply voltage of the output circuit through a pull-up resistor.
   • Connect the emitter (Pin 3) to ground.
   • The output signal can be read across the pull-up resistor. When the LED is on, the phototransistor conducts, pulling the output low.

• Current Transfer Ratio (CTR): Ensure the CTR of the PC817 is suitable for your application. CTR varies with input current and temperature.
• Isolation Voltage: Do not exceed the rated isolation voltage of 5,000 Vrms.
• Resistor Selection: Use appropriate resistors to limit current through the LED and set the desired output voltage level.
• Temperature Range: Operate the PC817 within its specified temperature range (-30°C to +100°C) to ensure reliable performance.

The following example demonstrates how to use the PC817 to isolate a digital input signal for an Arduino UNO.

• Input Side: Connect a 5 V signal to the anode (Pin 1) through a 330 Ω resistor. Connect the cathode (Pin 2) to ground.
• Output Side: Connect the collector (Pin 4) to the Arduino's 5 V pin through a 10 kΩ pull-up resistor. Connect the emitter (Pin 3) to ground. The output signal is read at the collector.

// Define the input pin for the optocoupler
const int optoInputPin = 2; // Digital pin 2 for reading the optocoupler output

void setup() {
  pinMode(optoInputPin, INPUT); // Set the optocoupler pin as input
  Serial.begin(9600);          // Initialize serial communication
}

void loop() {
  int optoState = digitalRead(optoInputPin); // Read the optocoupler output

  // Print the state of the optocoupler
  if (optoState == HIGH) {
    Serial.println("Input signal is HIGH");
  } else {
    Serial.println("Input signal is LOW");
  }

  delay(500); // Wait for 500 ms before reading again
}

1. No Output Signal:

   • Cause: The input current to the LED is too low.
   • Solution: Check the value of the current-limiting resistor on the input side. Ensure the LED receives sufficient current (e.g., 10-20 mA).

2. Output Signal Always HIGH or LOW:

   • Cause: Incorrect pull-up resistor value or improper wiring.
   • Solution: Verify the pull-up resistor value (e.g., 10 kΩ) and ensure proper connections to the collector and emitter.

3. Signal Distortion or Noise:

   • Cause: Long wires or improper grounding.
   • Solution: Use shorter wires and ensure a solid ground connection. Add decoupling capacitors if necessary.

4. Overheating:

   • Cause: Excessive current through the LED or phototransistor.
   • Solution: Verify that the input and output currents are within the specified limits.

Q1: Can the PC817 handle AC signals?
A1: Yes, the PC817 can handle AC signals, but you must use a bridge rectifier or similar circuit to ensure proper operation of the internal LED.

Q2: What is the maximum switching speed of the PC817?
A2: The PC817 has a typical switching time of 2-4 µs, making it suitable for low- to medium-speed applications.

Q3: Can I use the PC817 for analog signal isolation?
A3: The PC817 is primarily designed for digital signals. For analog signals, consider using a linear optocoupler.

Q4: How do I choose the correct CTR range?
A4: Select a PC817 variant with a CTR range that matches your application's input and output current requirements.