How to Use Sharp PC847X: Examples, Pinouts, and Specs

The Sharp PC847X is an optoisolator designed to provide electrical isolation between its input and output. It achieves this by using an LED and a phototransistor, which are optically coupled but electrically isolated. This component is widely used in circuits where signal transmission needs to occur without direct electrical connection, ensuring safety and protecting sensitive components from voltage spikes or noise.

• Microcontroller interfacing with high-voltage circuits
• Signal isolation in industrial control systems
• Noise suppression in communication systems
• Power supply feedback circuits
• Motor control and inverter circuits

The following table outlines the key technical specifications of the Sharp PC847X optoisolator:

The Sharp PC847X is typically housed in a 4-pin DIP (Dual Inline Package). The pin configuration is as follows:

1. Input Side (LED):

   • Connect the anode (Pin 1) to a current-limiting resistor and then to the input signal source.
   • Connect the cathode (Pin 2) to the ground of the input circuit.
   • Ensure the forward current (IF) does not exceed the maximum rating of 50mA.

2. Output Side (Phototransistor):

   • Connect the collector (Pin 4) to the positive supply voltage through a pull-up resistor.
   • Connect the emitter (Pin 3) to the ground of the output circuit.
   • The output signal can be read across the pull-up resistor.

3. Isolation:

   • Ensure that the input and output circuits share no direct electrical connection to maintain isolation.

• Use a resistor in series with the LED to limit the current and prevent damage.
• Select a pull-up resistor value that matches the desired output signal characteristics.
• Avoid exceeding the maximum voltage and current ratings to ensure reliable operation.
• For high-speed applications, consider the rise and fall times of the optoisolator.

The following example demonstrates how to use the PC847X to isolate a digital input signal for an Arduino UNO:

• Input Side: Connect a 5V signal to the anode (Pin 1) through a 220Ω resistor. Connect the cathode (Pin 2) to ground.
• Output Side: Connect the collector (Pin 4) to the Arduino's 5V pin through a 10kΩ pull-up resistor. Connect the emitter (Pin 3) to the Arduino's ground. The output signal is read at the collector.

// Define the input pin for the optoisolator output
const int optoInputPin = 2; // Digital pin 2 on Arduino

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

void loop() {
  int signalState = digitalRead(optoInputPin); // Read the optoisolator output
  
  // Print the signal state to the Serial Monitor
  if (signalState == HIGH) {
    Serial.println("Signal HIGH"); // Output is HIGH
  } else {
    Serial.println("Signal LOW"); // Output is LOW
  }
  
  delay(500); // Wait for 500ms before reading again
}

1. No Output Signal:

   • Cause: The input LED is not receiving sufficient current.
   • Solution: Check the input resistor value and ensure the forward current is within the recommended range.

2. Output Signal is Always HIGH or LOW:

   • Cause: Incorrect pull-up resistor value or improper wiring.
   • Solution: Verify the pull-up resistor value and ensure proper connections.

3. Slow Response Time:

   • Cause: Excessive capacitance or incorrect pull-up resistor value.
   • Solution: Use a lower pull-up resistor value to improve response time.

4. Isolation Failure:

   • Cause: Input and output grounds are connected.
   • Solution: Ensure complete electrical isolation between input and output circuits.

Q: Can the PC847X handle AC signals?
A: Yes, the PC847X can handle AC signals on the input side, but you must use a rectifier circuit to ensure proper operation.

Q: What is the typical lifespan of the PC847X?
A: The PC847X has a long operational lifespan when used within its specified ratings, typically exceeding 100,000 hours.

Q: Can I use the PC847X for high-speed data transmission?
A: Yes, the PC847X is suitable for high-speed switching applications, with typical rise and fall times of 4µs and 3µs, respectively.

Q: How do I calculate the input resistor value?
A: Use Ohm's Law: ( R = \frac{V_{in} - V_F}{I_F} ), where ( V_{in} ) is the input voltage, ( V_F ) is the forward voltage (1.2V typical), and ( I_F ) is the desired forward current.

By following this documentation, you can effectively integrate the Sharp PC847X optoisolator into your electronic projects.