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

The Sharp PC847X is an optoisolator (also referred to as an optocoupler) designed to provide electrical isolation between its input and output. It achieves this by using an internal light-emitting diode (LED) and a phototransistor. When the LED is activated, it emits light that is detected by the phototransistor, enabling signal transmission without a direct electrical connection. This isolation is crucial for protecting sensitive components from high voltages, electrical noise, or ground loops.

• Isolation between high-voltage and low-voltage circuits
• Signal transmission in noisy environments
• Microcontroller interfacing with high-power devices
• Protection of sensitive components in industrial control systems
• Communication between systems with different ground potentials

The Sharp PC847X series includes multiple variants (e.g., PC847, PC847C, etc.), but the general specifications are as follows:

• Input Forward Voltage (VF): 1.2V (typical) at 20mA
• Input Forward Current (IF): 50mA (maximum)
• Collector-Emitter Voltage (VCEO): 35V (maximum)
• Isolation Voltage: 5000Vrms (minimum)
• CTR (Current Transfer Ratio): 50% to 600% (depending on the variant)
• Operating Temperature Range: -30°C to +100°C
• Package Type: 4-pin DIP or SMD

The Sharp PC847X has a 4-pin configuration. The pinout is as follows:

1. Input Side (LED):

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

2. Output Side (Phototransistor):

   • Connect the collector (Pin 4) to the positive voltage supply (VCC) through a pull-up resistor.
   • Connect the emitter (Pin 3) to the ground of the output circuit.
   • The phototransistor will conduct when the LED is activated, pulling the output low.

• Current Transfer Ratio (CTR): Ensure the CTR of the specific PC847X variant meets your circuit requirements. CTR determines the relationship between the input current and the output current.
• Isolation Voltage: Verify that the isolation voltage rating (5000Vrms) is sufficient for your application.
• Resistor Selection: Use appropriate resistors to limit the LED current and set the pull-up voltage for the phototransistor.
• Temperature Range: Operate the component within the specified temperature range (-30°C to +100°C) to ensure reliability.

The following example demonstrates how to use the Sharp PC847X to isolate a digital signal from an Arduino UNO.

• Input Side:
  • Connect Pin 1 (Anode) to Arduino digital pin 3 through a 220Ω resistor.
  • Connect Pin 2 (Cathode) to Arduino GND.
• Output Side:
  • Connect Pin 4 (Collector) to 5V through a 10kΩ pull-up resistor.
  • Connect Pin 3 (Emitter) to GND.

// Sharp PC847X Optoisolator Example
// This code demonstrates how to send a signal through the optoisolator
// and read the isolated output.

const int inputPin = 3;  // Arduino pin connected to the optoisolator input
const int outputPin = 2; // Arduino pin connected to the optoisolator output

void setup() {
  pinMode(inputPin, OUTPUT); // Set input pin as output
  pinMode(outputPin, INPUT); // Set output pin as input
  Serial.begin(9600);        // Initialize serial communication
}

void loop() {
  digitalWrite(inputPin, HIGH); // Turn on the LED inside the optoisolator
  delay(500);                   // Wait for 500ms
  int outputState = digitalRead(outputPin); // Read the isolated output
  Serial.print("Output State: ");
  Serial.println(outputState);  // Print the output state to the serial monitor

  digitalWrite(inputPin, LOW);  // Turn off the LED
  delay(500);                   // Wait for 500ms
}

1. No Output Signal:

   • Cause: Insufficient input current to the LED.
   • Solution: Check the input resistor value and ensure the forward current (IF) is within the recommended range.

2. Output Signal is Always High:

   • Cause: Incorrect pull-up resistor value or damaged phototransistor.
   • Solution: Verify the pull-up resistor value (e.g., 10kΩ) and check the phototransistor connections.

3. Output Signal is Always Low:

   • Cause: LED not turning off or short circuit on the output side.
   • Solution: Ensure the input signal properly toggles the LED and check for shorts.

4. Excessive Heat:

   • Cause: Overcurrent through the LED or phototransistor.
   • Solution: Use appropriate current-limiting resistors and ensure the component operates within its rated limits.

Q1: Can the PC847X handle AC signals?
A1: Yes, the PC847X can handle AC signals on the input side, but you must use a rectifier circuit to ensure proper operation.

Q2: What is the difference between PC847 and PC847C?
A2: The difference lies in the Current Transfer Ratio (CTR) range. Check the datasheet for specific CTR values for each variant.

Q3: Can I use the PC847X for high-speed signal transmission?
A3: The PC847X is suitable for low to moderate-speed signals. For high-speed applications, consider optoisolators designed for faster switching.

Q4: How do I calculate the input resistor value?
A4: Use the formula:
[ R = \frac{V_{in} - V_F}{I_F} ]
where ( V_{in} ) is the input voltage, ( V_F ) is the forward voltage (1.2V), and ( I_F ) is the desired forward current (e.g., 10mA).