How to Use SFH615A: Examples, Pinouts, and Specs

The SFH615A, manufactured by Valsay, is an optocoupler designed to provide electrical isolation between its input and output. It consists of an internal light-emitting diode (LED) and a phototransistor, enabling signal transmission without direct electrical connection. This isolation is crucial in protecting sensitive circuits from high voltages, noise, or ground loops.

• Signal isolation in power supplies
• Data communication systems
• Microcontroller interfacing with high-voltage circuits
• Motor control circuits
• Industrial automation systems

The SFH615A is available in various current transfer ratio (CTR) grades, making it suitable for a wide range of applications. Below are its key technical details:

The SFH615A is a 4-pin device with the following pinout:

The SFH615A is straightforward to use in circuits requiring electrical isolation. Below are the steps and considerations for proper usage:

1. Connect the LED Side (Input):

   • Connect the anode (Pin 1) to the positive side of the input signal through a current-limiting resistor.
   • Connect the cathode (Pin 2) to the ground of the input circuit.
   • Calculate the resistor value to limit the forward current (IF) to a safe level (e.g., 10 mA): [ R = \frac{V_{IN} - V_F}{I_F} ] where ( V_{IN} ) is the input voltage, ( V_F ) is the forward voltage (1.25 V typical), and ( I_F ) is the desired forward current.

2. Connect the Phototransistor Side (Output):

   • 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 the ground of the output circuit.
   • The value of the pull-up resistor depends on the desired output current and voltage levels.

3. Ensure Proper Isolation:

   • Maintain physical separation between the input and output sides to preserve isolation.

• Current Transfer Ratio (CTR): Choose the appropriate SFH615A grade based on the required CTR for your application.
• Input Resistor Selection: Always use a resistor to limit the LED current and prevent damage.
• Temperature Effects: Be aware that CTR and other parameters may vary with temperature.
• Isolation Voltage: Do not exceed the rated isolation voltage of 5300 VRMS.
• PCB Layout: Ensure proper creepage and clearance distances on the PCB to maintain isolation.

The SFH615A can be used to interface an Arduino UNO with a high-voltage circuit. Below is an example circuit and code:

• The input side of the SFH615A is connected to a digital output pin of the Arduino through a 220 Ω resistor.
• The output side is connected to a 5 V supply with a 10 kΩ pull-up resistor.

// Example code to control SFH615A with Arduino UNO
const int optoInputPin = 3; // Pin connected to SFH615A anode via resistor

void setup() {
  pinMode(optoInputPin, OUTPUT); // Set the pin as an output
}

void loop() {
  digitalWrite(optoInputPin, HIGH); // Turn on the LED inside SFH615A
  delay(1000);                      // Wait for 1 second
  digitalWrite(optoInputPin, LOW);  // Turn off the LED
  delay(1000);                      // Wait for 1 second
}

1. Can the SFH615A handle AC signals?

   • Yes, the SFH615A can transmit AC signals, but ensure the input LED is driven with an appropriate AC signal and current-limiting resistor.

2. What is the maximum switching speed of the SFH615A?

   • The SFH615A has a typical switching time of a few microseconds, making it suitable for low- to medium-speed applications.

3. Can I use the SFH615A for analog signal transmission?

   • While the SFH615A is primarily designed for digital signals, it can transmit analog signals within its linear operating range. However, the accuracy may be limited by the CTR and nonlinearity.

By following the guidelines and best practices outlined in this documentation, you can effectively use the SFH615A optocoupler in your electronic designs.