4N35 Optocoupler: Pinout, Package, Application, and 4N25 vs 4N35
29 February 2024
Ⅳ. How to use 4N35 optocoupler?
Ⅵ. How to test the 4N35 optocoupler?
Ⅷ. What is the difference between 4N25 and 4N35?
The function of an optocoupler is to disconnect the connection between the signal source and the signal receiver to prevent electrical interference. In other words, it is used to prevent interference from external electrical signals. 4N35 is an optocoupler manufactured by Lite-On and used in controllers, communication links, computer peripherals and other applications. In this article, we will provide you with information about the 4N35 with a pin diagram.
4N35 is a commonly used optocoupler device that isolates input and output circuits to provide electrical isolation and signal transmission between different circuits. Available in 6-pin DIP and SMD package options, the 4N35 consists of two parts: a light emitting diode (LED) and a photosensitive transistor. The principle of operation is relatively simple. When the light emitting diode is energized and emits infrared light, the photosensitive triode detects this infrared light, which causes the transistor to saturate or conduct. The internal photosensitive transistor has two bases that can be controlled, one for photodetection or infrared light detection, and the other is connected to pin 6 of the device, so it can be controlled by two different programs. The photocoupler is widely used for AC power detection, reed relay driving, switched mode power feedback, telephone ringing detection, logic ground isolation and logic coupling with high frequency noise rejection.
Replacements and equivalents:
• LOC110
• PC816
• 4N36
• 4N25
• 6N1136
The pin diagram of the 4N35 optocoupler is as follows:
Pin 1 (Anode): IR LED anode/positive pin
Pin 2 (Cathode): IR LED cathode/negative pin
Pin 3 (NC): Not connected pin
Pin 4 (Base): Base pin of the photo transistor
Pin 5 (Collector): Collector pin of the photo transistor
Pin 6 (Emitter): Emitter pin of the photo transistor
• Manufacturer: Lite-On
• Package / Case: PDIP-6
• Packaging: Tube
• Rise/Fall Time: 10 us
• Isolation Voltage: 3550 Vrms
• If - Forward Current: 60 mA
• VR - Reverse Voltage: 6 V
• Vf - Forward Voltage: 1.5 V
• Power Dissipation: 350 mW
• Mounting Style: Through Hole
• Number of Channels: 1 Channel
• Operating Temperature: -55°C ~ 100°C
• Product Category: Transistor Output Optocouplers
Utilizing the 4N35 Optocoupler is straightforward; it comprises an infrared light-emitting diode (IRLED) and a phototransistor, each fulfilling distinct functions. The anode pin of the LED can be connected to the output of the device that is being operated or worked on (e.g., any integrated circuit or microcontroller), while the cathode pin of the LED should be connected to the ground terminal of the device. We must apply a current limiting resistor to this LED, just like we would with any other LED.
When the output signal of the device is high, the LED is activated and emits infrared light. This light is then captured by the phototransistor, causing it to saturate or light up. As a result, a short circuit is formed between the collector and emitter pins, allowing the wires connected to these two pins (typically pins 4 and 5) to achieve interconnectivity. It's important to note that the internal phototransistor operates much like a standard bipolar junction transistor (BJT) and is controllable. Moreover, connecting pin 6 to the transistor's base enables precise manipulation of its state.
Motor circuits must protect the microcontroller (MCU) from voltage spikes from PWM-driven DC motors. For this purpose, the 4N35 optocoupler can completely isolate the MCU from the motor. At the same time, the 1N4001 buffer diode provides a ground path for reverse polarity spikes from the motor. Furthermore, incorporating a capacitor alongside the 1N4001 in parallel establishes a grounding route for elevated frequency interference. This setup is crucial in maintaining the stability and safety of the MCU during motor operation.
The parameter values of certain components in this circuit need to be determined through iterative testing to achieve optimum performance. The value of the resistor connected to the base of the 4N35 should be set for optimal fall time, typically this value may be around 1 MΩ. The capacitor connected in parallel with the motor should be a ceramic type (as electrolytic capacitors are slower to respond) and the starting value can be adjusted from ~0.1 μF. If excessive spike noise is found on the analog input, we can increase the value of this capacitor appropriately to reduce the noise interference.
The limiting factor for the PWM frequency is mainly the bandwidth of the 4N35 optocoupler. Since the device has a relatively low bandwidth, we will choose to use a PWM frequency of approximately 1kHz to accommodate its limitations.
The following are the detailed steps of the 4N35 test method:
Step one: Prepare test equipment
Proper test instruments and tools are very important for testing 4N35. First, we need a digital multimeter and a digital power supply to test the circuit connections between the pins and the output signals. In addition, we need a small LED light to test the strength of the output signal.
Step two: Test the input circuit
The test of the input terminal includes two key steps: first, testing the threshold current of the emitter tube, and second, measuring the applied voltage of the light-emitting diode.
• Test the threshold current of the transmitter: We set the digital power supply to gradually increase the current and test the threshold current of the 4N35 transmitter with a multimeter. When the current displayed by the test instrument reaches the threshold current, the LED light should start to glow.
• Measure the application voltage of the LED: We use a digital multimeter to test the reverse voltage and forward voltage of the LED in the chip to ensure that it meets the design requirements. The forward voltage should be minimal and the reverse voltage should be larger.
Step three: Test the output circuit
This step includes testing the reverse current and output voltage of the detection tube.
• Test the sense tube for reverse current: We connect the digital power supply to the tube sandwiched between the base of the transistor and the negative terminal of the output, set the multimeter to measure current, and note the instrument reading. Under normal circumstances, the reverse current is less than 1 uA.
• Test the output voltage: We test the voltage at the output port by connecting a digital power supply and a multimeter to make sure it is as expected. During the test, we should gradually increase the current and record its changes. The correct output circuit should be able to produce a light signal that causes the LED light to light up.
The 4N35 is available in a 6-pin dual in-line package and tube packaging. Its package diagram is as follows:
4N25 and 4N35 are common optocouplers, the main differences between them are as follows:
1. Optoelectronic characteristics: Due to the different output circuits, 4N25 and 4N35 differ slightly in their optoelectronic characteristics. 4N35's photosensitive transistor has a higher collector-emitter (CE) current gain, so it may be more sensitive to input optical signals than 4N25.
2. Package type: 4N25 and 4N35 are available in a variety of different package forms, including direct insertion type (DIP) and surface mount type (SMD), etc.. When choosing, we need to decide which package form to use according to the specific installation requirements and application environment.
3. Input and output types: 4N25 and 4N35 are both optocouplers, whose input and output terminals are realized through photodiodes and photosensitive transistors to achieve electrical - optical - electrical optical coupling conversion. However, the two output types are different. 4N25 has an output, usually output a phototransistor collector; and 4N35 has an output and a base, usually output a phototransistor collector and a higher gain switching transistor (usually NPN type) base.
Frequently Asked Questions
1. What does a 4N35 do?
The 4N35 is an optocoupler for general purpose application. It consists of gallium arsenide infrared LED and a silicon NPN phototransistor. What an optocoupler does is to break the connection between signal source and signal receiver, so as to stop electrical interference.
2. What is 4N35 used for?
4N35 can be used in AV conversion audio circuits. Broadly it is widely used in electrical insulation for a general optocoupler. See the internal structure of 4N35 above.
3. What is equivalent to 4N35 optocoupler?
4N35 replacement and equivalent optocouplers are 4N36, 4N37, 4N25, 4N26, 4N28, PC816, PC817 , 4N27, 4N36 & H11Ax series.
4. What is the difference between PC817 and 4N35?
The PC817 is a photo-transistor type of optocoupler while the 4N35 is a photo-triac optocoupler. The photo-transistor devices are primarily used in DC circuits, whereas the photo-triac devices allow control of AC-powered circuits.
