ClassX Video Lessons Youtube Channel The Engineering Mindset How Optocouplers work – opto-isolator solid state relays phototransistor
Optocouplers, also known as opto-isolators or photo couplers, are fascinating components used to control circuits while keeping them electrically isolated. Let’s dive into how they work and how you can design simple circuits using them.
An optocoupler is an integrated electronic component that typically has four pins. These pins are labeled as follows: pin one is the anode, pin two is the cathode, pin three is the collector, and pin four is the emitter. A small circular indentation near pin one helps identify the pins, and the part number on the body helps you find the manufacturer’s datasheet.
Essentially, an optocoupler acts as a solid-state relay, connecting two separate electronic circuits. Circuit one connects across pins one and two, while circuit two connects across pins three and four. This setup allows circuit one to control circuit two, enabling signal transfer while keeping the circuits electrically isolated. This isolation is crucial for protecting circuits from voltage spikes and noise, ensuring that disturbances in one circuit do not affect the other.
By adding components like transistors to the output of circuit two, you can control higher voltages and currents, automating circuit control. While there are various types of optocouplers, we’ll focus on the basic phototransistor version.
The symbol for a phototransistor optocoupler includes an LED symbol on the left and a transistor-like symbol on the right. This is because it uses a modified transistor known as a phototransistor. Unlike a standard transistor, which requires a base pin to control current flow, the phototransistor is activated by light from the internal LED.
In a typical transistor circuit, a small voltage applied to the base pin allows current to flow, turning on a connected light. The phototransistor in an optocoupler works differently. It blocks current in the main circuit until light from the LED hits it, turning it on and allowing current to flow. Thus, by controlling the LED, you can control the flow of current in circuit two.
Inside the phototransistor, layers of semiconductor materials, known as n-type and p-type, are sandwiched together. These materials are made from silicon mixed with other elements to alter their electrical properties. The n-type has extra electrons, while the p-type has fewer, creating spaces for electrons to move into.
When the LED is off, an electrical barrier prevents electron flow. However, when the LED is on, it emits photons that hit the p-type material, knocking electrons across the barrier into the n-type material, allowing current to flow. This mechanism enables control of a secondary circuit using just a beam of light.
Conductors like copper allow electrons to flow freely, while insulators like rubber prevent electron flow. Semiconductors, however, can act as both conductors and insulators. They have a valence shell with too many electrons to be conductors, but the conduction band is close enough that external energy, such as photons, can free electrons, allowing them to conduct electricity.
Let’s explore a basic circuit using a light-dependent resistor (LDR) and a white LED. The LDR changes its resistance based on light exposure, with high resistance in darkness and low resistance in bright light. A white LED requires 3 volts and 20 milliamps to operate.
In our primary circuit, we use a 9-volt battery, a switch, and a resistor to control the white LED. The resistor value is calculated by subtracting the LED voltage from the supply voltage, resulting in a 300-ohm resistor. To slightly reduce current, we use a combination of 330-ohm and 22-ohm resistors.
On the secondary side, a red LED indicates circuit activity. The LDR, placed opposite the white LED, provides about 70 ohms of resistance when exposed to light. We calculate the resistor for the red LED by subtracting the LED voltage and LDR voltage drop from the supply voltage, using two 150-ohm resistors.
To prevent ambient light interference, we cover the LDR and LED with electrical tape. Pressing the button on the primary circuit turns on the white LED, shining light on the LDR and activating the red LED on the secondary side.
We can also use infrared emitters and receivers. The infrared emitter, rated for 30 milliamps, is tested at 1.2 volts and 0.02 amps. On the primary side, a 9-volt supply powers the infrared emitter and a red LED to indicate activation. The secondary side includes a receiver LED with its own voltage drop and current requirements.
Another option is the PC817 optocoupler, which has an internal LED rated for 1.2 volts and 20 milliamps. Using a switch and a red LED for activation, we calculate resistors similarly to previous circuits. Pressing the switch activates the optocoupler, allowing current to flow and turning on the secondary side red LED.
Continue exploring the fascinating world of electrical and electronics engineering by checking out more resources and tutorials. Stay connected with us on social media and visit theengineeringmindset.com for more insights.
Design a simple circuit using an optocoupler to control an LED. Use a breadboard, resistors, and a phototransistor optocoupler. Experiment with different resistor values to see how they affect the LED’s brightness. Document your findings and share them with your classmates.
Utilize circuit simulation software like LTSpice or Tinkercad to model an optocoupler circuit. Simulate the effect of turning the internal LED on and off, and observe how it controls the connected circuit. Present your simulation results in a short report.
Research different types of optocouplers, such as phototransistor, photodiode, and phototriac optocouplers. Prepare a presentation comparing their functionalities, advantages, and typical applications. Share your presentation with the class to enhance collective understanding.
Create a DIY experiment to demonstrate the isolation properties of optocouplers. Use a multimeter to measure voltage levels in both circuits when the optocoupler is active and inactive. Analyze how the optocoupler prevents electrical interference between circuits.
Analyze a real-world application of optocouplers in industry, such as in power supply units or communication systems. Write a case study detailing how optocouplers enhance system reliability and safety. Discuss your findings in a group discussion.
Here’s a sanitized version of the provided YouTube transcript:
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This is an optocoupler, which is used to control circuits. In this video, we will learn how they work and how to design some simple optocoupler circuits.
Optocouplers are integrated electronic components that look something like this. They are also known as opto isolators, optical isolators, and photo couplers. In this version, we have the main body with four pins: pin one is the anode, pin two is the cathode, pin three is the collector, and pin four is the emitter. There is also a small circular indentation in the body next to pin one, which helps identify the different pins. Additionally, there is some text on the body that indicates the part number, which we use to identify the type of optocoupler and find the manufacturer’s datasheet.
This device is essentially a solid-state relay that interconnects two separate electronic circuits. Circuit one is connected across pins one and two, while the second circuit is connected across pins three and four. This allows circuit one to control circuit two, enabling signal transfer while keeping the two circuits electronically isolated from each other. This isolation is important because voltage spikes and noise on one circuit will not disrupt the other circuit, thus protecting both circuits. The optocoupler also ensures that electrons flow in only one direction due to the semiconductor materials inside, allowing the two circuits to use different voltages and currents.
We can enhance the capabilities of the device by adding another component, such as a transistor, to the output of circuit two. This allows us to control even higher voltages and currents and automate circuit control. There are several variations of optocouplers, but we will focus on the basic phototransistor version for this video.
When we look at the symbol for this optocoupler, we see an LED symbol on the left and a symbol that resembles a transistor on the right. This is because it is a modified version of a transistor known as a phototransistor. The terminals are named collector and emitter, similar to a normal transistor, but we are missing the base pin.
In a standard transistor circuit, we have a main circuit and a control circuit. The transistor blocks current in the main circuit, keeping the light off. When we apply a small voltage to the base pin, it turns the transistor on, allowing current to flow in the main circuit, thus turning the light on.
The transistor within the optocoupler works slightly differently. It also blocks current in the main circuit but acts as a receiver when the light emitted from the LED hits the transistor. This turns it on, allowing current to flow in the main circuit. So, when circuit one is complete, the LED turns on, shining a beam of light that activates the transistor, allowing current to flow in circuit two. We control this by turning the internal LED on and off. The phototransistor acts like an insulator, blocking current flow unless exposed to light.
The LED and the transistor are both enclosed within the case, so we can’t see them, but we can observe how they work with simple circuits, which we will learn to make later in this video.
So, how does the LED turn the transistor on? Inside the phototransistor, we have different layers of semiconductor materials: n-type and p-type, which are sandwiched together. Both types are made from silicon but mixed with other materials to change their electrical properties. The n-type has extra electrons that are free to move, while the p-type has fewer electrons, creating empty spaces for electrons to move into.
When these materials are joined, an electrical barrier develops, preventing electron flow. However, when the LED is turned on, it emits photons that hit the p-type material, knocking electrons across the barrier into the n-type material. This allows current to develop. When the LED is turned off, the photons stop, and current in the secondary side stops as well.
This mechanism allows us to control a secondary circuit using just a beam of light. This works because of the semiconductor material. In normal wires, copper acts as the conductor and rubber as the insulator. Electrons can flow through copper but not through rubber.
Looking at the basic model of a metal conductor, we have a nucleus at the center surrounded by orbital shells that hold the electrons. Each shell can hold a maximum number of electrons, and an electron needs a certain amount of energy to be accepted into each shell. The outermost shell is known as the valence shell. A conductor typically has one to three electrons in its valence shell, allowing electrons to break free and move to other atoms.
In contrast, an insulator has a packed outermost shell, leaving little room for electrons to join. The conduction band is far away, so electrons cannot escape, preventing electricity from flowing through the material.
Semiconductors are different; they have one too many electrons in their valence shell to be conductors, so they act as insulators. However, the conduction band is close enough that if we provide external energy, such as a photon, some electrons can gain enough energy to jump into the conduction band and become free. Thus, a semiconductor can act as both an insulator and a conductor.
The first circuit we will look at uses a light-dependent resistor (LDR) and a white LED. The LDR varies its resistance based on light exposure. In darkness, it has high resistance, while in bright light, it has low resistance. This white LED is rated for 20 milliamps and requires 3 volts to achieve that current.
When testing the LDR, we find that in dim light, it has around 40 kilo-ohms of resistance, while in complete darkness, it can reach around nine mega-ohms. However, when exposed to the white LED, its resistance drops to around 66 ohms.
For the primary circuit, we need a white LED with a voltage drop of 3 volts and a current of 0.02 amps. We will control this with a switch and use a 9-volt battery to power the circuit. The resistor is calculated by subtracting the LED voltage from the supply voltage, giving us a voltage drop across the resistor. The circuit current is 0.02 amps, leading to a resistor value of 300 ohms.
To reduce the current slightly, I will use a 330-ohm and a 22-ohm resistor, which combine to form 352 ohms of resistance. After placing the components into the circuit, it looks like this. When I press the switch, the LED illuminates.
On the secondary side, we have a red LED with a voltage drop of 2 volts and a current of 0.02 amps to indicate that the circuit is working. The LDR is placed opposite the white LED, providing a resistance of approximately 70 ohms when exposed to light.
To find the resistor for the LED, we subtract the LED voltage and the voltage drop across the LDR from the supply voltage. This gives us a required resistor value, which I will achieve using two 150-ohm resistors.
To prevent ambient light from activating the circuit, we will use electrical tape to cover both the LDR and the LED. This way, when I press the button on the primary circuit, the white LED turns on, shining light onto the LDR, which activates the red LED on the secondary side.
For the next circuit, we will use an infrared emitter and receiver. The infrared emitter is rated for 30 milliamps, but I will use less current. Testing the LED shows that at 1.2 volts, it has a current of 0.02 amps.
On the primary side, we have a 9-volt supply and an infrared emitter. A red LED is included to indicate when the circuit is activated, as we cannot see the infrared LED. The calculations for the resistors are similar to the previous circuit.
When I connect the components, pressing the switch turns on the red LED and activates the infrared emitter. On the secondary side, we have the receiver LED, which also has a voltage drop and current requirement.
The third circuit uses a PC817 optocoupler. The input side has an internal LED rated for 1.2 volts and 20 milliamps. We will again use a switch and a red LED to indicate activation. The calculations for the resistors are similar to the previous circuits.
When I press the switch, the red LED turns on, and the optocoupler activates the secondary side, allowing current to flow and turning on the secondary side red LED.
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This version maintains the technical content while ensuring clarity and readability.
Optocouplers – Devices that transfer electrical signals between two isolated circuits using light waves to provide coupling with electrical isolation between the input and output. – Optocouplers are often used in power supply circuits to isolate the low voltage control side from the high voltage power side.
Circuits – Closed paths through which electric current flows or may flow. – In our lab, we designed circuits to test the efficiency of different semiconductor materials.
Phototransistor – A semiconductor device that converts light into electrical current, functioning as a light-sensitive transistor. – The phototransistor in the sensor module detects changes in light intensity to trigger the alarm system.
Semiconductors – Materials with electrical conductivity between that of a conductor and an insulator, used in the manufacture of electronic components. – Silicon is one of the most commonly used semiconductors in the production of integrated circuits.
Conductors – Materials that allow the flow of electrical current with minimal resistance. – Copper is widely used in electrical wiring due to its properties as an excellent conductor.
Insulators – Materials that resist the flow of electric current, used to protect or isolate electrical components. – The rubber coating on electrical wires acts as an insulator to prevent accidental shocks.
Voltage – The electrical potential difference between two points in a circuit, driving the flow of current. – We measured the voltage across the resistor to determine the power consumption of the circuit.
Current – The flow of electric charge in a circuit, typically measured in amperes. – The current flowing through the LED was adjusted to ensure optimal brightness without damaging the component.
Resistance – The opposition to the flow of electric current in a material, measured in ohms. – By increasing the resistance in the circuit, we were able to reduce the current to a safe level for the components.
Light – Electromagnetic radiation visible to the human eye, often used in electronic devices for signaling and communication. – The light emitted by the LED indicator provides a visual confirmation that the device is powered on.
