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• Light Emitting Diode (LED)


  A semiconductor device that emits light when forward biased. Generally uses Gallium Arsenide Phosphide (GaAsP) and Gallium Phosphide (GaP). Light is produced as the electrons and holes are recombined and releases energy.
• LED


  • Max Forward Voltage = 1.2 V to 3.2 V depending on the device
  • Reverse Breakdown Voltage = 3 V to 10 V
  • The amount of power output translated into light is directly proportional to the forward current

  
• A true blue LED always has a high forward voltage (5v)
• A white LED is 4.1v, while Red being the lowest at 1.8v, the rest ranges from 2v-2.2v
• LEDs


  Always need a resistor in tandem to regulate the current flowing through them and protect them from damage. Unlike incandescent bulbs, LEDs are sensitive to changes in voltage and can be easily damaged if too much current flows through them. Usually with a supply of 5v a 1k ohm resistor is enough.

  
• Calculating Wavelength of an LED based on Energy

  1. Convert Bandgap Energy to Joules

  2. Use the Energy-Wavelength Relationship

  
• 7 Segment Display


  Consists of 7 rectangular LEDs which can form alphanumeric figures. LED segments are labelled 'a' to 'g'
• Common-cathode type


  All the cathodes of the diodes are tied together. All the negative sides of the LEDs (the cathodes) are connected together. It's like they're all sharing the same ground connection. When you want to light up a specific segment, you send a positive voltage to that segment while grounding the common cathode, which completes the circuit and lights up the segment.

  
• Common-anode type


  All its anodes are tied together to +5 volts and ground is used to light the individual segments. All the positive sides of the LEDs (the anodes) are connected together to a positive voltage source, usually +5 volts. To light up a segment, you connect its specific cathode to ground while supplying power to the common anode, which again completes the circuit and lights up the segment.
• How to light the number 5 in 7 segment display

  The 'a', 'f', 'g', 'c' and 'c' must be forward biased with your voltage source. Then you will connect the voltage source to the anode of those 5 segments to light them.
• Two-Color LED


  A special kind of light bulb that can shine in two different colors instead of just one. To choose which color to show, you send a signal through the wires that control each color. If you want red, you send a signal to the wire for red. If you want green, you send a signal to the wire for green. And if you want both colors, you send signals to both wires at the same time.
• Three-Color LED


  It has two leads that act as both anode and cathode. When dc current flows through one direction, it emits red light, but when the current flows in the opposite direction, the LED emits green light. With AC current, yellow light is given out as the colors are added.
• Three-Color LED with AC power

  1. The LED rapidly switches polarity, causing the LED to cycle through its primary colors at a frequency determined by the frequency of the AC power source. For example, in regions with a 60 Hz AC power supply, the LED would cycle through its colors 60 times per second.

  2. As a result of this rapid cycling, the human eye perceives the blended light emitted by the LED as continuously changing color.
• Blinking LED

  • It has two things in one package. First, there's the LED, which is like a tiny light bulb. Second, there's something called an oscillator, which is like a tiny clock that tells the LED when to turn on and off.
  • The blinking LED blinks at a certain speed, which is called the blinking frequency. For this particular blinking LED, it blinks at a frequency of 3 times per second, or 3 Hz. That means it turns on and off 3 times every second, like a very fast heartbeat.
  • When the blinking LED is on, it lets electricity flow through it, allowing light to shine. It conducts about 20 milliamps (mA) of current, which is like a tiny stream of electricity. But when it's off, it only lets a tiny bit of current flow through, about 0.9 mA, which is like a trickle of electricity.
• Voltage Multiplier


  Voltage multiplier circuits use a combination of diodes and capacitors to step up the output voltage of rectifier circuits.
• Voltage Doubler

  1. Positive Half-Cycle: D1 conducts, D2 is switched off, Capacitor C1 charges to Vm

  2. Negative Half-Cycle: D1 is switched off, D2 conducts, Capacitor C2 charges to Vm
• Zener Diode


  • A special kind of diode that can conduct electricity in the reverse direction, but only when the voltage across it reaches a certain level called the Zener voltage (Vz).
  • Reverse Bias Operation: Normally, diodes only let electricity flow in one direction, from positive to negative. But the Zener diode can also conduct electricity in the reverse direction, but only when the voltage across it reaches the Zener voltage (Vz).
  • Zener Voltage (Vz): When the voltage across the Zener diode (Vi) becomes equal to or greater than the Zener voltage (Vz), the Zener diode starts to conduct electricity in the reverse direction.
  • Zener On State: When the Zener diode is conducting electricity, the voltage across it stays constant at the Zener voltage (Vz).
  • Zener Current (IZ): The current flowing through the Zener diode (IZ) depends on the resistance in the circuit.
  • Zener Power (PZ): The power dissipated by the Zener diode (PZ) is calculated by multiplying the Zener voltage (Vz) by the Zener current (IZ).
  • Zener Off State: When the voltage across the Zener diode (Vi) is less than the Zener voltage (Vz), the Zener diode doesn't conduct electricity.

  
• Zener Resistor Values


  • Every Zener diode has a specific range of currents it needs to work properly. If the current is too low (less than Imin), the Zener won't conduct. If it's too high (more than Imax), it might get damaged.
  • We need to find the smallest resistance value for our resistor so that enough current flows through the Zener diode, but not too much to exceed the maximum current. This minimum resistance is calculated using a formula.
  • We also need to make sure the resistance isn't too high, or the Zener diode won't conduct at all. We calculate the maximum resistance using another formula.

  
• Electrical Characteristics of Zener Diodes

  The Zener potential of a Zener diode is very sensitive to the temperature of operation. The temperature coefficient can be used to find the change in Zener potential due to a change in temperature.
• Maximum Power Dissipation of Zener Diodes

  • PZmax: Maximum power dissipation in the Zener diode, typically measured in watts (W).
  • IZT : Zener diode current, the current flowing through the Zener diode, typically measured in amperes (A).
  • Vz : Zener voltage, the voltage across the Zener diode when it's in the reverse breakdown region, typically measured in volts (V).

  
• Practical Applications

  • Rectifier Circuits
  • Simple Diode Circuits
  • Zener Circuits