Diodes Information

Diodes
Diodes are semiconductor devices which might be described as passing current in one direction only. When the diode is connected in the forward bias arrangement the charge from source repels holes and electrons towards the junction if the voltages exceeds 0.6 - 0.7 volts then electrons crosses junction and joins with hole and current flows whereas in the reverse bias arrangement the from source attracts holes away from the junction.

Diodes can also be used as the voltage regulators, switching applications as current guides which also covers tuning devices, frequency multiplying devices and mixing devices which can be used to make logic decisions in digital circuits.

Zeners

• A zener diode is a special silicon diode
• When forward biased acts the same as an ordinary diode
• When reversed biased will conduct when the reverse voltage reaches a particular value
• The voltage drop is substantially constant as the current varies
• The voltage at which reverse conduction takes place is called the Zener voltage (VZ)
• Reverse voltage of zener diode makes it a valuable component for the regulation of the output voltage against both variation in the input voltage from an unregualated power supply or variation in the load resistance.
• The current through the zener will change to keep the voltage at within the limits of the threshold of zener action and the maximum power it can dissipate.

NOTE : The limits which are necessary for operation are that Vs > Vz, and that 1z >1zmin and less than 1zmax.

LED

As with the diode the LED must be connected in the forwad bias arrangement, this ensures the holes and electrons which cross the junction change energy levels and convert current directly into light.

Advantages of LED

• Emit light in proportion to the forward current through the diode
• Are low voltage devices that have a longer life than incandescent lamps
• physically small
• Respond quickly to changes in current (10 MHz) e.g Hi-stop light
• Shock and vibration resistant
• Low wattage
• Almost no heat generation
• LEDs have application in optical-fiber communication and diode lasers
  

Types of diode

The first diode is a semiconductor diode which could be a small signal diode of the 1N914 type commonly used in switching applications, a rectifying diode of the 1N4004 (400V 1A) type or even one of the high power, high current stud mounting types.

• Power Diodes (rectifier diodes)
  
• for higher power ratings the metal stud mount is more common