Electronics - Diode Applications - 06-20-15

SEMICONUCTOR DIODE

DIODE APPLICATIONSEngr. Mervin E. Albalate6: Negative Temperature CoefficientAn increase in temperature of a semiconductor can result in a substantial increase in the number of free electrons in the material.Semiconductor materials such as Ge and Si that show a reduction in resistance with increase in temperature are said to have a negative temperature coefficient.SemiconductorTemperatureResistanceTRConductorTemperatureResistanceTR7. ZENER DIODESAZener diodeis adiodewhich allows current to flow in the forward direction in the same manner as normaldiode, but also permits it to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage or "Zenerknee voltage",

7. ZENER DIODES

7. ZENER DIODES

AZener diodeis always reverse connected.

Example8. LIGHT EMITTING DIODES (LED)A diode that will give off visible light when it is energized.The process of giving off light by applying an electrical source of energy is called electroluminescence.

8. LIGHT EMITTING DIODES (LED)

9. IDEAL DIODE:The characteristics of an ideal diode are those of a switch that can conduct current in only one direction.

9. IDEAL DIODE:

10. TEMPERATURE EFFECTS :

Temperature can have a marked effect on the characteristics of a silicon semiconductor diode as witnessed by a typical silicon diode . It has been foundexperimentally that:The reverse saturation current (IS ) will just about double in magnitude forevery 10C increase in temperature.11. DIODE TESTING :

Using the Diode Testing Function of a MultimeterA working diode would display = 0.67 A defective diode would display = OL 11. DIODE TESTING :

Using the Ohmmeter (Ohmmeter Testing)A working diode would have @ FB : relatively low resistance@ RB : relatively high resistance

12. RESISTANCE LEVELS

As the operating point of a diode moves from one region to another the resistance of the diode will also change due to the nonlinear shape of the characteristic curve. 12. RESISTANCE LEVELS1. DC or Static ResistanceThe application of a dc voltage to a circuit containing a semiconductor diode will result in an operating point on the characteristic curve that will not change with time.2. AC or Dynamic ResistanceThe application of a varying input will move the instantaneous operating point up anddown a region of the characteristics and thus defines a specific change in current and voltage .With no applied varying signal, the point of operation would be the Q-point (Q-point is derived from the word quiescent, which means still or unvarying.)3. Average AC ResistanceIf the input signal is sufficiently large to produce a broad swing such as indicated inthe resistance associated with the device for this region is called the averageac resistance. The average ac resistance is, by definition, the resistance determined by a straight line drawn between the two intersections established by the maximumand minimum values of input voltage.

12. RESISTANCE LEVELS

13. DIODE EQUIVALENT CIRCUIT:An equivalent circuit is a combination of elements properly chosen to best represent the actual terminal characteristics of a device, system, or such in a particular operating region.In other words, once the equivalent circuit is defined, the device symbol can be removed from a schematic and the equivalent circuit inserted in its place without severely affecting the actual behavior of the system.13. DIODE EQUIVALENT CIRCUIT: