Chapter 3: Diode Approximations

1
Chapter 3Diode Approximations

• There are three (3) Diodes Approximations
• Ideal (1st-Approximation)
• Second approximation
• Third Approximation
• For the 1st-approx. assume the diode drop voltage
  is zero (Perfect closed switch)
• For the 2nd-approx. assume the diode drop voltage
  of 0.7 volts
• For the 3rd approx. assume the diode drop
  voltage of 0.7 volt and consider the forward bulk
  resistance of the diode
• Vd 0.7 V Id x Rb (3-5)
• Ignoire bulk resistance of the diode if Rb lt 0.01
  Rth

2
Forward Bulk Resistance

• Calculate the Bulk Resistance (Rb) from the
  formula given below
• Rb (V2 V1)/(I2 I1)
• Forward bulk resistance (Rb) is very small less
  than 1 Ohms or 10
• Ohms. The bulk resistance is the dynamic
  resistance while current
• pass through the diode, but static
• resistance that usually measured by meter is
  relatively small
• compare to the bulk resistance.
• The reverse resistance of the diode is very
  large greater than
• 1 M-ohms.

3
Example of 2nd-approximation
4
Thevenins Equvalect Circuit
5
(No Transcript)