Data sheet of Diode.pptx

Data sheet of diode
Details explanation

1. Data sheet and circuit models of diode 1

2. Diode Specification Sheets Data about a diode is presented uniformly for many different diodes. This makes cross-matching of diodes for replacement or design easier. It includes: Forward Voltage (V F ) at a specified current and temperature Maximum forward current (I F ) at a specified temperature Reverse saturation current (I R  ) at a specified voltage and temperature Reverse voltage rating, PIV or PRV or V(BR), at a specified temperature 2

3. 5 . Maximum power dissipation at a specified temperature 6. Capacitance levels 7. Reverse recovery time , t rr 8. Operating temperature range Forward Bias Voltage The point at which the diode changes from no-bias condition to forward-bias condition occurs when the  electrons and holes are given sufficient energy to cross the p-n junction. This energy comes from the external voltage applied across the diode. 3

4. The forward bias voltage required for a: gallium arsenide diode 1.2 V silicon diode 0.7 V germanium diode 0.3 V Peak forward current, I FRM The maximum forward current with sine-wave operation, f ≥ 25 Hz , or pulse operation , f ≥25 Hz, having a duty cycle t p /T ≤ 0.5 . Reverse current, I R (leakage current) The current which flows when reverse bias is applied to a semiconductor junction. 4

5. Temperature Effects As temperature increases it adds energy to the diode. It reduces the required forward bias voltage for forward-bias conduction. It increases the amount of reverse current in the reverse-bias condition. Breakdown voltage, VBR Reverse voltage at which a small increase in voltage results in a sharp rise of reverse current . It is given in the technical data sheet for a specified current. Breakdown voltage 5

6. It increases maximum reverse bias avalanche voltage . Germanium diodes are more sensitive to temperature variations than silicon or gallium arsenide diodes Resistance Levels Semiconductors react differently to DC and AC currents . There are three types of resistance : DC (static) resistance AC (dynamic) resistance Average AC resistance 6

7. 7

8. 8

9. 9

10. Diode Capacitance 10

11. 11

12. 12

13. Diode Model Parameters 13

14. 14

15. Large Signal DC Model Characterized by the R/s between dc current and voltage at diode terminals Parameters used to model are I s , R s , N , BV , and IBV . I s – reverse saturation current R s - O hmic resistance of metal contacts and neutral region of diode N – emission coefficient to modify I-V characterstics of diode BV and IBV – model reverse breakdown behavior 15

16. Figure 3.1 shows the equivalent circuit of diode for large signal analysis. 16

17. Where D 1 – intenal diode R s – series resistance G min – shunt conductance ( 10 -12 mho or can be set to any non-zero value ) Hence dc-model variables are: V F –voltage across external diode terminals V D – voltage across internal terminals I D – terminal current 17

18. With these parameters and variables the large signal dc characteristics can be modeled by the following equations : F our regions of operation describe functional relationship between internal diode voltage and terminal current as : 18

19. For all above equations V t is thermal voltage given by: 19

20. To insure convergence between regions (c) and (d), it is necessary that IBV is: 20

21. 21

22. Small –signal AC- model of diode Derived from the linearized small-signal behavior of internal diode i.e : 22

23. Where CJ – junction capacitance GD – dynamic conductance CD – diffusion capacitance With all are bias dependent. Junction capacitance (CJ) can be modeled by parameters CJO, VJ, M and FC. CJO and VJ are identical to zero-bias junction capacitance C j (0) and contact potential V j of ideal diode. 23

24. M – grading exponent used to change the slope of junction capacitance vs reverse voltage ( abrapt junction diode M=0.5 but for graded junction M=0.333). FC – parameter to model the capacitance under forward bias condition. Variables for the model CJ in Farad and internal diode voltage V D are related as: 24

25. To insure equation 3.11 well behaved , FC is restricted as: 25

26. A typical C –V curve produced by above equations is given as: 26

27. The variable dynamic conductance GD is a function of internal diode voltage V D and given in three region of operations as: 27

28. The variable diffusion capacitance CD modeled by forward transient time parameter TT and the parameters I s and N in three region of operations as: 28

29. Note Above model parameters of diode have certain limitations . For some of the parameters, suggested value restrictions are given in order to insure convergence . 29

30. 30

31. Parameter Extraction 1- Forward DC characteristics I s , R s and N are parameters to model dc characteristics (large signal model) in the forward region . There are three methods to extract Three point I-V method Method which uses fixed value of R s (taken from method I)and perform linear regression data fit over the I-V curve to extract I s and N . Use fixed value of I s and perform a non-linear data fit to extract N and R s .(Useful if I R reverse leakage current is specified). 31

32. Method I Use forward-bias I-V curve where current axis is logarithmic Step-1 : Select three data points from the I-V curve as points 1, 2 and 3 Step-2 : Calculate values for R s , N and I s using equations: 32

33. 33

34. 34

35. Method II (Linear regression with fixed R s ) Step-1 : Select a value of R s from method 1 Step-2 : Perform linear regression data fit on n data points taken from I-V curve , equation 3.42. where y i and x i calculated from equation 3.43 and 3.44. Then values for b and m . Step-3 : Calculate values of I s and N from equation 3.48 and 3.49 respectively. 35

36. Consider an equation which represent the diode dc characteristics : Where I D i and V F i represent i th data point on I-V curve of diode. Assume exponential term in equation 3.39 is sufficiently large this equation will be modified as: Taking natural logarithm both side of equation 3.40 then 36

37. 37

38. Values for b and m can be found by solving the matrix equation 3.47: Then I s and N determined by : 38

39. 39 Extraction of junction capacitance parameters from C-V curve There are two methods: Method I : (Three point C-V method) – use the reverse bias plot of junction capacitance verses reverse bias voltage. Procedures : Step 1 : select a data point at the lower end of the C-V curve where voltage less than ideal V J (that is 0.8 to 1 v) Step 2 : select two data points at the upper end of C-V curve (as shown on the graph by 2 and 3). Voltages should be much greater than ideal V J .

40. 40 Step 3 : Calculate the values of M, V J , CJO and FC as:

41. 41

42. 42 II, Method II : (Linear regression with fixed V J ) – perform linear data regression data fit for the whole data point of C-V curve. Consider the relation between junction capacitance and reverse voltage: Take natural logarithm to equation 3.65 both sides:

43. 43 Values for b and m can be found by solving the matrix equation 3.47:

44. 44 The parameters CJO and M are calculated as: Procedure Step 1 : Select value V J which may be value calculated from method I . Step 2 : Perform linear regression data fit on n data points taken from the C-V curve to determine b and m . Step 3 : Calculate the values of CJO and M from equation 3.72 and 3.73 respectively and value of FC from equation 3.64.

45. 45 Steps for extracting the parameter TT are: Step 1 : From the device data sheet, determine values for the reverse recovery time t rr , the forward-bias diode current I F and the slew-rate of the current waveform di/ dt . Step 2 : Generate a function of the forward transient time TT where: Step 3 : Use Newton’s method to solve equation 3.79 for the value of TT that will set f(TT) equals to zero.

46. 46 Reverse breakdown characteristics Steps for extracting the parameters BV and IBV are: Step 1 : From the diode data sheet, determine the value of the maximum DC blocking voltage V R (max) Step 2 : Multiplying the above voltage by a constant k BV (having value ranging from 1.3 to 2) to produce breakdown voltage of: BV = k BV * V R (max) Step 3 : Calculate the value of IBV as:

47. 47 Temperature characteristics are reading assignments

48. 48