diode load line and several types
pp 42-48
Example 3.3.1:
Give the characteristic curve of a diode. To obtain the statistical
Library resistance at point A and the dynamic resistance at point B.
ln (mA)
100 90 80 70 60 50 40
0,2 0,4 0,6 0,8 0,9 1 1,2 1,4 1,51,6 VA
Solution
The static resistance at point A is:
Figure 3.3.5.Charaktiristiki curve of the diode in the example
The dynamic resistance at point B is:
3.3.2 Straight burden
In paragraph 3.2.1 stated that to resolve a circuit containing a diode proper polarization, using the equivalent circuit. But there is a second way to solve this circuit, which is not graphic and computing, and is as follows:
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KPYSTALLODIODOI
In a circuit of a diode D connected in correct polarity of direct current source to V | and load resistor RL. Emphasis is also the characteristic of the diode (Figure 3.3.6).
(A) (b)
Figure 3.3.6. Graphic resolution. (A) Circuit (b) A Straight burden
If VD is the voltage across the diode current and lD circuit, applying the rule Kirchnoff trends will be:
3.3.8
Replacing it will be:
V | = VD + ID Rl ^ VD = V; - ID RL
3.3.9
Equation (3.3.8) is a linear equation of first instance and represents the change in voltage across the diode VD as a function of change of current ID. Schematically this equation is represented by a straight line, called the load line (Figure 3.3.6v).
To find the intersection of the straight line with the burden of stress should be put in relation (3.3.9), ID = 0 so:
3.3.10
That is, the intersection of the line load on the horizontal axis
trends is the point where the voltage is equal to the voltage source.
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Example 3.3.2
To determine the operating point (VQ, IQ) in the following circuit when
given the characteristic of the diode in Figure 3.3.7.
WmA)
To find the intersection of the straight load with shaft currents, should enter the relationship (3.3.9), VD = 0 so:
3.3.11
These values are given in relations (3.3.10) and (3.3.11) determine the line of load mapped in Figure 3.3.6. The same shape can be etched and the characteristic curve of the diode. The intersection of the characteristic with the line load Q is a point called the resting point or operating point of the circuit. The voltage and current VQ IQ is the voltage and the bias current of the diode, respectively.
Figure 3.3.7
Solution
We design the line load. This will intersect the axis of trends in Section VD = 10V and axis currents at point
10V
= 2,22 mA
The intersection of the straight load with the characteristic curve is the point Q, whose coordinates are IQ, VQ. So resting point (function) is VQ - 2,8 Volt, IQ - 1,6 mA.
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KPYITAMOAIOAOI
Ij (mA)
Figure 3.3.8 Finding serenity point (operating)
Example 3.3.3
For the above circuit to calculate the diode and ischei's
in load.
Solution
The power consumption in the diode is:
pD = IQ 'VQ = 1.6 mA x 2,8 V = 4,48 mW.
The power consumption in the load is:
PL-IQ RL = (1,6 x 10-3) 2 x 2.8 x 103 = 7,168 mW x 10-3 = 7,168 mW
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3.3.3 Trade routes
The construction of diodes - PN contacts made with various techniques
that will be analyzed in the course of electronic technology.
Examples are the development of contact with the alloy contact, the e-
pafi diffusion and development of a method of requisition.
Annex of the book are given technical brochures pathways as-
that described by the manufacturers. The values given for the main characteristics of diodes are maximum levels
(Ratings) beyond which the diode is destroyed:
1. Maximum forward current (IF MAX)
2. Maximum voltage at the proper time (VF MAX)
3. Maximum reverse voltage at the time (VRRM, VBR)
4. Maximum reverse current IR I0 or
5. High power diode PMAX
The diodes are described with some codes that specify the type of semiconductor, eg silicon or germanium, the series, etc. These codes include letters of the Latin alphabet and numbers. The table features are indicative of some passages:
Passage
'F MAX (A)
VF MAX (V)
VRRM (V)
IO, IR (A)
1N 4001
Table 3.3.1 Characteristics of trade routes
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SUMMARY 3.1 - 3.3
• A diode conducts when the voltage at the anode is more positive than the cathode voltage and behaves like a closed switch. When the anode voltage is from Negative voltage of the diode cathode is polarized upbringing, does not conduct and behave like an open switch.
• When creating contact PN created an area called stripping area, with positive charges in the N-type semiconductor and negative charges in the semiconductor type R. The voltage generated in the region called stripping BARRIER voltage (V0).
• The characteristic curve of a PN diode is divided into three regions: a region of good wear characterized by small positive trend
positive and large current (mA or A) after the threshold voltage or knee.
b area reverse direction, characterized by negative
negative voltage and low current (mA or nA). c decay region is characterized by the (negative) voltage Zener and large currents.
• The DC resistance of a PN diode is small at the proper time and a very long time in reverse.
QUESTIONS - EXERCISES 3.1 - 3.3
3.1.1. When a diode is properly biased?
3.1.2. When a diode is reverse biased?
3.1.3. Describe the creation of the stripping area.
3.1.4. Flows through a diode current of 100 mA from when it is correctly polarized voltage of 2V and current of 5 mA when it is reverse biased with a voltage
50V. To determine the correct resistance and reverse directions.
3.1.5. If a diode with an analog ohmmeter measured and shown great resistance and the correct and reverse time what happens? A) open b) is shorted c) is defective
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+
V: = 50V ^; r
Find the operating point, the graphical method, if the diode is at right syndedeni polarization resistance R =
And Z = 2000 dc source V; = 100 Volt.
3.1.12. Consider the following circuit and the characteristic of the diode. Calculate the operating point graphically.
R = 1000
3.1.6. Each diode in the circuit described below by a resistor and a voltage threshold. The diodes D1 and D2 are silicon diodes and have Vy1 = V2 = 0.7V and R = 20O and 30O R2 =. To determine the currents in the diodes when the resistance R = 1KO.
D2V
b The resistance is shorted C. The diode is shorted D. b and c
3.1.11. To establish the characteristic of a diode with the following elements:
Figure 3.3.9 Circuit activity 3.6.
3.1.7. Making the right match between the following elements: Voltage IR barrier knee voltage V0 Vy forward current IF current reverse direction
3.1.8. Silicon diode power consumption of 5W when passed over by a current of 1 A polarization in the proper time. What is the voltage across it?
3.1.9. The voltage drop at the ends of a good silicon diode is polarized correctly:
a 0,3 V c 0,3-0,7 V
5 -7 V b d 0,5-0,7 V
Note the correct price.
3.1.10. In the circuit of Figure 3.3.6, the input is V; = 25 date (vi). If the output amplitude is VL = 25V, to justify what happens:
The diode is a high
Figure 3.3.10 Circuit exercise 3.1.12.
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where K is a constant which depends on the geometry and
the semiconductor material, V0 is the potential barrier and VR is the e-
farmozomeni reverse trend.
The diode is, when reverse polarized, corresponds to a variable
capacitor whose capacity varies with the external voltage, as opposed to a capacitor whose capacitance is constant and independent of the applied voltage at the ends.
3.4 Diode choritikotitas variable (Varicap <Varactor)
As mentioned in paragraph 3.1.2, the area of stripping contact PN diode is a capacitor with "reinforcements" the two parts of the region P and N type containing negative and positive charges respectively. The capacitance of the capacitor CT is dependent on the cross section S of the diode, the length L of the region and stripping the dielectric e, according to relation (3.1.3):
3.4.1
It turns out that the capacity varies inversely CT value of the external voltage applied to the ends of the diode when connected in reverse polarity, according to relation (3.4.2) and Figure 3.4.1.
3.4.2
Ct (PF)
-> VR (V)
The diode is called a variable capacity diode <Varikap diode (Varicap) <Varactor.
Figure 3.4.1
Change in capacity diode Varicap
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