Current-voltage characteristics
The following assumptions are involved when deriving ideal current voltage characteristics of BJT
- Low level injection
- Uniform doping in each region with the abrupt junctions
- One dimensional current
- Negligible recombination generation in the space charge regions
- Negligible electric fields outside the space charge regions.
It is important to characterize minority diffusion currents induced by the injection of carriers. With regard to the PN junction diode, a key relation is diffusion equation.
![2466_current voltage characteristics.png](https://www.expertsmind.com/../CMSImages/2466_current voltage characteristics.png)
A solution of this equation is given below, and two boundary conditions are used to solve and find C1 and C2.
![1756_current voltage characteristics1.png](https://www.expertsmind.com/../CMSImages/1756_current voltage characteristics1.png)
The following equations apply to emitter and collector region, respectively, and origins 0, 0', and 0'' apply to base, collector, and emitter.
![534_current voltage characteristics2.png](https://www.expertsmind.com/../CMSImages/534_current voltage characteristics2.png)
![1919_current voltage characteristics3.png](https://www.expertsmind.com/../CMSImages/1919_current voltage characteristics3.png)
A boundary condition of emitter is given below:
![2456_current voltage characteristics4.png](https://www.expertsmind.com/../CMSImages/2456_current voltage characteristics4.png)
The values of constants A1 and B1 are zero because of the following conditions of emitter and collector regions as
and
.
![435_current voltage characteristics5.png](https://www.expertsmind.com/../CMSImages/435_current voltage characteristics5.png)
Because A1 = B1 = 0, values of ΔnE(0'') and Δnc(0') are A2 and B2, respectively.
![2231_current voltage characteristics8.png](https://www.expertsmind.com/../CMSImages/2231_current voltage characteristics8.png)
Expressions of IEn and ICn can be evaluated.
![281_current voltage characteristic9.png](https://www.expertsmind.com/../CMSImages/281_current voltage characteristic9.png)
Because insignificant recombination takes place, the second derivative of ΔpB(x) is zero. There is therefore a linear relationship among excess hole density and x.
![1353_current voltage characteristic10.png](https://www.expertsmind.com/../CMSImages/1353_current voltage characteristic10.png)
Following are the boundary conditions of ΔpB.
![1157_current voltage characteristics11.png](https://www.expertsmind.com/../CMSImages/1157_current voltage characteristics11.png)
Substitute into above linear relation.
![953_current voltage characteristics12.png](https://www.expertsmind.com/../CMSImages/953_current voltage characteristics12.png)
With this result, now derive value of IEp.
![88_current voltage characteristics13.png](https://www.expertsmind.com/../CMSImages/88_current voltage characteristics13.png)
Use expressions of IEp, IEn, ΔpB(0), and ΔpB(W) to develop an expression of emitter current.
![1014_current voltage characteristics14.png](https://www.expertsmind.com/../CMSImages/1014_current voltage characteristics14.png)
Likewise, an expression of collector current is derived.
![636_current voltage characteristics15.png](https://www.expertsmind.com/../CMSImages/636_current voltage characteristics15.png)
An expression of base current is found with previous results.
![797_current voltage characteristics16.png](https://www.expertsmind.com/CMSImages/797_current%20voltage%20characteristics16.png)
Punchthrough
When base collector voltage reaches a certain value, base collector depletion region boundary meets the base-emitter depletion region boundary. When in this state transistor effectively has no base. The device loses all gain when in this state.
Email based Electronics Devices and circuits assignment help - homework help at Expertsmind
Are you searching Electronics Engineering assignment help expert for help with Current–voltage characteristics of Ebers Moll Model questions? Current–voltage characteristics of Ebers Moll Model topic is not easier to learn without any external help? We at www.expertsmind.com offers free lecture notes for Electronics Devices and circuits assignment help and Electronics Devices and circuits homework help. Live tutors are available 24x7 hours for helping students in their Current–voltage characteristics of Ebers Moll Model related problems. We provide step by step Current–voltage characteristics of Ebers Moll Model question's answers with 100% plagiarism free content. We prepare quality content and notes for Current–voltage characteristics of Ebers Moll Model topic under Electronics Devices and circuits theory and study material. These are avail for subscribed users and they can get advantages anytime.
Why Expertsmind for assignment help
- Higher degree holder and experienced experts network
- Punctuality and responsibility of work
- Quality solution with 100% plagiarism free answers
- Time on Delivery
- Privacy of information and details
- Excellence in solving electronics engineering questions in excels and word format.
- Best tutoring assistance 24x7 hours