## Electronic Devices

# Intrinsic Semiconductor, Extrinsic Semiconductor, p-n Junction

- A semiconductor in pure form is called INTRINSIC SEMI CONDUCTOR

Ex: Si, Ge,.. - At any temperature the number of holes in valance band and the number of free electrons in conduction band are equal (n
_{e}= n_{h}). - For intrinsic semiconductors, the fermi energy level lies exactly at the middle of the forbidden band.
- Ie = neAVe (current due to electrons)
- Ih = neAV
_{h}(current due to holes) - The total current at any instant in semi-conductor is I = I
_{e}+ I_{h} - HALF WAVE RECTIFIER converts half cycle of applied A.C into DC
- When a half wave rectifier is used to convert 'n' Hz A.C into D.C., then the number of pulses per second present in the rectified voltage is 'n' only.
- HALF WAVE RECTIFIER

\tt EFFICIENCY\left(\eta\right)=\frac{DC\ Power\ output}{AC\ Power\ input} - \tt EFFICIENCY\left(\eta\right)=\left[\frac{0.406\times R_{L}}{r_{F}+R_{L}}\right]\times 100\%
- n
_{max}= 40.6% for an ideal diode. - Rectification is the process of converting AC to DC
- FULL WAVE RECTIFIER converts the whole cycle of applied input A.C signal into D.C signal.
- When a full wave rectifier is used to convert ‘n’ Hz A.C into D.C, then the no of pulses per second present in the rectified voltage is 2n
- Efficiency of full wave Rectifier,

\tt Efficiency\left(\eta\right)=\frac{DC\ Power\ output}{AC\ Power\ output} - \tt EFFICIENCY\left(\eta\right)=\left[\frac{0.812\times R_{L}}{r_{F}+R_{L}}\right]\times 100\%=81.2\%
- n
_{max}= 81.2% for an ideal diode. - With the increase of temperature, the ratio \tt \frac{n_e}{n_h} for n-type decreases, but \tt \left(\frac{n_e}{n_h}>1\right)
- As the temperature increases, the ratio \tt \frac{n_e}{n_h} for P-type increases, but \tt \left(\frac{n_e}{n_h}<1\right)

### View the Topic in this video From 00:16 To 14:34

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1. Forward resistance of diode Junction = \frac{\Delta V}{\Delta I}

2. Peak value of current is halfwave Rectifier I_{m} = \frac{V_{m}}{r_{f} + R_{L}}

3. Peak value of current is I_{m} = \frac{V_{m}}{r_{f} + R_{L}} in full wave Rectifier.

4. Dynamic output resistance R_{o} = \left[\frac{\Delta V_{CB}}{\Delta i_{c}}\right]_{i_{e} = {\tt constant}}

5. Dynamic input resistance R_{i} = \left[\frac{\Delta V_{BE}}{\Delta I_{B}}\right]_{V_{CE} \rightarrow {\tt constant}}