Question

3 A. Define Built in Potential in a PN Junction. With the help of diagrams explain how the built in potential is formed when no external bias is applied [2 marks] B. A rectifier circuit with four silicon diodes and the output frequency equal to twice of the input frequency. The input peak to peak voltage Vin pp = 25V, the load resistance R = 560 12. [3 marks) a. Name the circuit b. Draw the circuit diagram c. Explain the working principle of the circuit and mark the flow of current in your circuit d. Draw the input and the output waveform (mark all values)

Answer 1

3.A Define Built-in-potential in P. N Junction The built-in-potential in a p-n sjunction (semiconductor) equals the potential across the depletion region to op pon Junction interface, that prevents of electrons into the p-side and holes into the n-side. KT IM C In (NONA) V built-in = 11 V built-in Built-in potential in volts NA - P-type-accepton atom concentration type- donon atom 9 - Charges in coulombs temperature in kelvin k Boltz's man Constant > concentration of electrons K% thermal voltage = NT Neutral n-region / region Depletion, Neutral p- region 15 OOO No (Donor) ANA (Acceptor) when the p-type semiconductor and N-type semiconductor materials are first joined together a very large concentration between both side of the PN junction.

up the the Then the result is that some free electrons of the N-type semiconducton wants to fill holes in the P-type material producing negative ons, and they leave behind No (Positively change donon) on the N-side same from p-type semiconductor and they leave behind NA ( Negatively changed accenton) on the P-side. Now the change transten across PN Junction is known as diffusion. N-type material has lost electrons and p-type has lost holes, the N-type material hase become positive with respect to the p-type. Then the presence of impurity ions both side of the Junction voltage difference across the depletion region. This is also called bait-in- potential defferences. when noto no-external bias is applied then it is called (zenobias) potential. As the the cause an to = Vt dn [ NO NA Eo > is the Zero bias Junction Voltage.

and S. A rectifier circuit with tour silicon diodes the output frequency input frequency. Vpp = 25v and RL = 560s. by equal to twice of The input peak to peak voltage Full wave Bridge Rectifien Circuit Diagram D1 DA +V RL - 5602 Vout Fig - Full wave Bridge C from figure are Rectition we have seen that there are 4 diodes used in bridge from, that's why it is called full wave forsidge rectifier circuit. Here Di to Da sevies pain with only two diodes conducting current dur during each half cycle. In Positive half-cycle D, L D2 are coduct Dz & Do are non-conduct are in arrange D

when positive cycle applied to the input, then only of DIG D2 Diodes are conducted because of forward bias and Dz & Af an Diodes are off because pevense biased. The current flowing through the load is shown in the figure. In Negative Half-cycle y Dz W Dq are conduct D & De are non-conduct D4 11 her same as positive cycle. As the cunnent flow through the load is unidirectional.

Input and output wave: Output wave form Vmax=25v! maxle aut aut VLCD - 1598 & T2wt

Output current ㅠ Ideat I Imax sin awt d (wt) T Imax TE Sin wt d (wt) T to Iman X [Goswt] max X - [cos TT - Coso ( Imax x 2 Imax U Dc output voltage Imax RL 2/7 Vdc = IDC R₂ = = 3/1 Vomax = 4 x 25 = 15.91 v