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# Make the full I-V characteristics curve for the ideal PN junction diode. Define dynamic resistance in the forward biased state.

Last updated date: 15th Jul 2024
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Hint:The resistance offered by the p-n junction diode when AC voltage is applied. When a forward biased voltage is applied to a diode that is connected to the AC circuit, this type of resistance is called Dynamic resistance.

When forward biased voltage is applied to the p-n junction diode, the width of depletion decreases. However the depletion region cannot be vanished completely. There exists a thin depletion layer or depletion region in the forward bias.

Therefore, thin depletion layers and atoms in the diode offer some resistance to electric current. This type of resistance is called forward resistance.

In forward biased p-n junction, based on diode there are two types of resistance takes place,
Static resistance or Direct current: DC is nothing but, the flow of charges that is free of electrons or holes through a conductor. Static resistance is defined as the ratio of DC voltage across diodes to the DC current.Direct current resistance is defined by, DC Voltage by DC current,
${R_f} = \dfrac{\text{DC voltage}}{\text{DC current}} = \dfrac{{{V_f}}}{{{I_f}}}$

Dynamic resistance or Alternating current: An electric current which periodically reverses direction and changes its magnitude with time in contrast to direct current, which flows in only one direction. Ac is used to deliver power to houses, offices etc. Alternating resistance is defined as, change in voltage by change in current. Alternating resistance,
${r_f} = \dfrac{\text{change in voltage}}{\text{change current}} \\ \therefore {r_f} = \dfrac{{\Delta {V_f}}}{{\Delta {I_f}}}$

Note:In this type of junction diode, forward bias of the voltage is applicable only in the p-n junction diode. When the p type and n type semiconductors are joined then it is called a p-n junction diode. In a p-n junction diode there are two electrons semiconductor devices.