#electronics

Rectifiers, Filters and Applications

In a half-wave rectifier, the output frequency is:

**Rectifier applications** diode must have reverse breakdown voltage higher than peak inverse voltage, centre-tap transformer provides two opposite phase voltages for full-wave, capacitor discharges through load R_L when diode off, drift current in junction is minority carrier motion due to field, diffusion due to gradient, diode conducts when forward biased anode positive. A half-wave rectifier conducts only during the positive half-cycle of the AC input, so the output frequency remains the same as the input frequency (e.g., 50 Hz input gives 50 Hz output). Substituting values gives Equal to

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p-n Junction, Depletion Region and Diode Characteristics

The forward bias current in a diode is typically measured in:

**Depletion region** also called space-charge region, thickness typically 0.5 μm, contains no mobile carriers, only fixed ions, negative on p-side, positive on n-side, diffusion current due to concentration gradient, drift current due to field, equilibrium when J_drift + J_diff =0, voltage drop mainly across depletion region. In forward bias, the current due to majority carrier diffusion is large, typically in the milliampere (mA) range, requiring a milliammeter for measurement. Substituting values gives Milliampere (mA), which matches expected behaviour for this semiconductor device configura

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p-n Junction, Depletion Region and Diode Characteristics

The reverse bias resistance of a p-n junction diode is typically:

**Depletion region** also called space-charge region, thickness typically 0.5 μm, contains no mobile carriers, only fixed ions, negative on p-side, positive on n-side, diffusion current due to concentration gradient, drift current due to field, equilibrium when J_drift + J_diff =0, voltage drop mainly across depletion region. In reverse bias, the diode allows only a small reverse saturation current ( μ A ), resulting in a very high resistance compared to the low resistance in forward bias. Substituting values gives High, which matches expected behaviour for this semiconductor device configurat

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Rectifiers, Filters and Applications

In a full-wave rectifier, the voltage across each diode is:

**Rectifier applications** diode must have reverse breakdown voltage higher than peak inverse voltage, centre-tap transformer provides two opposite phase voltages for full-wave, capacitor discharges through load R_L when diode off, drift current in junction is minority carrier motion due to field, diffusion due to gradient, diode conducts when forward biased anode positive. In a centre-tap full-wave rectifier, each diode rectifies half the total secondary voltage, as the centre tap splits the AC input into two equal halves. Substituting values gives Half the secondary voltage, which matches ex

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Rectifiers, Filters and Applications

In a full-wave rectifier with centre-tap transformer, the output frequency for a 50 Hz input is:

**Rectifier** converts AC to DC using diode unilateral conduction, half-wave conducts only during positive half-cycle when forward biased, output pulsating DC with frequency equal to input 50 Hz, full-wave with centre-tap uses two diodes conducting alternate half-cycles, output frequency 100 Hz for 50 Hz input, 120 Hz for 60 Hz input, output voltage closer to peak with capacitor filter. A full-wave rectifier doubles the input frequency by using both half-cycles, so for a 50 Hz input, the output frequency is 50 × 2 = 100 Hz . Substituting values gives 100 Hz, which matches expected behaviour fo

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Doping, Charge Carriers and Conductivity

Which of the following is a trivalent dopant used in p-type semiconductors?

**Number of carriers** from doping: Ge crystal 4×10²⁸ atoms/m³ doped 2 ppm trivalent gives acceptor atoms 8×10²² m⁻³, holes ≈ that, for 1.5 ppm 6×10²² m⁻³, for 0.5 ppm pentavalent Si 5×10²⁸ atoms/m³ gives 2.5×10²² donors/m³. Acceptor atom effectively negative when accepts electron, donor positive when donates, but crystal neutral. Trivalent dopants (valency 3) like Boron (B), Aluminium (Al), and Indium (In) are used in p-type semiconductors to create holes. Phosphorus (P) is pentavalent. Substituting values gives Aluminium, which matches expected behaviour for this semiconductor device configu

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p-n Junction, Depletion Region and Diode Characteristics

In a rectifier circuit, the diode conducts when it is:

**Diode characteristics** forward bias reduces barrier, width of depletion region decreases, resistance low ~10-100 Ω, current primarily due to majority diffusion, exponential I = I_s(e^{eV/kT}-1), reverse bias widens depletion region, resistance high ~MΩ, dominant current drift due to minority carriers, reverse saturation current small μA-nA, typically 10⁻⁶ A, increases sharply at breakdown Zener/avalanche. A diode conducts in forward bias (p-side positive, n-side negative), allowing current to flow through the load, which is the basis of rectification in both half-wave and full-wave circuits

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Semiconductors, Types and Energy Bands

Which of the following is an elemental semiconductor?

**Energy bands in semiconductors** consist of valence band filled at 0 K and conduction band empty, gap E_g small ~1 eV (Si 1.1 eV, Ge 0.7 eV), insulators large gap >3 eV (C diamond 5.4 eV), conductors overlapping. Intrinsic semiconductor at 0 K behaves as insulator because no thermal excitation, at T>0 K electrons jump to conduction band leaving holes, conductivity increases with temperature. Elemental semiconductors are pure elements like Si and Ge, while compound semiconductors (e.g., GaAs, CdS) consist of multiple elements. Among the options, Ge is elemental. Substituting values gives Ge,

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Rectifiers, Filters and Applications

In a half-wave rectifier, the output voltage appears across the load during:

**Capacitor filter** purpose to reduce ripple, capacitor charges to peak during diode conduction and discharges through load during non-conduction, time constant τ = R C, larger RC less ripple, ripple reduced by using capacitor or LC filter, output of half-wave without filter is pulsating half sinusoids, full-wave without filter is two half sinusoids per cycle. A half-wave rectifier conducts only during the positive half-cycle of the AC input, allowing current through the load only in that period, producing a pulsating output for half the cycle. Substituting values gives Positive half-cycle, w

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p-n Junction, Depletion Region and Diode Characteristics

The reverse saturation current in a p-n junction diode is typically in the order of:

**Diode characteristics** forward bias reduces barrier, width of depletion region decreases, resistance low ~10-100 Ω, current primarily due to majority diffusion, exponential I = I_s(e^{eV/kT}-1), reverse bias widens depletion region, resistance high ~MΩ, dominant current drift due to minority carriers, reverse saturation current small μA-nA, typically 10⁻⁶ A, increases sharply at breakdown Zener/avalanche. The reverse saturation current, due to minority carrier drift, is very small and typically in the microampere ( μ A ) range, independent of applied voltage until breakdown. Substituting va

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p-n Junction, Depletion Region and Diode Characteristics

The dynamic resistance of a diode is defined as:

**Depletion region** also called space-charge region, thickness typically 0.5 μm, contains no mobile carriers, only fixed ions, negative on p-side, positive on n-side, diffusion current due to concentration gradient, drift current due to field, equilibrium when J_drift + J_diff =0, voltage drop mainly across depletion region. Dynamic resistance ( r_d ) is the ratio of a small change in voltage ( Δ V ) to the corresponding small change in current ( Δ I ), i.e., r_d = Δ V / Δ I , reflecting the diode's behavior under small signal variations. Substituting values gives Δ V / Δ I, which matches exp

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Rectifiers, Filters and Applications

The ripple in a rectifier output is reduced by using:

**Capacitor filter** purpose to reduce ripple, capacitor charges to peak during diode conduction and discharges through load during non-conduction, time constant τ = R C, larger RC less ripple, ripple reduced by using capacitor or LC filter, output of half-wave without filter is pulsating half sinusoids, full-wave without filter is two half sinusoids per cycle. A capacitor filter smooths the pulsating DC output by charging during peaks and discharging during troughs, reducing AC ripples to provide a steadier DC voltage. Substituting values gives Capacitor, which matches expected behaviour for

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