Diode Circuits and Applications Questions and Answers

Answer: C

Current flows in the secondary only on one half cycle, so a net direct component magnetises the core and pushes it towards saturation, wasting capability and increasing loss. The primary's ripple, the available voltage and the ripple frequency are all separate matters. Any winding carrying unidirectional current biases its core, which is why full-wave and bridge arrangements are preferred at anything above the smallest powers. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: D

At low voltage the forward drops matter proportionally more, so a bridge using Schottky diodes minimises the loss while keeping the voltage rating modest. A half-wave circuit wastes half the cycle and magnetises the core. Silicon diodes cost twice the drop of Schottkies. And a doubler is for the opposite case, high voltage at low current. Which imperfection dominates depends on the operating point, and at five volts a 0.4 V saving per diode is worth having. The parameter that varies and the parameter that does not are worth naming before any substitution is attempted.

Answer: A

A multiplier reaches a high voltage from a modest transformer, and its poor regulation hardly matters when the load is small and steady - which is why photomultiplier and cathode-ray supplies use them. Schottkies have low voltage ratings, and both remaining options need a transformer wound for the full output voltage. Choosing a topology means matching its weakness to something the application does not need. The shared properties explain why these schemes form a family, and the differences explain why more than one exists.

Answer: B

As the diode recovers, the circuit's inductance can produce a sharp overvoltage, and a resistor and capacitor across it absorb that energy. It does nothing for the forward drop, does not change the recovery time itself, and current sharing needs series resistors instead. A fast switching event in an inductive circuit always produces a transient, and a snubber is the standard way to give that transient somewhere to go. Framing the question as which quantity the change acts upon makes the answer follow without calculation.

Answer: C

During recovery reverse current flows while reverse voltage is already present, so the product is real dissipation, and it recurs every switching cycle. The forward drop is not involved once conduction has ceased, and the capacitance contribution is small by comparison. Any overlap of current and voltage in a switching device is loss, and it is why recovery time matters more as the switching frequency rises. A single measurement chosen to respond to the one asymmetry beats several that respond to shared behaviour.

Answer: D

Dynamic resistance in breakdown is a Zener specification, since an ordinary rectifier is never operated there and would be destroyed if it were. The other three are standard rectifier ratings covering reverse blocking, brief forward overload and thermal limits. A parameter that only makes sense in a region the device is not designed for is a reliable sign that it belongs to a different device.

Answer: A

All three are correct, and together they are the entire design procedure: the first sizes the resistor from one worst-case corner, the second sizes the diode from the other, and the third states what sets the quality of the result. Any design bounded by two corners needs both checked, and quoting only the nominal condition is how a regulator comes to fail at one extreme.

Answer: B

The first three are correctly paired and the fourth is not, so three match. Rectification efficiency measures the fraction of input power appearing as direct output; the remainder is largely in the ripple rather than dissipated as heat. Each figure of merit isolates one aspect of the same waveform, and knowing what each is a ratio of is what makes them comparable across topologies.

Answer: C

A few picofarads is a low impedance at hundreds of megahertz, so signal leaks straight through a diode that is supposed to be blocking, which is why switching diodes for radio work are specified for low capacitance. The forward drop, the thermal behaviour and the leakage are all unaffected by it. A parasitic that is negligible at one frequency and dominant at another is the normal situation, and the only question is where the crossover lies.

Answer: D

A PIN diode's thick intrinsic layer makes it behave as a current-controlled resistor at radio frequencies, so a bias current switches or attenuates a signal without the distortion an ordinary diode would cause. References, tuning and light emission belong to the Zener, the varactor and the light emitting diode respectively. Adding an undoped layer to change a device's high-frequency behaviour completely is a good illustration of how much structure matters alongside material.