compre: diodes&apps

• Bias voltage connections: positive to anode (A), negative to cathode (K)
• Bias voltage must be greater than the barrier potential for forward bias
• Barrier potential is 0.7V for silicon diodes
• Majority carriers provide the forward current in a diode
• Forward bias narrows the depletion region
• Reverse bias connections: positive to cathode (K), negative to anode (A)
• Bias voltage must be less than the breakdown voltage for reverse bias
• Minority carriers provide a negligibly small reverse current
• Reverse bias widens the depletion region
• Forward bias: positive bias to anode (A) and negative bias to cathode (K), permits majority-carrier current
• Barrier potential for silicon diodes: 0.7V
• Majority carriers provide forward current
• Reverse bias: positive bias to cathode (K) and negative bias to anode (A), prevents majority-carrier current
• Bias voltage must be lower than the breakdown voltage for reverse bias
• No majority carrier current after the transition time
• The depletion region widens under reverse bias
• Full-wave rectifiers are commonly used in dc power supplies
• Two types of full-wave rectifiers: center-tapped and bridge
• Full-wave rectifiers allow unidirectional current flow through the load during the entire input cycle
• Output voltage frequency is twice the input frequency for full-wave rectification
• Output voltage pulsates every half-cycle of the input
• Frequency of output voltage: 2 times the input frequency
• A center-tapped rectifier uses two diodes connected to the secondary of a center-tapped transformer
• The input voltage is coupled through the transformer to the center-tapped secondary
• Half of the total secondary voltage appears between the center tap and each end of the secondary winding
• The center-tapped full-wave rectifier allows current flow through the load during both positive and negative half-cycles of the input waveform
• The output voltage of the center-tapped full-wave rectifier has a frequency twice that of the input frequency
• The average value is approximately 63.7% of the peak value for a full-wave rectified voltage
• Capacitor-input filter in power supplies provides a dc output approximately equal to the peak of its rectified input voltage
• Ripple voltage caused by the charging and discharging of the filter capacitor
• Smaller ripple voltage indicates a better filter
• Regulation of output voltage over a range of input voltages is called input or line regulation
• Regulation of output voltage over a range of load currents is called load regulation
• Diode limiters or clippers cut off or remove parts of a waveform above and/or below a specified level
• Diode clampers add a dc level to an ac voltage using a diode and a capacitor
• Three diode models: ideal diode, constant-voltage-drop model, piecewise-linear model.
• Choke-input filter provides a more filtered output by using a choke coil to limit the rate of change of current.
• Shunt capacitor filter reduces the ripple voltage by providing an additional low-impedance path for AC current.
• Capacitor-input filter reduces ripple voltage by storing energy during periods of high rectifier output and releasing it during periods of low rectifier output.
• Emitter follower configuration of a transistor can be used to provide voltage regulation.