Rectifiers

• Rectifiers convert alternating current into direct current and find use in power supplies for this purpose. Three types of rectifiers include the half-wave, full-wave and bridge. All convert alternating current into a pulsating current that only flows in one direction.
  
  Half-wave rectifiers use a single diode and only use half of the alternating current cycle. Full-wave rectifiers use two diodes, and bridge rectifiers use four. Full-wave and bridge rectifiers use the full alternating current cycle.
  
  Filter circuits further modify the output of a rectifier circuit into a cleaner, non-pulsating, direct current.
  
  

Clamping Circuits

• Clamping circuits prevents a voltage from falling below a certain level. These circuits take advantage of the diode's forward voltage drop, the amount of voltage necessary to make a diode conduct. By connecting multiple diodes in series, the output of one feeds the input of the next, the forward voltage drop of each diode adds to the clamping level.
  
  The diodes connected in series are treated as a single device which is connected in parallel. This means the input of the first diode is also connected to the input of the load, and the output of the last diode is connected to the load output -- with the load.
  
  Since voltage in a parallel circuit is constant, the voltage drop across the load will never fall lower than the total forward voltage drop across the diodes.
  
  

Binary Logic Circuits

• Diode logic circuits are no longer common, but they were used in early computers. In a logic circuit, the absence or near absence of voltage indicates a low state. A high state is indicated by the presence of a voltage, usually about 5 volts. Some variance is allowed.
  
  One example of a logic circuit is the "Or" circuit. An "Or" circuit tests whether either or both of two inputs has a high state. If input "A" is high, the circuit outputs a high. The same is true for input "B," or if both "A" and "B" are high. If both "A" and "B" are low, the circuit outputs a low state.
  
  

Voltage Multipliers

• Voltage multipliers combine two diode circuits:: a half wave rectifier and a DC restorer circuit. The restorer circuit is a simple voltage clamp used in conjunction with a capacitor. When the two circuits are combined, the alternating current output is twice the input voltage. For example, 120 volts doubles to become 240 volts.
  
  The simple combination of a one half-wave rectifier and a DC restorer circuit is called a voltage doubler. You can cascade these circuits -- the output of one is the input of the next -- to produce very high voltages. A cascade of 20 voltage doubler circuits can raise 120 volts to nearly 5,000 volts.
  
  

Radio Signal Receivers

• The simplest of radio receivers uses a diode to rectify the received radio waves into a pulsating direct current signal. This circuit uses a coil and a capacitor connected to an antenna. You can adjust the coil to select the number of turns of wire used, which is how to select the frequency of the received signal.
  
  The selected signal is passed on to the diode, which rectifies it into a pulsating direct current. The pulsating current goes directly to a speaker, headphone or earphone, where it is converted into sound.
  
  In the late nineteenth and early twentieth centuries, this type of radio receiver used a crystal with a fine wire to rectify the signal and was called a crystal radio.