This is a design of a half-wave rectifier that is uses only half of the input cycle to produce an output. The induced voltage across L2 (the transformer secondary) that will be shown on the schematic diagram. The dots (polarity marks) on the transformer indicate points of the same polarity. During the portion of the input cycle that is going positive (solid line), CR1, the PN junction diode, will be forward-biased and current will flow through the circuit. L2, acting as the source voltage, will have current flowing from the top to the bottom. This current then flows up through RL causing a voltage drop across RL equal to the value of current flowing times the value of RL. This voltage drop will be positive at the top of RL, with respect to its other side; and the output will therefore be a positive voltage with respect to ground. This is the figure of the schematic.
It is common practice for the end of a
resistor receiving current to be given a sign representing a negative polarity
of voltage, and the end of the resistor through which current leaves to be
assigned a positive polarity of voltage. The voltage drop across RL, plus the
voltage drop across the conducting diode will equal the applied voltage.
Although the output voltage will nearly equal the peak applied voltage, it
cannot reach this value due to the voltage drop, no matter how small, across
CR1. In a half-wave rectifier circuit the average DC output voltage is 0.318 of
the peak value of one half AC cycle.
The broken line illustrates the
negative half-cycle of the input. When the negative half-cycle is felt on CR1,
the PN junction diode is reverse-biased. The reverse current will be very
small, but it will exist. The voltage resulting from the reverse current, as
shown below the line in the output is exaggerated to bring out the point of its
existence. Although only one cycle of input is shown in schematic, it should be realized that
the action described above continually repeats itself, so long as there is an
AC input. By reversing the diode connection in the schematic, having the anode on the right instead of the left,
the output would now become a negative voltage. The current would be going from
the top of RL toward the bottom, making the output at the top of RL negative
with respect to the bottom or ground side.
