Rectifier and Smoothing Circuit

A rectifier is a circuit that performs AC to DC conversion. AC, an acronym for Alternating Current, means sinusoidal variation with time. DC, an acronym for Direct Current, means constant. Hence, a rectifier converts a sinusoidal voltage to a constant voltage. Most rectifiers utilize one or more semiconductor diodes. The theory behind diode operation will be investigated in the next lab exercise. For now, think of a diode as a one-way valve. While re-examining Figure , consider what happens in the receiver circuitry. The two coils are linked via mutual inductance. Since the transmitter input will be connected to the function generator and driven with an AC (sinusoidal) voltage, the current through the transmitting coil will be sinusoidal. Therefore, the induced voltage across the receiving coil will be sinusoidal as well. In order to drive the servo controller, we need a DC voltage. Hence, we will use a rectifier circuit to perform this conversion. The rectifier (and smoothing circuit) is composed of , and in Figure . The induced sinusoidal voltage across the receiving coil will cause a current to flow to the right through Diode 2, but only during the positive half-cycle of the induced voltage. During the negative half-cycle, the induced voltage across the receiving coil attempts to force current to the left through Diode 2. However, due to the unidirectional one-way valve nature of the diode, no current flows through it. The capacitor charges during the positive half-cycle and discharges through resistor during the negative half-cycle. However, since the time constant is s (see item 1 below) which is large compared to the period of the sinusoidally induced voltage, the next positive half-cycle occurs before the capacitor discharges at all. The result is a nearly constant (DC) voltage across and . As will be seen in the next lab, the DC voltage across and will depend on the amplitude of the current through the transmitting coil.

1. Obtain a germanium diode (labeled ``Germanium Diodes" in one of the EE-61 parts bins), a 4.7 nF mylar capacitor , and a 10 M resistor .
2. Assemble the transmitter and receiver circuits, but do not
   a) make the connection between the rectifier and the non-inverting amplifier.
   b) connect the potentiometer. There are not enough potentiometers for every pair of lab partners. Therefore, when you test your circuits next week, you will use a potentiometer and then return it to the parts bin.

Return any unused parts to the correct drawer in the parts bin. In the next lab you will perform test measurements of the transmitter and receiver circuits.