Alternating Current Source

0 1ALTERNATING CURRENT SOURCE One of the less known properties of field effect transistors is that some of these are electrically symmetrical, which means that the drain and source may be interchanged under certain con- ditions. This circuit is based on this phenonemenon, and feeds a constant alternating current through P2 when connected to an alternating voltage source. The operation is best explained with reference to the curves of Fig. 2, and by assuming that a sinusoidal voltage is ap- plied to terminals A and B. When the drain of Ti is negative with respect to the source, Di blocks, and forms a resistance that is considerably higher than that of RI. This has virtually no voltage on it, so that Vcs= 0 V. This means that ID is constant at about 19 mA when VDs>8 V (see Fig. 2a). It should be noted that the curves and values of ID and VDS are typical, and may deviate depending on the FET used (A, B or C suffix). When the drain of Ti is positive with respect to the source, Di cond...