Laboratory 6: Transformers - Circuit Analysis II Laboratory | EE 304, Lab Reports of Microelectronic Circuits

Download Laboratory 6: Transformers - Circuit Analysis II Laboratory | EE 304 and more Lab Reports Microelectronic Circuits in PDF only on Docsity! Name: ___________________________ Lab Instructor: _________________ Date Performed: ________________ Date Due: _______________________ Lab Partner(s): ______________________________________________________ © 2008 Simon J. Tritschler. All Rights Reserved. EE 304 Laboratory VI Transformers Transformers can be very useful devices. They can manipulate AC signals such that voltage can be stepped up or down, with current changed in the opposite proportion. They can couple AC signals while blocking DC components. They can isolate signals in situations where they might not be referenced to the same potential. Transformers can even accomplish the task of polarity inversion in applications where two signals equal in magnitude but opposite in phase might be needed, and any combination of these features can often be realized with a single transformer if necessary. However, despite these valuable attributes, transformers have performance limitations which can be serious if not taken into consideration when choosing and using them. In this laboratory, we investigate a practical transformer and its characteristics. Frequency Response In an ideal transformer, any AC voltage at any frequency applied to the primary winding will be coupled to the secondary winding in proportion to the turns ratio, N1:N2 (and vice versa). Consequently, the ideal transformer, being perfectly efficient, will have a current transfer of N2:N1 and the impedance ratio will be (N1:N2)². However, probably the single most important specification for a transformer, besides its turns ratio, is its frequency response, which is always limited by several factors. Of these, the main two are primary inductance and leakage inductance. An ideal transformer will accomplish its voltage or impedance transfer without contributing any loading of its own, implying perfect mutual coupling between infinite inductances, thus allowing no self-current in the magnetic circuit; however, this is impossible in practice and the inductance of the primary winding, in conjunction with the source resistance of the generator, creates a high-pass filter which inhibits low frequency response. On the other hand, leakage flux is inevitable due to imperfect magnetic coupling and appears as an inductance in series with the primary circuit; thus, in conjunction with the reflected secondary impedance, forms a low-pass filter which compromises high-frequency response. © 2008 Simon J. Tritschler. All Rights Reserved. Consider a 2:1 transformer with a center-tapped secondary winding. The transformer specified (P/N 3464575-3, manufacturer unknown) is to be used in a circuit driving a 600-Ω balanced line, fed from a signal source having a 2.4-kΩ source resistance. Refer to the circuit, ignoring the secondary winding’s center tap for this application: N1 N2 + 1. Build the circuit. Compensate for the output resistance of the signal generator by reducing RS if necessary. Use two 300-Ω resistors in series for RL. Feed a 2-VPK-PK signal into the circuit at 1 kHz and measure the secondary voltage using your oscilloscope. Be sure to measure the primary winding voltage at the transformer connection, not the generator. Use this information to find the turns and impedance ratios. VPRI. = __________ VPK-PK VSEC. = __________ VPK-PK N1:N2 = VPRI. / VSEC. : 1 = __________ : 1 Z1:Z2 = (VPRI. /VSEC.)² : 1 = __________ : 1 Now measure the frequency response of the transformer in-circuit. Find the two −3-dB points and record these cutoff frequencies. fL = __________ Hz fH = __________ kHz + VOUT − RS = 2.4 kΩ VSOURCE 2 VPK-PK SINE RL = 600 Ω BLK RED BLU BLU/WHT