The output characteristics of switched-mode dc-dc buck power converter are discussed. The shape of output characteristics is especially important for converters used for supplying modern processors. An output impedance is usually used for description of output characteristics. Many efforts are described in the literature to obtain the satisfastory features of closed-loop output impedance. Another approach, presented in the paper, is based on the concept of the output voltage response corresponding to the load conductance change, and is expressed by hr transmittance. Simulations of output characteristics of the buck converter in frequency and in time-domain have been performed for the ideal case as well as for a more realistic situation, with the parasitic resistances of converter elements included. The measurement results differ substantially from characteristics calculated for an ideal converter and are in good consistency with simulations including parasitics.
 R.W. Erickson and D. Maksimovic, Fundamentals of PowerElectronics, 2-nd Ed., Kluwer, Berlin, 2002.
 M.K. Kazimierczuk, Pulse-Width Modulated DC - DC PowerConverters, J. Wiley, London, 2008.
 W. Janke, “Averaged models of pulse-modulated DC-DC converters. Part I. Discussion of standard methods”, Archives ofElectrical Engineering 61 (4), 609-632 (2012).
 Voltage Regulator Module (VRM) and Enterprise Voltage Regulator-Down (EVRD), 11.1 Design Guidelines, Intel Corp., 2009.
 R.P. Singh and A.M. Khambadkone, “A Buck-derived topology with improved step-down transient response”, IEEE Trans.on Power Electronics 23 (6), 2855-2866 (2008).
 K. Yao, M. Xu, Y. Meng, and F.C. Lee, “Design considerations for VRM transient response based on the output imedance”, IEEE Trans. on Power Electronics 18 (6), 1270-1277 (2003).
 D. Chen, F.C. Lee, and S.J. Chen, “Evaluation of various Adaptive Voltage Positioning (AVP) schemes for computer power sources”, J. Chinese Institution of Engineers 30 (7), 1137-1143 (2007).
 M. Lee, D.C. Huang, K. Chih-Wen, and L. Ben Tai, “Modeling and design for a novel adaptive voltage positioning (AVP) scheme for multiphase VRM”, IEEE Trans. on Power Electronics 23 (4), 1733-1742 (2008).
 S. Xiao, W. Qiu, G. Miller, T.X. Wu, and I. Batarseh, “Adaptive modulation control for multiple-phase voltage regulators”, IEEE Trans. on Power Electronics 23 (1), 495-499 (2008).
 R. Ahmadi, D. Paschedag, and M. Ferdowsi, “Closed loop input and output impedances of DC-DC switching converters operating in voltage and current mode control”, IECON 36-thAnnual Conf. IEEE Industrial Electronic Society 1, 2311-2316 (2010).
 C.W. Liu, “Load transient response of a DC/DC converter in GSM/Edge handset applications”, High Frequency Electronics 1, 18-26 (2007).
 W. Wojtasiak, “The electrothermal modeling of high power microwave FET and its applications”, Electronic and Telecom. Quarterly 51, 85-104 (2005).
 J.A. Qahouq and V.P. Arikatla, “Power converter with digital sensorless adaptive voltage positioning control scheme”, IEEETrans. on Industrial Electronics 58 (9), 4105-4116 (2011).
 “Line and load transient testing for power supplies”, MaximAppl. Note 3443.
 J. Williams, “Load transient response testing for voltage regulators”, Linear Technology Appl. Note 104, CD-ROM (2006).
 J.T. Mossoba and P.T. Krein, “Output impedance of high performance current mode DC-DC Buck converters, with application to voltage-regulator module control combinations”, APEC’04 19-th Annual IEEE Conf. 2, 1315-1321 (2004).
 V. ˇSvikoviˇc, J. A. Oliver, P. Alou, O. Garcia, and J.A. Cobos, “Synchronous Buck converter with output impedance correction circuit”, APEC 2012, 27-th Annual Conf. 1, 727-734 (2012).
 S.K. Mishra, “Design-oriented analysis of modern active droop-controlled power supplies”, IEEE Trans. on IndustrialElectronics 56 (9), 3704-3708 (2009).
 W. Janke, M. Walczak, and M. Bączek, “Input and output characteristics of Buck and Boost converters including parasitic resistances”, Electrical Review 11 B, 2012, to be published, (in Polish).
 W. Janke, “Averaged models of pulse-modulated DC-DC converters. Part II. Models based on the separation of variables”, Archives of Electrical Engineering 61 (4), 633-654 (2012).
 W. Janke, “The extension of small signal model of switching dc-dc power converters”, XII Symp. PPEEm’2007 2, 241-246 (2007).