lab7_u11_diodes

# lab7_u11_diodes - University of Florida Department of...

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University of Florida EEL 3111 — Summer 2011 Drs. E. M. Schwartz & R. Srivastava Ode Ojowu, TA Page 1/7 Revision 0 7-Jul-111 Lab 7: Diode Circuits OBJECTIVES To reinforce the concepts behind diode circuit analysis Verification of diode theory and operation To understand certain diode applications, such as rectification and clipping MATERIALS Your lab parts. Printouts (required) of the below documents: o Pre-lab analyses o Answers to pre-lab questions o Multisim screenshots e-mailed to course e-mail Graph paper. INTRODUCTION Device Theory and Operation A solid state diode consists of a junction of either dissimilar semiconductors ( pn junction diode) or a metal and a semiconductor (Schottky barrier diode). Regardless of the type, the circuit symbol for a diode is as shown in Fig. 1 (left) and the corresponding device in Fig. 1 (right). If V is positive, the diode is forward-biased and the diode can conduct a significant positive current I , even though V is a small voltage (typically 0.7 V0 for the most common [silicon] diodes). If V is negative, the diode is reverse-biased ; the negative current produced by the reverse bias is so small that it is often considered to be zero. Thus, the usual function of a diode is to allow current to flow in the direction of the arrow (the forward direction) for positive V’ s, but not allow any current to flow in the reverse direction for negative V’ s. Only a small forward bias (positive V ) is required to cause a diode to conduct a significant current I , and the less this voltage, the better. One model of an ideally diode has the following properties: This voltage drop for forward bias is zero volts. The diode can conduct any value of current I in the forward direction, with this value being determined not by the diode, but by other components in the circuit in which the diode is connected. The diode conducts zero amperes for a negative V , regardless of the voltage magnitude. In other words, an ideal diode is a short circuit for a voltage V that tends to be positive (but it cannot be more than 0 V) and an ideal diode is an open circuit for a negative V . Thus, an ideal diode acts like a switch that is closed for current flow in the direction of the arrow in the diode circuit symbol, and open otherwise. Essentially, it is an electronically operated switch. This ideal approximation is satisfactory for analyzing many circuits that contain diodes, provided that the voltage levels are much greater than 0.7 V. Fig. 2 shows the I-V (current/voltage) characteristic for an ideal diode. Figure 1 – Diode schematic symbol (left) and physical representation (right)

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University of Florida EEL 3111 — Summer 2011 Drs. E. M. Schwartz & R. Srivastava Ode Ojowu, TA Page 2/7 Revision 0 7-Jul-111 Lab 7: Diode Circuits Figure 4 – Circuit to obtain an I-V characteristics via oscilloscope display. Fig. 3 shows the
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lab7_u11_diodes - University of Florida Department of...

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