9. REVERSE RECOVERY TIME: Ministry of teaching& high education Al- Mustansiriya University College of engineering Computer & Software engineering     1' class Electronic 1 9. REVERSE RECOVERY TIME: Reverse recovery time, denoted by trr . If the applied voltage should be reversed to establish a reverse-bias situation, we would ideally like to see the diode change instantaneously from the conduction state to the nonconduction state. Diode current will simply reverse as shown in Fig. 1.29 and stay at this measurable level for the period of time ts (storage time) required for the minority carriers to return to their majority-carrier state in the opposite material. The current will reduce in level to that associated with the nonconduction state. This second period of time is denoted by tt (transition interval). This is an important consideration in high – speed switching applications. Most commercially available switching diodes have a trr in the range of afew nanoseconds to 1µs (Schottky diode). Figure 1.29 Defining the reverse recovery time. Schottky diode

11. LED & OTHER TYPES OF DIODES 10. ZENER DIODES Zener diodes are available having Zener potentials of 1.8 to 200 V with power ratings from ¼ to 50 W. There is a slight slope to thegharacteristics requiring the piecewise equivalent model appearing in Fig.(1-20) for zener region, while it is assumed as ideal with a straght vertical line at the zener potential. Fig. 1.20 Zener- diode test Characteristics with the equivalent model for each region 11. LED & OTHER TYPES OF DIODES Figure 1.54 (a) Process of electroluminescence in the LED; (b) graphic symbol

+ - LED Photo Diode - Photo Diode LED Optical Isolator

Diode Applications CHAPTER TWO 2.1 Introduction. 2.2 Load – Line Analysis. 2.3 Series Diode Configurations. 2.4 Parallel & Series – Parallel Configurations. 2.5 AND / OR Gates. 2.6 Sinusoidal Input: Half – Wave Rectifier. 2.7 Full – Wave Rectification. 2.8 Clippers. 2.9 Clampers. 2.10 Zener Diodes. 2.11 Voltage – Multiplier Circuits. 2.12 Power Supply. 2,12.1 Introduction. 2.12.2 General Filter Considerations. 2.12.3 Capacitor Filter. 2.12.4 RC Filter.

2.1 INTRODUCTION The construction, characteristics, and models of semiconductor diodes were introducedin Chapter 1. This chapter demonstrates an interesting and very useful a spect of the study of a field such us electronic devices and systems. once the basic behavior of a device is understood, its function and response in an infinite variety of configurations can be determined. The analysis will proceed from one that employs the actual diode characteristic to one that utilizes the approximate models almost exclusively. This is usually accomplished through the approximation process, which can develop into an art itself. The variation may be slight, but it will often be sufficient to validate the approximations employed in the analysis. All these tolerances contribute to the general belief that a response determined through an appropriate set of approximations can often be “as accurate” as one that employs the full characteristics. The use ofappropriate approximations, thereby avoiding an unnecessary level of mathematical complexity.

2.2 LOAD-LINE ANALYSIS Consider the network of Fig. 2.1a employing a diode having the characteristics of Fig. 2.1b. Note in Fig. 2.1a that the “pressure” established by the battery is to establish a current through the series circuit in the clockwise direction. The fact that this current and the defined direction of conduction of the diode are a “match” reveals that the diode is in the “on” state and conduction has been established. The resulting polarity across the diode will be as shown and the first quadrant (VD and ID positive) of Fig. 2.1b will be the region of interest—the forward-bias region. Figure 2.1 Series diode configuration: (a) circuit; (b) characteristics

Applying Kirchhoff’s voltage law to the series circuit of Fig. 2 Applying Kirchhoff’s voltage law to the series circuit of Fig. 2.1a will result in: OR The two variables of Eq. (2.1) (VD and ID) are the same as the diode axis variables of Fig. 2.1b. This similarity permits a plotting of Eq. (2.1) on the same characteristics of Fig. 2.1b. The intersections of the load line on the characteristics can easily be determined if one simply employs the fact that anywhere on the horizontal axis ID = 0 A and anywhere on the vertical axis VD = 0 V. And As shown in Fig. 2.2. If we set ID = 0 A in Eq. (2.1) and solve for VD, we have the magnitude of VD on the horizontal axis. Therefore, with ID = 0 A, Eq. (2.1) becom And

Figure 2.2 Drawing the load line and finding the point of operation. We now have a load line defined by the network and a characteristic curve definedby the device. The point of intersection between the two is the point of operation for this circuit.

2.3 SERIES DIODE CONFIGURATIONS Where VT = VK = 0.7 V for Si

The forward resistance of the diode is usually so small compared to the other series elements of the network that it can be ignored. Using approximate equivalents for a silicon diode and an ideal diode that appear in table 2.1 . In general, a diode is in the “on” state if the current established by the applied sources is such that its direction matches that of the arrow in the diode symbol, and VD ≥ 0.7V for silicon, VD ≥ 0.3V for germanium. And VD ≥ 1.2V for Gallium Arsenide. The primary purpose of this book is to develop a general knowledge of the behavior, capabilities, and possible areas of application of a device in a manner that will minimize the need for extensive mathematical developments. Figure 2.3 Determining the state of the diode of Fig. 2.10. Figure 2.12 Substituting the equivalent model for the “on” diode of Fig. 2.10. The series circuit of Fig.(2.3). Since E ˃ Vk, the diode is in the “on” state, the network is then redrawn as in Fig.(2.4)

For reverse bias diode

2.4 PARALLEL AND SERIES–PARALLEL CONFIGURATIONS The methods applied in Section 2.4 can be extended to the analysis of parallel and series–parallel configurations. For each area of application, simply match the sequential series of steps applied to series diode configurations. EXAMPLE 2.6: Determine the current I1, I2 and ID2 for given network? Solution: Figure 2.6 Network for Example Figure 2.7 Determining the unknown quantities for the network of Example 2.12

EXAMPLE 2.7 Determine the currents I1, I2, and ID2 for the network of Fig. 2.7?