Electronic Circuits. Special-Purpose Diodes. Dr. Manar Mohaisen Office: F208 Department of EECE

Transcription

1 Electronic Circuits Special-Purpose Diodes Dr. Manar Mohaisen Office: F208 Department of EECE

2 Class Objectives Explain the Operation of the ener Diode Explain Applications of the ener Diode Explain the Operation and Applications of the Varactor Diode Explain the Operation and Applications of the Optical Diodes Other Types of Diodes Discussions

3 The ener Diode I F ener Diode It is named after Clarence Melvin ener. Breakdown V R V V F Characteristics Works in the reverse breakdown region. Reversebreakdown region I R In the operation region, the voltage is almost constant even though the current changes drastically. Two types of breakdowns: Avalanche breakdown: Occurs at high reverse voltages (> 5V). ener breakdown: Occurs at low reverse voltages ( ~ 5V ). Cathode (K) Anode (A) ener diode symbol C. ener (1905 ~ 1993)

4 The ener Diode contd. Breakdown Characteristics For currents less than I K, as V R increases, negligible change occurs in the current. Breakdowns starts at a reverse current of I K. The internal resistance of the ener diode decreases. Current increases drastically but voltage remains almost constant. To keep the ener diode in the breakdown region ] I K, I M [. Avoid working near the boundaries, i.e., close to I K or I M. ener diode acts as a regulator? YES! ener nominal voltage Preferable range of current to maintain the ener diode in the breakdown region.

5 The ener Diode contd. ener Models Ideal Model The ener diode is represented as a DC voltage. The value of the DC voltage is V. ener doesn't produce voltage but it is modeled as a DC voltage. ener diode s resistance and reverse current are neglected.

6 The ener Diode contd. ener Models contd. Practical Model The ener diode is represented as a DC voltage in series with a resistance. ΔV = Δ I

7 The ener Diode contd. ener Models contd. Example 3-1 ΔV = Δ I 50 mv = = 10 Ω 5mA

8 The ener Diode contd. Temperature Coefficient First Formula Δ V = V TC Δ T V : nominal ener voltage at a reference temperature of 25 o C TC : temperature coefficient (%/ o C) Positive value voltage increases with increase in temperature. Negative value voltage decreases with increase in temp. ΔT : change in temperature from the reference temperature Second Formula Δ V = TC ΔT With TC : temperature coefficient (mv / o C)

9 The ener Diode contd. Temperature Coefficient contd. Example 3-2 An 8.2 V ener diode (i.e., 8.2 V at 25 o C) TC equals 0.05%/ o C What is the ener voltage at 60 o C? Therefore, Δ V = V TC Δ T = = 144 mv (8.2V)(0.0005oC)(60oC 25oC) V = V +Δ V = 8.2V + 144mV = V at 60oC

10 The ener Diode contd. Power Dissipation and Derating Power Dissipation (loss) Power Derating The operation of reducing the rated maximum power according to a derating factor to prolong the device s life. Example P = V I D P = P Δ T (mw / o C) D(derated) D(max) Maximum power rating of 400 mw at 50 o C Derating factor of 3.2 mw/ o C. Determine the maximum power the ener can dissipate at 90 o C. P = (mw / o C) D(derated) Δ D(max) o o o = 400mW (3.2 mw / C)(90 C 50 C) = 400mW 128 mw = 272 mw

11 Class Objectives Explain the Operation of the ener Diode Explain Applications of the ener Diode Explain the Operation and Applications of the Varactor Diode Explain the Operation and Applications of the Optical Diodes Other Types of Diodes Discussions

12 ener Diode Applications Note ener diode is operating in the reverse breakdown region. I K < I < I M ener Regulation with a Varying Input Voltage V = 10 V, I K = 0.25 ma, P D(max) = 1W Ideal Model Maximum current I M PD(max) = = 1W = 0.1A V 10V Minimum input voltage V IN(min) = 0.25 ma * V = V Maximum input voltage V IN(max) = 0.1 A * V = 32 V Note on Example 3-5

13 ener Diode Applications contd. ener Regulation with a Variable Load I T is divided between I and I L Low load has higher current I is reduced. I must remain larger than I K to keep the diode regulating. High load has lower current I is increased. I must remain smaller than I M to keep the diode regulating.

14 Example 3-6 Determine the maximum and minimum load currents to keep the ener diode regulating. V = 12V, I K = 1mA, I M = 50 ma. ener Diode Applications contd. Solution The maximum ener current occurs when I L = 0 (R L = ) ener diode can handle this current because it is less than I M. The maximum load current happens at the minimum I = I K. IL(max) = IT IK = 25.5 ma 1mA = 24.5 ma I V V 24V 12V R 470Ω = IN = = (max) 25.5mA Therefore, V R 12V L = = = 490Ω I 24.5mA L(max)

15 ener Diode Applications contd. Three-terminal Voltage Regulator V IN Control element V OUT Ref Error amplifier Feedback element V IN Voltage regulator V OUT Reference ground

16 ener Diode Applications contd. ener Limiting

17 Example 3-8 Determine the output voltage ener Diode Applications contd. Solution

18 The Varactor Diode Varactor Diode It is a diode that always operates p n in reverse-bias. It is doped to maximize the inherit capacitance of the depletion region. Plate V BIAS + Plate Dielectric The depletion region acts as a capacitor because of its nonconductive characteristic. The capacitance is given by: C = Aε d A : Plate area ε : Dielectric constant d : Plate separation

19 The Varactor Diode contd. Varactor Diode Capacitance vs. reverse voltage. Capacitance Capacitance parameters are controlled by the method of doping and the diode construction.

20 The Varactor Diode contd. Applications It acts as a variable capacitor controlled by the reverse-bias voltage. Tuning applications (Resonant circuits) f r 1 2π LC In the Figure R 3 controls the bias voltage. As a result, the capacitance is modified, And the resonant frequency is modified.

21 The Light-Emitting Diode (LED) LED Free electrons (conduction band) move from the n-region to combine with the holes (valence band) in the p-region. When the recombination takes place, electrons release energy that is emitted as light. [Electroluminescence Process] The wavelength of the emitted light is controlled by adding impurities Light output (normalized) λ, wavelength (nm)

22 The Light-Emitting Diode (LED) contd. LED Radiation pattern is controlled using lens. The narrower the radiation pattern, the more the light is concentrated. Applications Indicator lamps Readout displays LEDs are used in the seven-segment display device.

23 Let s Express Ourselves in English! Group Activity [10.xx] High-Intensity LEDs [Group 1] The Organic LED (OLED) [Group 2] The Photodiode [Group 3] + Current Regulator Diode The Laser Diode [Group 4] The Schottky Diode [Group 5] + The Tunnel Diode The PIN Diode [Group 6] + Step-Recovery Diode

24 Discussion & Notes K K A K A A A A K K K K A K A K K A K A K A