DIODES AND APPLICATIONS CHAPTER 17 DIODES AND APPLICATIONS

Typical Diode package

Diode symbol

Diode Approximations The ideal diode model

การป้อนไฟให้ Diode Forward bias: ให้ศักย์ไฟฟ้าด้าน Anode ( P ) สูงกว่า Cathode ( N ) VF > VB (VB (Si ) = 0.7 V; VB (Ge ) = 0.3 V ) ป้อนไฟให้กระแสไหลในทิศตามลูกศร ของสัญลักษณ์ไดโอด Diode จะทำตัวเหมือน switch ปิด ยอมให้กระแสผ่านได้

Diode Approximations The complex diode model

DIODE CHARACTERISTICS Diode Characteristic Curve Reverse bias As the voltage (VR) increases to the left, the current remains near zero until the breakdown voltage (VBR) is reached When breakdown occurs, there is a large reverse current that can destroy the diode

การป้อนไฟให้ Diode Reverse bias: ให้ศักย์ไฟฟ้าด้าน Anode ( P ) ต่ำกว่า Kathode ( N ) ป้อนไฟให้กระแสไหลในทิศย้อนลูกศร ของสัญลักษณ์ไดโอด Diode จะทำตัวเหมือน switch เปิด ทำให้กระแสผ่านไม่ได้

Breakdown Voltage (VBR) Reverse bias สูงมาก จนกระทั่ง Depletion region ขยายจนเต็มพื้นที่ N และ P Avalanche Effect Free e- ฝั่ง P มีพลังงานสูงมากจนกระทั่ง ชน valence e- ใน P กลายเป็น Free e- ทำให้จำนวน Free e- เกิดเป็นจำนวนเท่าทวีคูณ ( rapid multiplication ) ทำให้เกิด Free e- ในฝั่ง P จำนวนมาก ไหลผ่านรอยต่อได้ กลายเป็นกระแสไหลในทิศย้อนกลับ

Diode Testing Working diode Open diode Shorted diode Forward bias: Voltmeter: 0.7 v Reverse bias: Voltmeter: 2.5 – 3.5 v (internal meter voltage) Open diode Forward & Reverse bias Voltmeter: 2.5-3.5 v Ohm meter: High resistance Shorted diode Voltmenter: 0 v Ohm meter: Low resistance

การใช้งาน diode กำหนดทิศการไหลของกระแสในวงจร วงจร rectifier ใน DC Power Supply กระแสสลับ (AC) 2 ขั้ว (+/-) ให้เป็น กระแสตรง ( DC) (ขั้วเดียว) วงจร Diode Limiter (จำกัดความต่างศักย์ ของสัญญาณ AC) วงจร Diode Clamper (ยกระดับความต่างศักย์ของสัญญาณ AC)

Basic DC power supply The dc power supply converts the standard 220 V,50 Hz into a constant dc voltage They consist of three parts : Rectifier, Filter, and Regulator The dc voltage produced by a power supply is used to power all types of electronic circuits, such as television receivers, stereo systems, VCRs, CD player

Power supply Figure 17-1

The Half-Wave Rectifier Average Value of the Half-wave output voltage VAVG=Vp (out) /  Figure 17-2

Effect of Diode Barrier Potential on Half-Wave Rectifier Output Voltage During the positive half-cycle, the input voltage must overcome the barrier potential before the diode becomes forward-biased Vp (out) =Vp (in) - 0.7 V Figure 17-5

Peak Inverse Voltage (PIV) The maximum value of reverse voltage, sometimes designated as PIV, occurs at the peak of each negative alternation of the input cycle when the diode is reverse-biased Figure 17-7

Average Value of the Full-wave rectified output voltage FULL-WAVE RECTIFIERS The full-wave rectifier is the most commonly used type in dc power supplies allowing unidirectional current to the load during the entire input cycle differ from the half-wave rectifier that allows only during one-half of the cycle Figure 17-9 Average Value of the Full-wave rectified output voltage VAVG= 2Vp (out) / 

Center-Tapped Full-Wave Rectifier Using two diode connected to the secondary of a center-tapped transformer At the positive half-cycle Forward-biases the upper diode D1 Reverse-biases the upper diode D2 At the negative half-cycle Reverse-biases the upper diode D1 Forward-biases the upper diode D2

Center-Tapped Full-Wave Rectifier

Effect of the Turn Ratio on Full-Wave Output Rectifier If the turn ratio of the transformer is 1:1, the output of the rectifier is equal to ½ of the input voltage Vp Owing to the voltage input is approximately equal to the output voltage, we must use the step-up transformer

Peak Inverse Voltage (full-wave rectifier)

Full-Wave Bridge Rectifier

Bridge Output Voltage

POWER SUPPLY FILTER AND REGULATORS After passed the rectifier, the output of the power supply is filtered for reduce the ripple, on the other hand, for make an output smoothly Capacitor-Input filter Ripple Voltage The voltage which change due to charging and discharge of the capacitor is called “ripple voltage”

Ripple Voltages for half-wave and full-wave

Ripple Factor (r) Ripple factor is the ratio of the Vr to VDC, expressed as : NOTE: the frequency in the full-wave rectifier is twice of the half-wave rectifier

Surge Current in the Capacitor-Input Filter

IC Regulators An integrated circuit regulator is a device that is connected to the output of a filtered rectifier and maintains a constant output voltage The capacitor-input filter reduces the input ripple to the regulator to an acceptable level and it is combined in IC regulator. The most IC regulators have three terminal Input terminal Output terminal Reference terminal

IC Regulators

Basic regulated power supply

Percent Regulation Line regulation Load regulation ∆VOUT Specifies how much change occurs in the output voltage for a given change in the input voltage Load regulation Specifies how much change occurs in the output voltage over a certain range of load current value ∆VOUT Line regulation = ∆VIN VNL- VFL Load regulation = VFL

Diode Limiter Diode Limiters Diode limiters (clipper) cut off above or below specified levels

Diode Limiting and Clamping Circuits Diode Limiters Adjustment of the limiting level

Diode Clampers Diode clamper known as a dc restorer Add a dc level to an ac signal

Diode Clampers

ชนิดของ Diode Regular diode Zener diode Varactor diode Light-Emitting diode (LED) Photo diode

ZENER DIODES symbol The zener diode is a silicon pn junction device and operate in the reverse breakdown region

Zener Breakdown (Vz) Two types of reverse breakdown in a diode Avalanche also occurs in the rectifier diode (regular diode) Zener Occurs in a zener diode at low reverse voltages NOTE : Zeners with breakdown voltage of 1.8 to 200 V are commercially available

Breakdown Characteristic Regulator: ตัวคงค่าความต่างศักย์

Zener Equivalent Circuit Regulator: ตัวคงค่าความต่างศักย์

Zener diode impedance The ratio of ∆Vz to ∆Iz is the zener diode impedance Normally, ZZ is specified at IZT ZZ is approximately constant over the full range of reverse-current values ∆VZ Zz = ∆IZ

Zener Voltage Regulation Zener diodes can be used for voltage regulation in noncritical low-current applications

Zener Voltage Regulation As the input voltage varies, the zener diode hole the constant voltage across the output terminals

Zener Regulation with a Varying Load The zener diode maintains a constant voltage across RL as long as the zener current is greater than IZK and less than IZM, this process is called load regulation

VARACTOR DIODES A varactor is basically a reverse-biased pn junction that utilizes the inherent capacitance of the depletion region The depletion region acts as a capacitor dielectric

VARACTOR DIODES

VARACTOR DIODES

VARACTOR DIODE APPLICATIONS

LEDs and PHOTODIODES There are two types of optoelectronic devices The Light Emitting Diode (LED) The photodiode (light detector)

The Light Emitting Diode (LED) When the device is forward-biased, electrons across the pn junction from the n-type material and recombine with the holes in the p-type material When recombination takes place, the recombining electrons release energy in the form of heat and light

The Light Emitting Diode (LED) The semiconductive materials used in LEDs are gallium arsenide(GaAs), galium arsenide phosphide (GaAsP), and Gallium phosphide (GaP) Silicon and Germanium are not used because they are very poor at producing light GaAs LEDs emit infrared (IR) radiation GaAsP produces either red or yellow visible light GaP emits red or green visible light

The Light Emitting Diode (LED) symbol electroluminescence

The Light Emitting Diode (LED)

The Light Emitting Diode (LED) Applications

The Photodiode The photodiode is a pn junction device that operates in reverse bias

The Photodiode

The Photodiode operation

The Photodiode Applications

The diode data sheet

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