ECE-03-PRELIM-LEC1.pdf

ECE 03 – ELECTRONICS 3: ELECTRONICS SYSTEM & DESIGN BSECE III GH BSECE III GG ENGR. JOEL ANTHONY L. SEVILLA SEPTEMBER 2023 Course Description This course involves the theory, operating characteristics and design of electronics devices and control cir...

ECE 03 – ELECTRONICS 3: ELECTRONICS SYSTEM & DESIGN BSECE III GH BSECE III GG ENGR. JOEL ANTHONY L. SEVILLA SEPTEMBER 2023 Course Description This course involves the theory, operating characteristics and design of electronics devices and control circuits for industrial processes; industrial control applications; electronic instrumentations; transducers; data acquisition system; interfacing techniques; sensors. Textbooks and references Electronic Devices and Circuit Theory, th Boylestad and Nashelsky, 12 ed, 2013 Electronic Devices, Floyd, 9th ed, 2012 Basic Electronics, Gupta, 2017 Grob’s Basic Electronics, Shultz, 12th ed, 2011 Textbooks and references A Textbook of Electronics Engineering, Sharma, 2017 Electronic Devices and Circuits, Gupta, 6th edition, 2012 Course Requirements Exams 40% Quizzes 30% Assignments/SW 15% Attendance/Recitation 15% Total 100% GRADING SYSTEM Passing weighted average of 60%. Course Outline 1. Introduction, SCRs, UJT, PUT 2. TRIAC, DIAC, and other Thyristors 3. Optoelectronic Devices and Sensors 4. Transducers 5. Interfacing Techniques 6. Programmable Logic Controllers Course Outline 7. Building Management Systems including HVAC Controls 8. Security and Surveillance Control System 9. Audio Video and Lighting Controls 10. Supervisory Controls and Data Acquisition 11. Fire and Life Safety Controls PNPN AND OTHER DEVICES THYRISTORS Thyristors refer to a class of solid state silicon switching devices made up of four layer PNPN structure. These devices are used to control large amount of current on industrial electrical equipment. Thyristors are switching devices that don’t require any control current once they are turned on. All they require to snap them on is a quick pulse of control current. When the pulse current stops thyristors keep going as though nothing happened. Thyristors originated from the words THYRatron and transISTOR. Like transistors, these devices have two terminals for working current and one terminal for control current. Unlike the transistors, thyristors don’t require any further control current once they are turned on. Consequently, the control circuitry is typically quite simple and consumes little power. A thyristor acts as an open circuit, capable of withstanding a certain voltage until they are triggered. When triggered, they turn on and become low- resistance current paths and remain so, even after the trigger is removed, until the current is reduced to a certain level. There are two kinds of thyristors: unidirectional and bidirectional. Unidirectional Thyristors Allows a unidirectional flow of currents, similar to an ordinary diode, conducts at forward bias condition only. Examples are SCR, and Shockley diode. Bidirectional Thyristors Allows the two direction of current flow to pass through. Examples are the Diacs and the Triacs.  3 States of Thyristors Reverse blocking mode — Voltage is applied in the direction that would be blocked by a diode. Forward blocking mode — Voltage is applied in the direction that would cause a diode to conduct, but the thyristor has not been triggered into conduction.  3 States of Thyristors Forward conducting mode — The thyristor has been triggered into conduction and will remain conducting until the forward current drops below a threshold value known as the "holding current".  Common types of Thyristors 1. Shockley Diode 2. Silicon Controlled Rectifier (SCR) 3. Light Activated Silicon Controlled Rectifier (LASCR) 4. Silicon Unilateral Switch (SUS) 5. Diode for AC (DIAC)  Common types of Thyristors 6. Triode for AC (TRIAC) 7. Silicon Controlled Switch (SCS) 8. Programmable Unijunction Transistor (PUT) UNIDIRECTIONAL THYRISTORS Silicon Controlled Rectifier (SCR) The SCR is a rectifier constructed of silicon material with a third terminal for control purposes. Silicon was chosen because of its high temperature and power capabilities. SCR have been designed to control powers as high as 10 MW with individual ratings as high as 200 Amperes at 1800 Volts. Its frequency range of application is extended to about 50 kHz. Introduced in 1956 by Bell Telephone Laboratories. The basic operation of the SCR is different from the fundamental two-layer semiconductor diode in that a third terminal called a gate, determines when the rectifier switches from the open circuit to the short circuit state. In the conduction region the dynamic resistance of the SCR is 0.01 to 0.1Ω. The reverse resistance is typically 100 kΩ or more. fig. SCR (a) schematic symbol (b) basic construction and (c) transistor equivalent SCR different packaging type In addition to gate triggering, SCRs can also be turned on by significantly raising the temperature of the device or raising the anode to cathode voltage to the break over value. An SCR cannot be turned off by simply removing the gate signal. Two methods for turning off an SCR are anode current interruption and the forced commutation technique. Applications for SCRs Relay controls, time delay circuits, regulated power supplies, static switches, motor controls, choppers, inverters, battery chargers, protective circuits, heater controls and phase controls. SCR Specifications Breakdown Voltage – is the voltage at which the blocking capability fails and a massive amount of current rushes through, SCR’s use the terms “absolute maximum forward blocking voltage” and “absolute maximum reverse blocking voltage”. SCR’s can stand 100 volts in either direction without breaking down. SCR Specifications Operating Speed – SCR is specified in terms of “turn on time” and “commutating turn off time”. The term commutating is included as a reminder that the device does not turn off by itself, but rather is turned off by an interruption of the power supply. Typical switching speeds are 1 and 2 microseconds. SCR Specifications Gate Triggering Current – specifies how much current is required to turn the device on. Typical example is no more than 100 mA is required. Gate Triggering Voltage – specifies the voltage required to trigger the device, which is no more than 0.7 volts. SCR Operation Turning the SCR on When gate current, 𝐼𝐺 , is zero, the device acts as a 4-layer diode in the off state. When a positive pulse of current (trigger) is applied to the gate, both transistors turn on. The device stays on (latches) once it is triggered on. Turning the SCR on an SCR can also be turned on without gate triggering by increasing the anode-to-cathode voltage to a value exceeding the forward- breakover voltage. The forward-breakover voltage decreases as 𝐼𝐺 is increased above 0 V. Turning the SCR off Anode Current Interruption – using either a momentary series or parallel switching arrangement Turning the SCR off Forced Commutation– requires momentarily forcing current through the SCR in the direction opposite to the forward conduction so that the net forward current is reduced below the holding value SCR Characteristics Forward-breakover voltage, 𝑉𝐵𝑅(𝐹) - voltage at which the SCR enters the forward-conduction region; 𝑉𝐵𝑅(𝐹) is maximum when 𝐼𝐺 = 0 and is designated 𝑉𝐵𝑅(𝐹0). SCR Characteristics Holding current, 𝐼𝐻 - anode current below which the SCR switches from the forward- conduction region to the forward-blocking region; value increases with decreasing values of 𝐼𝐺 and is maximum when 𝐼𝐺 = 0. SCR Characteristics Gate trigger current, 𝐼𝐺𝑇 - value of gate current necessary to switch the SCR from the forward- blocking region to the forward-conduction region under specified conditions SCR Characteristics Average forward current, 𝐼𝐹(𝑎𝑣𝑔) - maximum continuous anode current (dc) that the device can withstand in the conduction state under specified conditions SCR Characteristics Forward-conduction region - corresponds to the on condition of the SCR where there is forward current from anode to cathode through the very low resistance SCR Characteristics Forward-blocking and reverse-blocking regions – correspond to the off condition of the SCR where the forward current from anode to cathode is blocked by the effective open circuit of the SCR SCR Characteristics Reverse-breakdown voltage, 𝑉𝐵𝑅(𝑅) - specifies the value of reverse voltage from cathode to anode at which the device breaks into the avalanche region and begins to conduct heavily Sample Problem Determine the gate trigger current and the anode current when the switch, SW1, is momentarily closed in the figure below. Assume VAK = 0.2V, VGK = 0.7V, and IH = 5mA. SCR Applications On-Off Control of Current – this circuit permits current to be switched to a load by the momentary closure of switch SW1 and removed from the load by the momentary closure of switch SW2 SCR Applications Half-Wave Power Control 120 V ac are applied across terminals A and B RL represents the resistance of the load R1 limits the current Potentiometer R2 sets the trigger level for the SCR SCR Applications When the SCR triggers near the beginning of the cycle (approximately 0°), it conducts for approximately 180° and maximum power is delivered to the load. When it triggers near the peak of the positive half-cycle (90°), the SCR conducts for approximately 90° and less power is delivered to the load. By adjusting triggering can be made to occur anywhere between these two SCR Applications extremes, and therefore, a variable amount of power can be delivered to the load. Figure (c) shows triggering at the 45° point as an example. When the ac input goes negative, the SCR turns off and does not conduct again until the trigger point on the next positive half-cycle. The diode prevents the negative ac voltage from being applied to the gate of the SCR. SCR Applications