Choppers and Types -Ac and DC Chopper Circuits

8/11/2014 Choppers and Types -Ac and DC chopper circuitshttp://www.circuitstoday.com/choppers-an-introduction 1/14 Custom Search Home Forums Datasheets Lab Manual Testing Components Buy Project Kits Electronic Circuits and Diagram-Electronics Projects and Design Search Choppers – A general introduction Arun January - 25 - 2012 4 Comments Choppers A chopper is basically a dc to dc converter whose main function/usage is to create adjustable dc voltage from fixed dc voltage sources through the use of semiconductors. Types of choppers The main classification of the types of choppers is given in another post. Take a look - TYPES OF CHOPPER CIRCUITS There are two types of choppers – AC and DC. AC Link Chopper In the case of an ac link chopper, first dc is converted to ac with the help of an inverter. After that, AC is stepped-up or stepped-down by a transformer, which is then converted back to dc by a diode rectifier. Ac link chopper is costly, bulky and less efficient as the conversion is done in two stages. DC Chopper A DC chopper is a static device that converts fixed dc input voltage to a variable dc output voltage directly. A chopper can be said as dc equivalent of an ac transformer as they behave in an identical manner. This kind of choppers are more efficient as they involve one stage conversion. Just like a transformer, a chopper can be used to step up or step down the fixed dc output voltage. Choppers are used in many applications all over the world inside various electronic equipments. A chopper system has a high efficiency, fast response and a smooth control. Principle of Chopper Operation 8/11/2014 Choppers and Types -Ac and DC chopper circuits http://www.circuitstoday.com/choppers-an-introduction 2/14 A chopper can be said as a high speed on/off semiconductor switch. Source to load connection and disconnection from load to source happens in a rapid speed. Consider the figure, here a chopped load voltage can be obtained from a constant dc supply of voltage, which has a magnitude V s. Chopper is the one represented by “SW” inside a dotted square which can be turned on or off as desired. Output Voltage and Current Waveforms Let us now take a look of the output current and voltage wave forms of a chopper. During the time period T on the chopper is turned on and the load voltage is equal to source voltage V s . During the interval T off the chopper is off and the load current will be flowing though the freewheeling diode FD . The load terminals are short circuited by FD and the load voltage is therefore zero during T off . Thus, a chopped dc voltage is produced at the load terminals. We can see from the graph that the load current is continuous. During the time period T on , load current rises but during T off load current decays . Average load Voltage is given by V 0 = T on / (T on +T off ) * Vs = (T on /T) V = A V s ………………(1.0) T on : on -time T off : off- time T = T on +T off = chopping period A = T on /T = duty cycle So we know that the load voltage can be controlled by varying the duty cycle A. equation 1.0 shows that the load voltage is independent of load current it can be also written as V 0 = f. T on .V s f= 1/T = chopping frequency Step – up Choppers 8/11/2014 Choppers and Types -Ac and DC chopper circuits http://www.circuitstoday.com/choppers-an-introduction 3/14 In the case of the chopper circuit (Refer figure named – “chopper circuit”) shown in beginning of this article, V 0 or the average output voltage is less than the input voltage V s so this type of chopper is called a step down chopper. For a step-up chopper we can obtain an average output voltage V 0 greater than input voltage. Figure (a) shows the elementary form of a step-up chopper. Working Principle of a Step-up Chopper In step-up chopper a large inductor, L is in series with the source voltage V s . This forms a closed path as shown in the figure (b). During the time period T on the chopper is on the inductor stores energy. When the chopper is turned off the current is forced to flow through the diode and load for a time T off and as the inductor current cannot die suddenly. When the current decreases the polarity of the emf induced in L is reversed. Fig (c). As a result the total voltage available across the load is given by the equation V 0 = V s + L (di/dt) . The voltage V 0 exceeds the source voltage and hence the circuit acts as a step-up chopper and the energy which is stored in L is released to the load. Voltage and current waveforms 8/11/2014 Choppers and Types -Ac and DC chopper circuits http://www.circuitstoday.com/choppers-an-introduction 4/14 When the chopper is turned ON the current through the inductance L will increase from I 1 to I 2. As the chopper is on the source voltage is applied to L that is v L = V S . When the chopper is OFF, the KVL for the figure (c) can be written as v L - V 0 +V s =0 or v L =V 0 -V s where v L is the voltage across L. Variation of source voltage v S , source current I S , load voltage v 0 and load current i O is sketched in the fig (d) . Let us assume that the variation of output current is linear, the energy input to inductor from the source, during the time period T on , is W in = V s (I 1 +I 2 /2) T on During the time T off the chopper is off, so the energy released by the inductor to the load is W off = (V 0 -V s )(I 1 +I 2 /2).T off Let us assume that the system is lossless, then the two energies say W in and W off are equal. So equating these two we will get V s (I 1 +I 2 /2) T on = (V 0 -V s )(I 1 +I 2 /2).T off V s T on = (V 0 -V s ) T off V 0 T off = V s (T off + T on ) = V s .T V 0 = V S (T/T off ) = V S (T/T-T on ) =V S (1/(1-A) ………….(2.0) From the equation 2.0 we can see that the average voltage across the load can be stepped up by varying the duty cycle. If the chopper in the figure (a) is always off, A=0 and V 0 = V s . If the chopper is always on, A =1 and V 0 = infinity as we can see from the graph. In practical applications the chopper is turned on and off so that the required step- up average output voltage, more source voltage is obtained. 8/11/2014 Choppers and Types -Ac and DC chopper circuits http://www.circuitstoday.com/choppers-an-introduction 5/14 Custom Search Figure shows variation of load voltage V 0 with duty cycle . Application of Step-up Chopper Figure shows regenerative braking of dc motor. The principle of step-up chopper can be used for the regenerative braking of DC motors. The armature voltage E a is analogy to the V S and voltage V 0 is the dc source voltage. When the chopper is on the inductor L stores the energy and when it is off the inductor release the energy. If E a / (1-A) exceeds V 0 , the dc machine will work as a dc generator and the armature current will flow in a direction opposite to the motoring mode. As the power now is flowing from dc machine to the source V 0 it will cause regenerative breaking of the dc motor. Even at decreasing motor speeds, regenerative breaking can be provided as the motor armature E a is directly proportional to the field flux and motor speed. You may also like: Types of Chopper Circuits We recommend: Oscillators-An introductory blog post Digital thermometer circuit Ultrasonic range finder using 8051 TDA7294 100W Audio Amplifier Characteristics of a UJT Search Posted in Power Electronics Tags: Power Electronics Leave a Reply Name (required) Mail (will not be published) (required) 8/11/2014 Choppers and Types -Ac and DC chopper circuits http://www.circuitstoday.com/choppers-an-introduction 6/14 Website Submit Comment 4 Responses to “Choppers – A general introduction” Mahendra Patil says: March 28, 2014 at 5:59 am Is this same same as clipper and clamper circuits ? Reply MATHEWS KURIAN says: August 2, 2013 at 9:52 pm But why at all we should use this power supply when new technology SMPS supplies are available in ample range. Reply MATHEWS KURIAN says: August 2, 2013 at 9:53 pm The actual purpose of using this type of power supply is not explained here. Reply muhhamadsadiqali says: April 19, 2013 at 7:22 pm much more knowlge about electronics thankyou Reply Get Daily Updates via Email Enter your email Subscribe Latest Articles Tachometer using arduino Interfacing LCD to arduino Motor speed control using arduino Digital code lock using arduino Interfacing hex keypad to arduino Digital thermometer using arduino Temperature logger using arduino Ultrasonic range finder using arduino Voltmeter using arduino PWM Control using Arduino – Learn to Control DC Motor Speed and LED Brightness 8/11/2014 Choppers and Types -Ac and DC chopper circuits http://www.circuitstoday.com/choppers-an-introduction 7/14 Categories 101-Announcements 555 Timer IC 8051 8051 projects Amplifier Circuits Arduino Audio Circuits Automotive Circuits AVR Basic Electricity Basic Electronics Battery Circuits C plus plus C Programming Cable TV Circuits Camera Technology Clipping and Clamping Circuits Clocking & Timer Circuits Conversion Circuits Counter Circuits Counters Digital Electronics Education & Training Electronic Components Electronic Keys & Locks Electronics Books Electronics Jobs Embedded Systems Equipment Reviews Events Fan Circuits Filter Circuits Fire Alarm Fun & Game Circuits Gadget Reviews Ham Radio Circuits High Voltage Circuits History Home Circuits Industrial Circuits Instruments Integrated Circuits Inverters Lab Manuals LED related Light Related Lighting Circuits MATLAB Microcontrollers Mobile Phone Related Motor Related Nanotechnology Oscillators Peripheral Interface Controller (PIC) 8/11/2014 Choppers and Types -Ac and DC chopper circuits http://www.circuitstoday.com/choppers-an-introduction 8/14 Power Controller Circuits Power Electronics Power Supplies Project Ideas Projects Proximity Detectors Radio Circuits Radio Transmitters Raspberry Pi Relays Remote Circuits Reviews Robotics RTOS Security & Saftey Sensor Circuits Signal Conditioners Signal Generators Speed Controller Circuits State space analysis Switching Circuits Tech News Telephone Related Television Related Temperature Related Test & Measurement Circuits Testing Components Three phase circuits Timer Circuits Tone generator circuits Tools and Softwares Transmitters Tutorials UPS USB Circuits Videos VLSI Voltage Regulators Like Us on Facebook Circuitstoday.com 23,590 people like Circuitstoday.com. 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