A voltage regulator is designed to automatically ‘regulate’ voltage level. It basically steps down the input voltage to the desired level and keeps that in that same level during the supply. This makes sure that even when a load is applied the voltage doesn’t drop. Thus, a voltage regulator is used for two reasons:- To […]
INTRODUCTION Almost all basic household electronic circuits need an unregulated AC to be converted to constant DC, in order to operate the electronic device. All devices will have a certain power supply limit and the electronic circuits inside these devices must be able to supply a constant DC voltage within this limit. This DC supply
Phase Locked Loops (PLL) Introduction to PLL The concept of Phase Locked Loops (PLL) first emerged in the early 1930’s.But the technology was not developed as it now, the cost factor for developing this technology was very high. Since the advancement in the field of integrated circuits, PLL has become one of the main building
Introduction to Operational Amplifiers In this post, the basics of an operational amplifier (generally abbreviated as op-amp) will be analysed along with its block diagram, basic structure, symbol, types and a detailed explanation of the typical op-amp. What is an operational amplifier (op-amp)? An op-amp is a multi-stage , direct coupled, high gain negative feedback
Programmable UJT (PUT). Programmable unijunction transistor or PUT is a close relative of the thyristor family. Its has a four layered construction just like the thyristors and have three terminals named anode(A), cathode(K) and gate(G) again like the thyristors. Yet some authors call it a programmable UJT just because its characteristics and parameters have much
UJT relaxation oscillator UJT relaxation oscillator is a type of RC ( resistor-capacitor) oscillator where the active element is a UJT (uni-junction transistor). UJT is an excellent switch with switching times in the order of nano seconds. It has a negative resistance region in the characteristics and can be easily employed in relaxation oscillators. The
How to trigger an SCR using UJT ? One common application of the uni junction transistor is the triggering of the other devices such as the SCR, triac etc. The basic elements of such a triggering circuit are shown in figure. The resistor RE is chosen so that the load line determined by RE passes
Current ratings of an SCR The current carrying capability of an SCR is solely determined by the junction temperature. Except in case of surge currents, in no other case the junction temperature is permitted to exceed the permissible value. Some of the current ratings used in industry to specify the device are given below. (i)
SCR Voltage Ratings (i) Breakover Voltage. The minimum forward voltage, when the gate is open, at which SCR starts conducting heavily (that is turned-on) is called the breakover voltage. To specify this value, the gate is in the open-circuit condition and the junction temperature is at its maxiÂmum permitted value, although VFB0 is still a
SCR-Ratings and Specifications The performance of an SCR is affected by the junction temperature, because of change in carrier densities in the four layers and the junction temperature naturally depends upon the internal power losses of the device and the efficiency of heat transfer mechanism. The factors contributing toward rise in junction temperature are on-state
Turning-off Methods of an SCR As already mentioned in previous blog post, once the  SCR is fired, it remains on even when triggering pulse is removed. This ability of the SCR to remain on even when gate current is removed is referred to as latching. So SCR cannot be turned off by simply removing the
How to turn ON an SCR ? As mentioned earlier, the SCR can be switched on either by increasing the forward voltage beyond forward break over voltage VFB0 or by applying a positive gate signal when the device is forward biased. Of these two methods, the latter, called the gate-control method, is used as it
Turn-on and turn-off characteristics of an SCR are called the dynamic characteristics of the SCR. (a)   Turn-On CharacterÂistic. The turn-on time characÂteristic shows the variation of current and voltage during turn-on. Turn-on time is defined as the time from the initiation of triggering, when the SCR offers infinite impedance to the flow of anode current, to
As already mentioned, the SCR is a four-layer device with three terminals, namely, the anode, the cathode and the gate. When the anode is made positive with respect to the cathode, junctions J1 and J3 are forward biased and junction J2 is reverse-biased and only the leakage current will flow through the device. The SCR
How an SCR works?-Principle of Operation SCR Working Principle The SCR is a four-layer, three-junction and a three-terminal device and is shown in fig.a. The end P-region is the anode, the end N-region is the cathode and the inner P-region is the gate. The anode to cathode is connected in series with the load circuit.
Introduction to SCR-Silicon Controlled Rectifier As the terminology indicates, the SCR is a controlled rectifier constructed of a silicon semiconductor material with a third terminal for control purposes. Silicon was chosen because of its high temperature and power capabilities. The basic operation of the SCR is different from that of an ordinary two-layer semiconductor diode
Comparison of  Thyristor and Transistor As already mentioned, transistors and thyristors are both semiconductor devices. They are now widely employed in switching operations because of their numerous advantages such as noiseless operation owing to absence of moving parts, very high switching speed (say 109 operations per second), high efficiency, low maintenance, small size, little weight
Comparison between Thyristors and Thyratrons Before the discovery of thyristors, thyratrons were used for industrial control, but now they have been replaced by the thyristors because of the following drawbacks of thyratrons. 1. Thyratron needs a large anode-to-cathode voltage and a separate filament supply whereas the thyristor needs only one main supply and a control
Thyristor Family-Types of Thyristors The P-N-P-N devices with zero, one or two gates constitute the basic thyristor. But today the thyristor family includes other similar multilayer devices also. The complete list of thyristor family members include diac (bidirectional diode thyristor), triac (bidirectional triode thyristor), SCR (silicon controlled rectifier), Shockley diode, SCS (silicon controlled switch), SBS
General Introduction to Thyristors and its Applications Thyristor is the general name given to a family of semiconductor devices having four layers with a control mechanism, although this term is most commonly applied to the SCR (silicon-controlled rectifier). This term is derived from thyratron and transistor because the device combines the rectification action of thyratron
JFETs and MOSFETs are quite similar in their operating principles and in their electrical characteristics. However, they differ in some aspects, as detailed below : JFETs can only be operated in the depletion mode whereas MOSFETs can be operated in either depletion or in enhancement mode. In a JFET, if the gate is forward biased,
Introduction to IGBT-Insulated Gate Bipolar Transistors Insulated gate bipolar transistor (IGBT) is a new high conductance MOS gate-controlled power switch. The fabrication process is similar to that of an N-channel power MOSFET but employs an N-epitaxial layer grown on a P+ substrate. In operation the epitaxial region is conductivity modulated (by excess holes and electrons)
MOSFET requires very careful handling particularly when out of circuit. In circuit a MOSFET is as rugged as any other solid-state device of similar construction and size. MOSFETs have an ultra-thin silicon dioxide layer between the channel and the gate. Because the insulating layer is so thin, it is easily destroyed by excessive gate source
All MOSÂ devices have insulated gates that are subject to voltage breakdown. For instance the gate oxide for Motorola CMOS devices is about 900 A thick and breaks down at a gate-source potential of about 100 V. To guard against such a breakdown from static discharge or other voltage transient, the protection networks shown in figure
Introduction to CMOS-Complimentary Metal Oxide Semiconductor FET’s Complementary metal oxide semi-conductor devices are chips in which both P-channel and N-channel enhancement MOSFETs are connected in push-pull arrangement. The basic connections for CMOS are shown in figure. Above figure shows various CMOS connections especially N-channel and P-channel CMOS connections. In this circuit, two MOSFETs (P-channel MOSFET and
