PLL Applications 1. Frequency Multiplication or Frequency Synthesis The block diagram of a frequency muliplier (or synthesizer) is shown in figure. In this circuit, a frequency divider is inserted between the output of the VCO and the phase comparator (PC) so that the loop signal to the PC is at frequency fOUT while the output […]
How a PLL works ? Consider VCO operating without input signal at free-running frequency fr and input signal of frequency fIN increasing from zero is applied to the PC. If the input frequency is less than fIN1, then the error voltage Ve is zero as illustrated in figure and VCO operates at a frequency fr.
MONOLITHIC PHASE-LOCKED LOOP (PLL) ICS Although the evolution of the PLL began in the early 1930s but its cost outweighted its advantage in the beginning. Today the PLL is even available as a single package, typical examples of which are the Signetic’s SE/NE series such as 560, 561, 562, 564, 565 and 567. They only
Operating principle of Phase Locked Loops The block diagram showing operating principle of PLLis given in figure. As illustrated in this fig, the PLL consists of a phase detector, a low-pass filter and a voltage controlled oscillator. YOU MAY ALSO REFER: PHASE LOCKED LOOP IC’s, DESIGN A PLL, PLL OPERATION, and PLL FM DEMODUATOR CIRCUIT Phase Detector A phase
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
The diacs, because of their symmetrical bidirectional switching characteristics, are widely used as triggering devices in triac phase control circuits emÂployed for lamp dimmer, heat control, universal motor speed control etc. Although a triac may be fired into the conducting state by a simple resistive triggering circuit, but triggering devices are typically placed in series
Introduction to Diac-Operation and Construction A diac is an important member of the thyristor family and is usually employed for triggering triacs. A diac is a two-electrode bidirectional avalanche diode which can be switched from off-state to the on-state for either polarity of the applied voltage. This is just like a triac without gate terminal, as
Applications of Triac Next to SCR, the triac is the most widely used member of the thyristor family. In fact, in many of control applications, it has replaced SCR by virtue of its bidirectional conductivity. Motor speed regulation, temperature control, illumination control, liquid level control, phase control circuits, power switches etc. are some of its
Characteristics of  Triac Typical V-I characteristics of a triac are shown in figure. The triac has on and off state characteristics similar to SCR but now the char acteristic is applicable to both positive and negative voltages. This is expected because triac consists of two SCRs connected in parallel but opposite in direc tions. MT2
Introduction to Triac-Its construction and Operation The triac is another three-terminal ac switch that is triggered into conduction when a low-energy signal is applied to its gate terminal. Unlike the SCR, the triac conducts in either direction when turned on. The triac also differs from the SCR in that either a positive or negative gate
The ability of an SCR to control large currents to a load by means of small gate current makes the device very useful in switching and control applications. A few of the possible applications for the SCR are listed in the introduction to SCR blog post. Here we will consider six applications of SCR like
How to make a full wave rectifier using SCR ? For full-wave rectification two SCRs are connected across the centre taped secondary, as shown in figure-a. The gates of both SCRs are supplied from two gate control supply circuits. One SCR conducts during the positive half cycle and the other during the negative half cycle
How SCR functions as a Half Wave Rectifier ? SCRs are very useful in ac circuits where they may serve as rectifiers whose output current can be controlled by controlling the gate current. An example of this type of application is the use of SCRs to operate and control dc motors or dc load from
How an SCR functions as a switch ? We have seen that SCR operates either in on-state or in off-state and no other state in between, that is SCR behaves like a mechanical switch. As such it is called electronic switch. An SCR has following advantages over a mechanical switch or electro-mechanical relay: Noiseless operation
90° Phase Control of SCR. In ac circuits, the SCR can be turned on by the gate at any angle a with respect to the applied voltage. This angle α is called the firing angle. Power control is obtained by varying the firing angle and this is known as phase control. In the phase-control circuit given in fig.
How to protect an SCR using protection circuits ? SCRs are sensitive to high voltage, over-current, and any form of transients. For satisfactory and reliable operation they are required to be protected against such abnormal operating conditions. Because of complex and expensive protection, usually some margin is provided in the equipment by selecting devices with
How to make series and parallel connections of an SCR ? In many power control applications the required voltage and current ratings exceed the voltage and current that can be provided by a single SCR. Under such situations the SCRs are required to be connected in series or in parallel to meet the requirements. Sometimes
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
