Obs Con.docx

1. generalization 2. observation 3. conclusion Exp 1 1. A silicon controlled rectifier or semiconductor controlled rectifier is a four-layer solid-state currentcontrolling device. SCRs can be triggered normally only by currents going into the gate as opposed to TRIACs, which can be triggered normally by either a positive or a negative current applied to its gate electrode. 2. A silicon controlled rectifier (SCR) is a four-layer solid state current controlling device with 3 terminals. They have anode and cathode terminals like a conventional diode and a third control terminal, referred to as the Gate. 3. The silicon controlled rectifier ( SCR ) is a three terminal semiconductor switching device which can be used as a controlled switch to perform various functions such as rectification, inversion and regulation of power flow. An SCR can handle currents upto several thousand amperes and voltages upto more than 1kV. Exp 2 1. TRIACs differ from SCRs in that they allow current flow in both directions, whereas an SCR can only conduct current in a single direction. ... In addition, applying a trigger at a controlled phase angle of the AC in the main circuit allows control of the average current flowing into a load (phase control). 2. Basically by controlling the firing angle means to manage the point on the AC signal waveform when the SCR is going to be triggered or in other words, the time corresponding to the AC signal waveform when the SCR gate is going to be given DC supply voltage. 3. Basic AC thyristor / SCR circuit. ... Once triggered the SCR will remain in its conducting state over the positive half of the cycle. As the voltage falls, there will come a point where the anode cathode voltage is insufficient to support conduction. At this point the SCR will stop conducting. Exp 3 1. 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. Again the terminal designations are arbitrary since the diac, like triac, is also a bilateral device. The switching from off-state to on-state is achieved by simply exceeding the avalanche break down voltage in either direction. 2. Diac Circuits Tutorial Testing. 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. ... An unusual characteristic is once the Diac goes into conduction, the resistance drops rapidly sometimes called negative resistance 3. We have successfully demonstrated the operation of the diac triac light dimmer circuit. With this circuit we have shown that one can regulate the intensity of a light using an AC source, and varying the

resistor used to determine the point in time that the triac conducts the AC wave through the light during each half cycle. In addition we have demonstrated the concept of a firing angle, α, and its relation to the RMS voltage applied to the light bulb.2. The DIAC is designed to have a particular break over voltage, and when a voltage less than this is applied in either polarity, the device remains in a high resistance state with only a small leakage current flowing. Once the break over voltage is reached however, in either polarity, the device exhibits a negative resistance. This is a bi-directional trigger diode used mainly in firing Triacs and Thyristors by the “phase control method in AC control circuits. Exp 4 1. Triacs are widely used in AC power control applications. They are able to switch high voltages and high levels of current, and over both parts of an AC waveform. This makes triac circuits ideal for use in a variety of applications where power switching is needed. One particular use of triac circuits is in light dimmers for domestic lighting, and they are also used in many other power control situations including motor control. As a result of their performance, trials tend to be sued for low to medium power applications, leaving thyristors to be used for the very heat duty AC power switching applications. 2. it helps to have an understanding of how a thyristor works. In this way the basic concepts can be grasped for the simpler device and then applied to a triac which is more complicated. The operation of the thyristor is covered in the article in this section and accessible through the "Related Articles" box on the left of the page and below the main menu. For the operation of the triac, it can be imagined from the circuit symbol that the triac consists of two thyristors in parallel but around different ways. The operation of the triac can be looked on in this fashion, although the actual operation at the semiconductor level is rather more complicated. 3. But for this condition the load current through the TRIAC should be greater than or equal to the latching current (IL) of the TRIAC. So to conclude a TRIAC will remain turned on even after removing the gate pulse as long as the load current is greater than the value of latching current. Exp 5 1. TRIACs differ from SCRs in that they allow current flow in both directions, whereas an SCR can only conduct current in a single direction. ... In addition, applying a trigger at a controlled phase angle of the AC in the main circuit allows control of the average current flowing into a load (phase control). 2. The triac would be fired late and only a portion of the power would be delivered to the load. Conclusions: ... It can be turned on by a pulse of gate current but does not require the breakover voltage to initiate conduction like the diac. Unlike an SCR, the triac is designed to conduct on both halves of the AC waveform. 3. A resistor is also connected in series to reduce the gate current applied by the opto-Triac. Such a solution is good for all Triacs. The device is then triggered by a positive gate current when the voltage across the Triac, just before turn-on, is positive, and by a negative current in the reverse situation. Exp 6

1. The static characteristics of unijunction transistors are exhibited by two surfaces in three-dimensional space. This representation is employed to examine a general formulation of the problem of analysis and design with a device that is characterized by a nonlinear relationship among four variables. 2. The unijunction transistor is a solid state triggering device that can be used in a variety of circuits and applications, ranging from the firing of thyristors and triacs, to the use in sawtooth generators for phase control circuits.The negative resistance characteristic of the UJT also makes it very useful as a simple relaxation oscillator. 3. The unijunction transistor is a solid state triggering device that can be used in a variety of circuits and applications, ranging from the firing of thyristors and triacs, to the use in sawtooth generators for phase control circuits.