The thyristor is a type of diode that allows current to flow if and only if a control voltage is applied to its gate terminal. This type of diode has three electrodes: anode, cathode and gate. Thyristors have different operating principles depending on their classification. Generally, the thyristor is turned off and no current flows between the anode and cathode when there is no current flowing in the gate. On the other hand, when there is a current flow in the gate, it actually flows into the base of the npn transistor, which operates the thyristor. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get Original Essay Some of the significant points in this feature talk about the holding current, holding current, reverse current, and forward cut-off voltage. Holding current (IL) is the amount of anode current required to constantly maintain the operation of a thyristor immediately after turning it on. On the other hand, holding current (IH) is the current required to maintain a thyristor in its active state. In order to turn off a thyristor, the forward anode current must be less than its IH in a particular period of time. If not maintained properly, the thyristor will not return to its blocked state when the voltage between the anode and cathode increases again. In other words, if no GI is applied externally, there is a possibility or possibility of it returning to its conductive state. Reverse current (IR) will only be present and conduct through a device if and only if it is in a reverse biased condition. In most cases, current flows when the circuit is in a forward biased condition. However, there are cases where there is a reverse current that conducts in a reverse bias condition. Once the thyristor is triggered by a gate signal and its anode current is greater than the holding current, the device continues to conduct due to positive feedback even if the gate signal is removed. This is because the thyristor is a locking device and has been locked to the active state. The relaxation oscillator can be constructed via UJT. The UJT or Unijunction transistor is a break-over type transistor. It is composed of 3 terminals: Base 1, Base 2 and Emitter. UJT is said to be a transistor but it has different characteristics, properties and operation than the conventional BJT or FET because it is only used as a switch unlike some transistors like BJT and FET, it also allows the input signal to be amplified. Some of its applications are waveform generators, thyristor gate control, timers and oscillators. UJT is used in a relaxation oscillator because if you want to see its characteristics, it has a negative resistance region that can be easily used and employed in the relaxation oscillator. Please note: this is just an example. Get a custom paper from our expert writers now. Get a Custom Essay As technology continues to improve and develop, PUT was invented. PUT stands for programmable unijunction transistor. From the word itself, its structure and functioning are the same as UJT. It is said to be programmable because it can be tuned to a desired VP through external resistance and its intrinsic stall ratio. The resistor connected to the cathode terminal of the transistor limits the cathode current of the PUT. When VBB (supply voltage) is applied, the capacitor starts charging with the help of resistor R. Once the voltage across the capacitor exceeds the specified VP, the PUT.