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to make the revers biased p-n junction in SCR to be conducting.when we apply gate signal across gate and cathode it establish conducting part,thus the current from anode to cathode flow i.e main current.even after we remove the gate signal SCR in conducting mode because now this conducting path is maintain by main current i.e current from anode to cathode
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Why you use silicon not germanium in SCR?
because lekage current of silicon is less than germenium
What are applications of automatic battery charger using scr?
A Silicon Controlled Rectifier, commonly referred to as a SCR, is a semiconductor that allows current to flow through it only after a momentary positive voltage is applied to the gate. It also converts AC energy to DC energy. AC energy, or alternating current energy, sends the electrons in pulses, not creating a direct flow of electrons around the circuit. DC energy, or direct current energy, sends electrons in a steady flow around the circuit. A Silicon Controlled Rectifier has three leads that include the cathode, the anode, and the gate. Their main purpose is to ensure that electrons are flowing the correct way and to limit the amount of electrons that flow through. Before the gate is "opened", or has been touched by a positive current, the Silicon Controlled Rectifier acts as a wall and does not allow electrons to flow through. In a circuit, when wire leads are connected to the anode and the cathode of the Silicon Controlled Rectifier and an open wire lead has potential to be connected to the gate, it has the ability to stop almost all electrons from passing through or to let electrons pass through by touching the open wire lead to the gate. The three leads of the Silicon Controlled Rectifier play a very important role in how it works. An anode is a lead that the current flows into, and a cathode is a lead where the current flows out of. They send the electrons the correct way around the circuit. They also can stop the flow, or continue the flow, of electrons throughout the circuit. When they are connected, but no positive current has been given to the gate, they act as a break in the circuit that allows little light to get through. When electricity is applied to the gate, the electrons flow through the circuit the correct way and in the positive direction. The gate is what allows the Silicon Controlled Rectifier to turn on and send electricity through it. With a simple, direct touch of electricity, the gate opens and allows the electrons to flow through. The only way to stop the constant flow of electrons after the gate has been touched is to stop the circuit or take out the power source. There is no way to turn off the Silicon Controlled Rectifier after it has already been connected momentarily to a positive current of electrons. The gate is what allows the electrons to move directly throughout the circuit, and it cannot be stopped until the power source is disconnected or it shortens out. One example of a technology that a Silicon Controlled Rectifier is used for is a car alarm. When the car is in the state of being locked, and the window is smashed or the door is opened, it sets the alarm off. When you shut the door, the alarm still goes off, because there is no way to cut the power source without the keys to the car. The robber that broke into the car has no way of stopping the alarm unless he or she finds a way to disconnect the power source to the alarm. This is very useful because the alarm will most likely continue to go off, so the owner of the vehicle can be notified of a potential break in. Another example of a piece of technology that a Silicon Controlled Rectifier is used in is a battery charger. A SCR prevents
How do you calculate the current gain of a transistor JFET?
FETs don't have current gain as no current flows through the gate. The gain of a FET is a voltage gain and is called mu.
What is the difference between triac and scr?
== == == ==
How does an SCR power control circuit control a resistive load?
Two SCR's are connected in an inverse-parallel arrangement to one leg of a single phase circuit. This arrangement allows one SCR to control one half of the sine wave, and the other SCR controls the other. A special circuit is used, sometimes called a "trigger circuit". This circuit sends a pulsed signal to each gate of the two SCR's. The SCR's are so fast to open close the circuit, that they can be "fired" open, then "shut" off in increments far smaller than 1/60th of a second, the typical AC line frquency. So, if you were to tell the trigger circuit to fire each SCR for only 1/240th of a second, (1/2 of 1/2 of a complete cycle) 60 times a second, then each SCR would only be "on" or letting electric current through for 1/2 of each +/- cycle of the sine wave. Therefore output power would be 50% of maximum, but complete in the sense that the 60Hz cycle would remain intact. To put it another way you would still have an alternating current 60 times per second, but the upper and lower portion of the sine wave would be cut off early, and at the same points respectively. This is called Phase-Angle Control, and is the most common form of solid state power control. Resistive loads are the easiest to control with solid state techniques, though power factor is increased with the use of solid state switching. There are ways around that. The advantages of this type of power control is infinitley variable power output, with no mechanical contactors to wear out. SCR's can switch 100's of amps, hundreds of times per second, and as long as you keep them cool, theoretically they will never wear out. If you would like to know more, there is a site: http://www.payneb5.com , for Payne Engineering. They have a couple of animations and schematics depicting what i just explained, but with pictures.
How is an SCR turned off?
Once an SCR has been turned on by means of a gate pulse, it latches, or remains on. The only way to turn the SCR off is to either remove the anode to cathode voltage, remove the load current (SCR's have a minimum current below which they will not fire), or reverse bias the SCR. If the SCR is used in an AC circuit, turn off is easy. This is because the voltage falls to zero, then reverse biases the SCR every cycle. This naturally turns off the SCR. In fact, you have to re-trigger the gate every cycle to turn it back on. In a DC circuit, the SCR must be reset by some means as mentioned above. Once the SCR fires, there is nothing you can do to the gate to control the device. The gate only turns it on, not off. There is a similar device, called a GTO, or gate-turn-off device, that can be turned off via the gate. Once an SCR is on it will not turn -off unless the minimum holding current is met. that can be accomplished by reversing anode polarity or by decreasing loading to below holding current
The dc output of a controlled rectifier is controlled by?
A: An SCR does not produce DC per say but rather is the result of rectification. THE GATE will turn on the SCR when there is enough current available on the SCR. The SCR will not however shut of when the gate potential is reduced or removed. the two way to shut off an SCR is by removing the gate potential AND reducing holding current OR inverting the potential on the anode
What is the basic function of the SCR's gate electrode?
The SCR's gate electrode is used to turn the SCR on, i.e. fire it.
Define latching current in scr?
Latching Current is the minimum current needed on the gate to fire or trigger an SCR.
An SCR conducts appreciable current when Anode and gate are both negative?
No, an SCR conducts when the anode and gate are both positive.
Can a diac trigger scr?
No, a Diac cannot trigger an SCR because when the Diac turns ON, the current through the Diac is around 9 mA. The gate threshold current of an SCR is typically 5 mA, which is less. So the SCR can get damaged due to this high gate current.
What happens if gate voltage of an ON scr is decreased?
A: Nothing after an SCR conduct the gate has no more control to shut it off. So how do we shut off an SCR two way reverse the voltage on the SCR or reduce the current below the holding current. SCR are not DC friendly once on they stay on until see above
What happen when plus ve gate pulse given to reverse baise scr?
You cannot turn an SCR off by reverse biasing the gate. Once it is on (anode to cathode), it stays on until the forward current AND the gate current drops to the required threshold level. That said, you can pulse the anode negatively to turn an SCR off, so long as you don't exceed the reverse bias limits of the device. This is how (photographic) flash devices, for one example, can modulate the duration of the flash.
How do you turn on a silicon controlled rectifier?
In the usual circuit, a pulse of voltage on the gate electrode, providing a very small current, will cause a large current to flow from anode to cathode. The SCR will stay on until the anode current is reduced to zero (which may be because it's an AC supply). More at http://www.allaboutcircuits.com/vol_3/chpt_7/5.html ANSWER: By applying a gate current of significant magnitude the SCR will turn on, It not an amplifier it does not amplify current it just conduct with the gate current It is possible to have more gate current then current trough it, the shut off point need not be zero voltage it can be negative to the anode or the falls below the holding current
When An SCR conducts appreciable current?
And SCR will conduct appreciable current when it is gated "on" and thus "told" to conduct. A silicon controlled rectifier(SCR) is an electronically controlled DC switch, and the gate is the terminal to which the control voltage is applied. Use the link below to learn more.
How can you tell which is the gate terminal on an SCR?
Since the gate needs very small amount of current for operation the small terminal is the gate.
Why gate is closer to cathode in scr?
A: To partially eliminate the problems with cathode current hugging
