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It is a current
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∙ 8y ago
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How do you calculate holding current of scr when latching current is given?
we know that ratio of holding current to latching current in scr is 0.4.
Define latching current in scr?
Latching Current is the minimum current needed on the gate to fire or trigger an SCR.
What is the difference between an SCS and an SCR?
An SCS has an additional gate - the anode gate. It is physically smaller than an SCR and has smaller leakage and holding currents than an SCR.
Is scr current controlled device?
yes it is current controlled
Why SCRs are connected in parallel?
When the load current exceeds the SCR current rating, SCRs are connected in parallel to share the load current. Further the holding currents of the devices should not be so much different that at reduced load current one of the device gets turned-off because of fall of current through it blow its holding current value.
How do you calculate holding current of scr when latching current is given?
we know that ratio of holding current to latching current in scr is 0.4.
What is holding current?
it is the minimum current required to maintain the SCR in conducting state.
What happens if voltage is constant and current is varying when an scr triggers?
Even if the current is varying,as long as the current reaches the value required to trigger the SCR, it will snap into operation. The SCR will remain in operation until the current through it drops to a value below the holding 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
Why scr is not suitable for dc circuit?
A: It is OK if a way to insure that the SCR can be shut off otherwise it will conduct forever. the only way to shut off an SCR while is on is to reduce the current below them holding current point or by reversing the polarity briefly
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 effect of holding current in SCR?
The effect of holding current (anode to cathode) in an SCR is to retain the turned on state, even in the absence of any gate voltage. When used as an AC voltage controller, the SCR conducts from the moment the gate and anode goes positive until the anode goes negative on the next zero line crossing, irrespective of any further transistions on the gate.
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
Define latching current in scr?
Latching Current is the minimum current needed on the gate to fire or trigger an SCR.
What two things must happen to cause an silicon controlled rectifier to fire?
You must have a voltage on the gate that exceeds the turn-on threshold of the SCR. Typically around 0.65v. Then you must maintain a minimum holding current from Anode to Cathode. Once turned on, the SCR will remain self latched in the on state until the current through the Anode and Cathode falls below the minimum self holding current.
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.
Is scr current controlled device?
yes it is current controlled
