SCR way of working

Status
Not open for further replies.
Z

ze

New Member
one thing that i did not understand was the way to turn off a scr!
you simply "wait" for to turn off?
when a gate current it given, the scr turns on, then i still behaves like an open circuit for how long?
it's until the sine wave reaches a certain value of voltage that the scr stops??
 
An SCR will begin to conduct when the proper voltage is applied to the gate, and will then continue to conduct until the forward bias is reduced to a point below the minimum level required for conduction.
 
ze said:
when a gate current it given, the scr turns on, then i still behaves like an open circuit for how long?
Click to expand...

BTW -- it behaves like a "closed" circuit rather than like an "open" circuit...
 

An SCR latches ON when triggered, it turns OFF when the current through it drops below it's 'holding current' - usually as a result of the zero crossing on the AC waveform.

To use an SCR on DC you have to reduce the current below the holding current yourself, this is usually done with a capacitor and a second SCR. As one SCR is turned on it turns the other one off by discharging the capacitor across it - the capacitor gives a reverse pulse to the SCR, reverse biasing it.
 

this is how the story goes......

when u apply a certain gate voltage the SCR "triggers". the result is that the SCR starts behaving like a short circuit. now if u want to turn the SCR off, u will have to decrease the current through the SCR below the holding current (Ih) level. that can be done by simply reducing the supply voltage.

once triggered, the SCR will behave as a short circuit until the current through it drops below Ih.
 
as i understood, then when the sine wave crosses zero the SCR turns off! so if i can control the time that an pulse is given in the SCR gate i can control the output current of the SCR RIGHT???
 
ze said:
as i understood, then when the sine wave crosses zero the SCR turns off! so if i can control the time that an pulse is given in the SCR gate i can control the output current of the SCR RIGHT???
Click to expand...

Yes, you need to detect the zero crossing point, then use a delay until you reach the point you want to trigger the SCR. You do this at every zero crossing point, that's twice per mains cycle.

Bear in mind, this method of power control is extremely noisey, you need to use plenty of filtering on the incoming mains supply.
 
yes thats how an SCR is used as a power controller. that is, the SCR controls the average power delivered to a load.

there are a number of ways in which u can control the power delivered to the load by an SCR. basically an RC circuit is used, the value of R determines the amount of power delivered to the load.

i hope that helps
 
Status
Not open for further replies.

Similar threads

S
  • Question
Cant get touch working on ILI9341 display with Teensy 4.1
Replies
8
Views
3K
Salchicha
S
A
  • Question
2n2222 transistor logic shifter not working
Replies
5
Views
3K
danadak
U
  • Question
What type of sensor is this?
Replies
2
Views
848
JimB
S
  • Question
Cant get ST7735 display working with Teensy 4.1
Replies
6
Views
2K
Salchicha
S
S
  • Question
Simplest way to detect when a person is home
2
Replies
29
Views
6K
eTech
E
Menu
Log in
Register
Cookies are required to use this site. You must accept them to continue using the site. Learn more…