Hi,
The simulation shows that point 'A' on your diagram shows a voltage high spike when the Vcc goes from 0V to the Vcc value.

As you can see from the plot, Vgate is partially high, before Vcc goes high, then it jumps to a higher voltage level as Vcc is applied.

Is that what you are asking.?
E

 

we can make it to be 0V originally, why not?

Yes, you can short out the SCR, but for what reason?

I still don't know what it is you are trying to understand.

Bob

 

Hi,
The simulation shows that point 'A' on your diagram shows a voltage high spike when the Vcc goes from 0V to the Vcc value.

As you can see from the plot, Vgate is partially high, before Vcc goes high, then it jumps to a higher voltage level as Vcc is applied.

Is that what you are asking.?
E

Hi,
The simulation shows that point 'A' on your diagram shows a voltage high spike when the Vcc goes from 0V to the Vcc value.

why is like that?

 

As you can see from the plot, Vgate is partially high, before Vcc goes high, then it jumps to a higher voltage level as Vcc is applied.

I think vg is added from outside, not decide by vs.

 

Yes, you can short out the SCR, but for what reason?

I still don't know what it is you are trying to understand.

Bob

to see how it goes up to on scr

 

If you hold point A at 0V, the SCR can never be on. You are not making any sense.

Bob

 

If you hold point A at 0V, the SCR can never be on. You are not making any sense.

Bob

maybe I'm wrong. I mean weather there are parasitic capacitors in charge to lift va and on scr.

 

I think BG is added from outside, not decide by vs.

Hi,
Look at the sim circuit you will see that the Vgate is Enabled by the 6V driving current thru the R2 resistor, then thru the Gate tthen via the SCR internal resistance to 0v.

This gives a voltage at the Gate of approx 600mV. [It is Enabled]

When the Vcc is applied, the extra current thru the SCR raises the Gate voltage to approx 800mV

E

 

Perhaps this answers your question. Staring Vcc at 0 and ramping it up, here is what happens to the voltage at A. As to whether there is a parasitic capacitance, yes, there is always a parasitic capacitance in every circuit element. Usually, it can be ignored.

Bob

 

Hi,
Look at the sim circuit you will see that the Vgate is Enabled by the 6V driving current thru the R2 resistor, then thru the Gate tthen via the SCR internal resistance to 0v.

This gives a voltage at the Gate of approx 600mV. [It is Enabled]

When the Vcc is applied, the extra current thru the SCR raises the Gate voltage to approx 800mV

E

I think this involves inner structure of scr. still don't know how 600MV and 800MV come.

 

Perhaps this answers your question. Staring Vcc at 0 and ramping it up, here is what happens to the voltage at A. As to whether there is a parasitic capacitance, yes, there is always a parasitic capacitance in every circuit element. Usually, it can be ignored.

Bob

View attachment 251974

yes, that's what I think. and now I'm wondering about va spike(fig eg984) it goes to 0v again, and scr still on , right?