LT1248 IAC pin not regulated to 2v

[Flyback]

Hi,
Why does the IAC pin of LT1248 not regulate to 2v...as attached.
LT1248 datasheet says 2v.

LT1248

https://www.analog.com/en/products/lt1248.html

Also, why does the sync input not work in syncing it?

 

[ronsimpson]

Why does the IAC pin of LT1248 not regulate to 2v

What does it do? Are you pulling up on the pin?

 

[Flyback]

This is the pin that "tells" the LT1248 where on the mains cycle we are.
So that the controller can adjust the current to get i in phase with v.
Its supposed to regulate to 2V, and then the LT1248 reads the current into the IAC pin (more current, higher mains instantaneous voltage must be).
But on the LTspice model, its nowhere near 2v.

IAC pin just has a resistor into it from the post rectifier bus positive.

 

[transconductance]

I don't think it's actually supposed to regulate itself to 2V. I think the data sheet is saying that the pin will be at 2V when there is no current into it. So that would be when DC+ is also at 2 volts. But, yeah, it's not clear.

 

[Flyback]

Thanks transconductance, i now see there is a 32k in the IAC pin...so that will be giving the voltage.