Detecting zero crossing on secondary side of transformer.

[Sambo]

Can I detect power zero crossing on the low Voltage side of transformer by feeding the comparator on the pic with separately (half or full) rectified voltage?
Because I have the wave form in my head and I don't think I want to ( or even can ) ground circuit , I dint think 0V at the rectifier coincides with 0 V on the line.

On the other hand I may have to ground it if I want serial port connection to it?



Maybe it is not as important since I think I bought a zero crossing opto-triac but in case I have to use a different one....

As long as I can count the cycles maybe enough.


Cheers Sam.

 

[Phil Allison]

"Sambo"

Can I detect power zero crossing on the low Voltage side
of transformer by feeding the comparator on the pic with separately (half
or full) rectified voltage?

** Depends on the transformer.

Because I have the wave form in my head and I don't think
I want to ( or even can ) ground circuit , I dint think 0V at the
rectifier coincides with 0 V on the line.

** Most small AC supply transformers will have some phase error on the
secondary voltage compared to the primary.

Pick your transformer or trim the error out - if it matters in your app.




........ Phil

 

[Jamie]

Sambo wrote:

Can I detect power zero crossing on the low Voltage side of transformer
by feeding the comparator on the pic with separately (half or full)
rectified voltage?
Because I have the wave form in my head and I don't think I want to ( or
even can ) ground circuit , I dint think 0V at the rectifier coincides
with 0 V on the line.

On the other hand I may have to ground it if I want serial port
connection to it?



Maybe it is not as important since I think I bought a zero crossing
opto-triac but in case I have to use a different one....

As long as I can count the cycles maybe enough.


Cheers Sam.
Look up precision rectifier..

It's an op-amp usage that takes the AC and forms a nice full wave
output with very little loss at the valleys.


--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

 

On Nov 13, 9:52 am, Sambo <sa...@voidstar.com> wrote:

Can I detect power zero crossing on the low Voltage side of
transformer by feeding the comparator on the pic with separately (half

or full) rectified voltage?

Because I have the wave form in my head and I don't think I want to
( or even can ) ground circuit , I dint think 0V at the rectifier

coincides with 0 V on the line.

On the other hand I may have to ground it if I want serial port
connection to it?

Maybe it is not as important since I think I bought a zero crossing
opto-triac but in case I have to use a different one....

As long as I can count the cycles maybe enough.

Cheers Sam.

Cheap and dirty trick I've used is to add a series diode before the
first filter cap so that you have the raw output from the rectifier
diodes. You can resistively couple that into a comparator. As Phil
said there will be a phase shift but it might not be too troublesome.
For example, I use that to get the 120 Hz timing input to a digital
clock so the precise phase means nothing for that purpose.

GG

 

[Sambo]

stratus46@yahoo.com wrote:

On Nov 13, 9:52 am, Sambo <sa...@voidstar.com> wrote:
Can I detect power zero crossing on the low Voltage side of
transformer by feeding the comparator on the pic with separately (half
or full) rectified voltage?
Because I have the wave form in my head and I don't think I want to
( or even can ) ground circuit , I dint think 0V at the rectifier
coincides with 0 V on the line.

On the other hand I may have to ground it if I want serial port
connection to it?

Maybe it is not as important since I think I bought a zero crossing
opto-triac but in case I have to use a different one....

As long as I can count the cycles maybe enough.

Cheers Sam.

Cheap and dirty trick I've used is to add a series diode before the
first filter cap so that you have the raw output from the rectifier
diodes. You can resistively couple that into a comparator. As Phil
said there will be a phase shift but it might not be too troublesome.
For example, I use that to get the 120 Hz timing input to a digital
clock so the precise phase means nothing for that purpose.

GG

I was pondering that yesterday but I don't think that should work since once the cap charges ....

oh you mean additional diode between the bridge and cap , take input before the diode, and disregard tiny lateness for my ( at least for now ) resistive load.

I guess I'll go with that.

Cheers , Sam