Phase Locked Loop

[Charles Linquis]

At the moment I am detecting the zero crossing point by feeding the 3 phase into the input through high resistance chains.
Bob...

So, it sounds like you need a good zero crossing detector, not a PLL - correct?

I have lots of applications where I need to detect zero crossings and I use an opto-coupler like a MOCD207M (Fairchild) in a circuit with a 15K 2W resistor and a bridge rectifier. The transistor in the opto reliably turns off within 5 degrees on either side of the zero crossing. The LED is getting about 1mA at that point. If you increase the resistor's rating to 5W, you can use the same circuit for 120 and 240V. Use a 10K resistor in the collector of the opto.

[BobEdge]

Well I just read Darrels thread, & website on using instant interrupts. This should make what I want to do much easier. I can keep a running average of the frequency of the supply (which can dip using generators) then use the two opto method as in the paper to more reliably detect the zero cross point. Using a few timers to then sort out the firing of the thyristors.

Thanks to Darrel this may not be beyond me at all.

Just need to brush up on using hardware peripherals, rather than using PBP for ADC, timing etc.

Thank's for your ideas guys

Regards
Bob...