Help me identify the function of a resistor and a cap in an AC circuit

I'm looking at an AC circuit that has a resistor and cap in parallel across the line voltage.
My guess is that this is a noise filter but .... just a guess. I attached a circuit snippet. The rest of the circuit is buffered from the snippet by 2 series resistors and a half wave diode.

If anyone knows how C2 and R1 are used and how to calculate the size, please help!

-NN

noise filter circuit

post the whole circuit... my guess is the capacitor is used for low pass filtering the input i.e. removing the high frequency noise by knowing the maximum frequency of the input...

60hz noise filter

Yes, it is a low pass filter. It should be a ceramic one ( I see a plus sign near the cap C2 it should not a electrolytic or polarized capacitor). A simple way of calculating this capacitor is through capacitive reactance. i.e. Xc=1/2пfc

60hz filter circuit

Hi,
Functionally it looks like a transcient absorber. If the same 230V line is shared between an inductive load and a sensitive control circuit, when you swith off the mains, this capacitor will smoothenout the switching process keeping the voltage below arcing level and the resistor will provide a path to dissipate the stored energy. Depending on the value of inductance and operating current, manufacturers will generally specify values for R and C. Another alternative is to use a transorb in the place of R and C.
Regards,
Laktronics

60 hz noise filter

C2 is noise filter and R1 for discharging C2 when disconnecting from mains.

60 hz filter

Thanks for all the replies.

This circuit is the beginnings of a transformerless 120VAC -->5VDC supply.

I got it from this app note which details a heater controller circuit (page 7) :
**broken link removed**

Then after building the Vsupply part of the circuit and getting some really hot (silicone type) 1K, 5W resistors with Microchip's design, I read about this further and changed my supply design to be capacitive:
R6 is 1K, 5W silicone, C1 is 250V, 0.1F- it's what I have handy.
**broken link removed**

I have attached an updated circuit snippet to this post. I removed the resistor/cap network for now although I will be putting it back once I connect the AC load.
So in order to calculate for C as a lowpass line filter, it is 1/2*pi*60*Xc ? How do I know what Xc should be? And if I am using the resistor as a timer, what value is reasonable?
LAKTRONIC: The load will be resistive. So would I still need to use a Transorb?

Thanks!
-NN

noise site:edaboard.com

Hi,
That's it, all functions are clear from the app. notes. The capacitor is to filter out high frequency noise from the mains, which otherwise may affect the functioning of the sensitive microcontroller circuit. The parallel resistance is to discharge the capacitor charged to the mains voltage, should you switch off the mains during a non-conducting phase of the triac.
You also notice a 'MOV' in the circuit which is the transorb used to limit the peaks of wider transients on the mains.
I hope you are fully aware of the saftey hazards of the circuit, the floating mains voltage is present on all parts of the circuit including microcontroller pins and you should stick "DANGER- HIGH VOLTAGE" label all over the circuit. You can not connect the controller ground to safety earth.
Though it is a nice academic project, you will learn the hardway that the good old low cost mechanical solution was more robust to mains transients, lightning strikes and rough usage/environment as compared to an electronic solution.
Regards,
Laktronics

capacitor for 60 hz noise

Thanks Laktronics!

Yes I am using a MOV and am aware of safety.
Wearing safety goggles on power up

Can you explain further what you mean by not connecting the controller to earth ground? How will I ground it then?

*edit: Did you mean a transorb by "low cost mechanical solution"? I have no objections to this. Easier to wire.

Cheers!
-NN

Added after 3 hours 53 minutes:

Have built this circuit with many problems..started a new thread...
-NN