As it can be seen in below schematics, I have a transformer connected to mains 220V and converts to 9V, which then connects to a bridge rectifier and voltage regulator through AC1
and AC2
labels.
This is a TRIAC control project and I am using the signal labeled SYNC
to let the microcontroller know about the zero-crossing points.
I am carrying AC1
and AC2
to the bridge rectifer from an another board through some breakaway connectors and a PCB, which in total is about 8 cm long trace per signal.
Do I need to put a small valued (about 100nF) capacitor across AC1
and AC2
? If so,where should I place this capacitor on the PCB, closer to the bridge rectifer or the transformer? How to calculate the voltage rating of the capacitor? What is the value of the capacitor needed?
What would be the purpose of this capacitor, in detail?
Edit:
I have not given a lot of details about R1 and C1 in the second schematic. I will try to give more information with this edit.
I am using D1 to isolate the filtered (DC) voltage so that I can have a zero-crossing detection signal. I wanted to have a 100 Hz, where my line frequency is 50 Hz. That's why I've taken the signal after the bridge rectifier.
Here are some scope-screen-shots of various configurations.
Secondary of the transformer*:
- R1 is populated, 7805 sourcing ~10mA
- R1 is populated, 7805 sourcing ~75mA
- R1 is not populated, 7805 sourcing ~75mA
Output of the bridge rectifier*:
- R1 is populated, 7805 sourcing ~10mA
- R1 is populated, 7805 sourcing ~75mA
- R1 is not populated, 7805 sourcing ~75mA
Input of 7805*:
- R1 is populated, 7805 sourcing ~10mA
- R1 is populated, 7805 sourcing ~75mA
- R1 is not populated, 7805 sourcing ~75mA
Signal labeled SYNC_In - R1 is populated, 7805 sourcing ~10mA
As you can see, in the scope-shot captioned Output of the bridge rectifier - R1 is not populated, 7805 sourcing ~75mA, voltage never goes down enough to create a SYNC_In
signal.
**:Image captions are from left to right and are listed below the related images. Clicking on the image caption will open up bigger resolution image in the same tab.*