Hi,
It's been quite a while since i've done any hardware design, so would like to get some comments from the experts here.
The circuit uses 220VAC 50Hz, UK mains.
The circuit impliments an automatic dimmer switch, with a PIC controller at the heart going all the controlling etc., dimming from full on to full off in 16 steps, using a time delay after the zero-cross point (controlled by the PIC).
There are 3 areas of concern that i would like advice for;
1>
The mains cross-over zero detector circuit, in the middle-left of the diagram, made up of D2 and R3.
The theory here is that the PIC inputs have a current requirement of 33uA, so, for 5V input:
R = (12V - 5V - 0.6V) / 33u
= 6.4 / 33u
= 200k
Is this correct? The diode is to block the AC, therefore the PIC will get a change of state on the input pin every cross-over. The PIC inputs are protected internally against over and under voltage via protection diodes.
2>
The mains detection circuit, to the left of the diagram.
The mains 220VAC current is limited by R6/R7 (20k in total) then powers the AC opto-coupler.
The opto has a Vf of 1.5V, so to get 15mA current into the LEDs:
(1.414*220)-1.5
----------------
15mA
= 309.58 / 15mA
= 206k (200k)
The opto output then drives a transistor switch and the switching ripple is suppressed by the cap C8 (as the AC goes to zero, the LEDs will go off). I guessed a value for C8, is it about right?
This output is then fed to the PIC, and should be +5V when 220VAC is present, and 0V when the 220VAC is missing.
3>
The last part is the MOC3020 triac driver, and the L1 / C6 suppression circuit.
I'm using a BT136-600D triac, rated at 4A. Im expecting to switch no more that 3A.
Is this triac driver and suppression correct?