[SOLVED] 74LS74 D flip flop state changing automatically

[D.A.(Tony)Stewart]

, can you please explain how will a zero crossing triac and a RC snubber will help to remove noise spikes?

Relays are asynchronous and can switch during worst case peak voltage or worst case peak current during off. A Triac shuts off near zero current crossing to minimize EMI when turned off.

ZCS (zero crossing switch) type Triac turns on at 2 PN junction drops or near 0V voltage. This reduces turn-on slew rate of current.

First try 50 Ohm 1W in series with 1kV polyester across contacts. This is not safe to touch live when switched off but suppresses transient. Triac is a better solution with built-in dv/dt protection to prevent false trigger from external glitches on line.

 

[RohanDey]

Relays are asynchronous and can switch during worst case peak voltage or worst case peak current during off. A Triac shuts off near zero current crossing to minimize EMI when turned off.

ZCS (zero crossing switch) type Triac turns on at 2 PN junction drops or near 0V voltage. This reduces turn-on slew rate of current.

First try 50 Ohm 1W in series with 1kV polyester across contacts. This is not safe to touch live when switched off but suppresses transient. Triac is a better solution with built-in dv/dt protection to prevent false trigger from external glitches on line.

I have built 4 such boards using a ZCS Optocoupler (MOC3061) and a 4 Amp Triac (BT136). All of them seems to work properly without any disturbance. I have used the same circuit as given on the MOC3061 datasheet and I have put a snubber circuit also as you have recomended. I have tested this boards for 2 to 3 days, 10 to 12 hours per day, and everything seems to work fine. Thanks for your help.

I have one question. I am keeping the Optocoupler ON continuously while in ON state instead of giving short pulses. Will this damage the MOC or the Triac in the long run?

 

[milan.rajik]

I am keeping the Optocoupler ON continuously while in ON state instead of giving short pulses. Will this damage the MOC or the Triac in the long run?

Whether you keep it ON all time or off or give pulses of different width doesn't matter. It will not harm the MOC circuit.

 

[RohanDey]

Whether you keep it ON all time or off or give pulses of different width doesn't matter. It will not harm the MOC circuit.

Thanks for your reply