What is wrong with this circuit?

Thread Starter

GEMEYatin

Joined Nov 27, 2021
2
As I was testing this circuit practically with 100 watt bulb 230 V 50 Hz mains as a load initially the circuit worked as expected but after some time small amount of current started to flow which was enough to dimly light the filament even if 5 V is not provided and 5 V pin is grounded. I have also tested this after disconnecting the capacitor but that also does not improved the situation.
 

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bertus

Joined Apr 5, 2008
21,761
Hello,

The resistors at the gate are to high and there is no gate turnoff resistor.
Have a look at this circuit form the datasheet:
MOC3041_circuit.png
Bertus
 

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Thread Starter

GEMEYatin

Joined Nov 27, 2021
2
Hello,

The resistors at the gate are to high and there is no gate turnoff resistor.
Have a look at this circuit form the datasheet:
View attachment 253695
Bertus
Even with the current circuit initially it was working perfectly and only after sometime circuit started to act up. Why is that? Also as there was no 360 ohm resisyor was avaliable and only minimum of 1k resistor was avaliable, thats why I have used two 1k resistors in parallel.
 

Austhinker

Joined Apr 7, 2021
5
As I was testing this circuit practically with 100 watt bulb 230 V 50 Hz mains as a load initially the circuit worked as expected but after some time small amount of current started to flow which was enough to dimly light the filament even if 5 V is not provided and 5 V pin is grounded. I have also tested this after disconnecting the capacitor but that also does not improved the situation.
If the BT136 triac is faulty/off-spec it could give this result. Normally, the maximum off-state leakage current through the BT136 triac is specified at 0.5mA (at 125°C junction temperature), which would only give about 0.9mW through the bulb, however if the triac is exceptionally leaky the wattage would go up. As the triac warmed the current would increase, and as the bulb warmed the resistance would increase, increasing the wattage heating the filament, which could account for the the time delay.
 
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