I started with the classic triac dimmer and while it's good for a conventional bulbYou can't dim with PWM a device which is connected to the power line.
You do phase control.
In its simplest terms, you synchronize to the zero crossing and delay the triggering a few milliseconds. That delay sets your brightness.
And the semiconductor device is a Triac, not a transistor. Can also be done with a pair of SCRs.
And the optocoupler has a Triac output, not a transistor output.
Google "Triac dimmer".
Firstly, make sure the GU10 LED bulbs are truly dimmable. Most already have a switching current regulator in them which will interfere with the drive signal from your circuit.
I think it is unlikely you have sufficient base current in the BUX87 to provide reliable switching. Because most of the base current comes from C7 discharging, you may need a much bigger value and possibly a lower value for R7. Increasing C7 alone may work at low PWM ratio because it has longer to charge but at full brightness, all the base current has to flow through R7 and the optocoupler. A MOSFET might be a better option simply because at low frequency it requires little gate current.
The NE555 will not give you a complete 0% to 100% pulse/space ratio anyway. A small MCU with an ADC feeding a PWM generator will give you full range with fewer components but you will need some simple software. (read ADC --> write PWM)
It would be wise to add some resistance in series with the 'PWM PS' 220nF capacitor in case it goes short circuit!
Just my thoughts....
Brian.
A dimmable LED lamp means it has an internal control circuit that recognizes the shape of 'chopped' phase control signals or uses PWM derived from its own internal controller. It doesn't necessarily mean it responds to changes in input voltage or fast switched voltage pulses. Temporarily substitute your LED with an incandescent lamp, it that works it means your dimmable LED is the problem.Yes the bulbs are of course dimmable!
Ohh good idea...! I tried it on Spice and it works like a charm, thanks a lot..!You can alternatively drive the 555 charge/discharge resistors by OUT pin, leaving DIS pin unconnected.
I guess it's rather an issue as interfering with the bulb electronicsSome flickering can be expected due to 500 Hz pwm running asynchronous to 50 Hz mains.
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