QUOTE(ikengkai @ Feb 19 2016, 09:37 AM)
PWM? I thought they just use the current regulator circuit to maintain constant current to drive the LED, as current determine the LED brightness. Normal design will be a voltage step-down transformer, follow by current regulator / control circuit. I had heard some of the lighting shop tauke said: when u hold the LED bulb, the heavy will be better... I do not totally agree, but for layman, some sort an easy guidance.
agree..
so far most led bulbs in market using linear voltage supply(240 ac> rectify dc > stepdown tx > current limit resistor to match led array)..
the newer tear downs on youtube expose variable voltage supply divider with single npn transistor used by philips bulb and some other china manufacturer..
there is another option to use pwm to modulate the voltage using the common 555 timer ic to control npn transistor with an external resistor and capacitor.. i've seen this circuit on a cree xml t6 led..
right now its only on a flashlight but once the china manufacturers start using cloning this technology, their economies of scale will definitely drive the prices down.. pwm is the only logical choice as it improves the power efficiency above 80% as there is no heat wastage across resistors..
i.e voltage modulation via pwm vs linear voltage with current limiting resistor..
the force.. its calling ... to you..