Led Driver, Dimmable ?

[Wp100]

Hi,

Been landed with a little problem, but not sure if I can solve it on my own .

Its a cheapo ebay aquarium led lighting unit, just 14W but it does not have any means to create a dimmable sunrise/sunset action , as I do on my own 12v pwm driven aquarium led unit.

Have opened up the little power supply / controller and seems its a dedicated mains to led driver system that outputs 110v to the leds .

Have found the chips datasheet, but does not look like it has any input for a pwm signal.

What I do not know, is can we use a separate pwm signal feeding a mosfet on the 110v line to to leds, or will that interfere with the led drivers actions ?

To be honest I am a little dubious about the quality of the controller with its mains input, though it does have a miniature fuse.

Perhaps the best option might be for them to buy a better unit ?

 

[rjenkinsgb]

It's basically a switched mode supply controlled entirely by output current, with feedback via the CS pin.

Hypothetically, if you connect a resistor in series with the current sense resistor and the CS pin (eg. 1K) then connect another resistor from the VCC pin to CS via the transistor of an opticoupler, you can control the output, reducing it by artificially increasing the CS voltage above the actual voltage on the sense resistor.

With 1K series you only need 0.4mA bias to shut it off.
A 39K resistor should be pretty close.

Either varying the current in the opto LED or using high frequency PWM should control the lamp brightness, from normal to zero or near that.

It's a totally untested idea so it may also destroy the lamp! But hopefully not...

 

[Wp100]

Thanks, it does not really seem like a realistic option for experimentation, given the small smd circuit we have there.

Think we are moving towards leaving the lamp as it is, just automating the on /off of the mains supply and making up another smaller led array with pwm just to act as sunrise/sunset so its not as startling for the tank inhabitants etc.