I have most of the lights in my living room run via Philips Hue bulbs. They look great, but there are a couple of old lights that I would like to integrate because they cannot be replaced by the Hue bulbs.

The first project will be a 12V LED strip (something like https://goo.gl/RE6WNl). I would like to use the electronics from a white Hue bulb (https://goo.gl/QJmzxs) as both the power supply and the remote dimmer, which would then integrate seamlessly into the Hue infrastructure.

I have opened one of the bulbs and found the two pins that provide the power. The issue is that they provide between 8V (for lowest dimmer setting) to 20V (for highest dimmer setting). So I will need to shift the voltage down by 8V and I am sorted (I think).

I have no background in electronics, but I think a buck converter will not work, because that would only give me a constant output. Also a voltage divider would not be ideal, as it only scales down the voltage (ie 4.8-12V) instead of reducing it by 8V.

I would appreciate any simple and effective solutions. The circuit would need to withstand around 24W.

Thanks!

 

Welcome to AAC.

they provide between 8V (for lowest dimmer setting) to 20V (for highest dimmer setting)

How did you measure that? The chances are that the bulb electronics use a variable duty-cycle pulsed waveform (PWM) to control brightness. Most DMMs give misleading readings when trying to measure such waveforms. Also, the use of PWM would mean you would need to reduce the duty-cycle to drop the 'average' volts by 8V.

Edit:
Furthermore, would your LED strip tolerate PWM with an 'average' 12V but much higher peak voltage?

 

And realize that the bulb circuitry is probably not isolated from the mains!
Connecting any external circuitry could be rather shocking.

 

Welcome to AAC.

How did you measure that? The chances are that the bulb electronics use a variable duty-cycle pulsed waveform (PWM) to control brightness. Most DMMs give misleading readings when trying to measure such waveforms. Also, the use of PWM would mean you would need to reduce the duty-cycle to drop the 'average' volts by 8V.

Edit:
Furthermore, would your LED strip tolerate PWM with an 'average' 12V but much higher peak voltage?

Thanks!

I measured the voltage with a standard DC voltmeter, while under load with a small section of LED strip. When not under load, the voltage reading is 58V, which might support your suspicion of a PWM driven LED(?)

I am not sure if the LED strip would tolerate that voltage for a long time, it did tolerate to be connected to the 8-20V output. At 8V it was dimmer than at 20V.

 

And realize that the bulb circuitry is probably not isolated from the mains!
Connecting any external circuitry could be rather shocking.

How can I test this? Thanks!

 

I suggest that you trace out the schematic of the electronics in the bulb and post it on the forum. There will be many forum members that will know from that if it is isolated. It is very unlikely that it will be isolated.

Les.

 

Isolation costs money, and is not needed for a bulb- no way is it isolated

 

This is pretty much exactly what I'm looking to do. I was planning to interface the hue bulb to a mosfet that adjusts a 12v power supply to dim or vary the pwm to my strip. My other thought was to use a buck voltage converter for the dimming and using the hue to set the output voltage. Don't leds like constant current? Maybe i could do a cc/CV buck converter and set a constant current. There are premade devices for smart dimming 12v strips, but they are like $50. I do have some schooling and experience with electronic. I also have an O-scope, so I should be able to check if it is pwm or not.

 

This is pretty much exactly what I'm looking to do. I was planning to interface the hue bulb to a mosfet that adjusts a 12v power supply to dim or vary the pwm to my strip. My other thought was to use a buck voltage converter for the dimming and using the hue to set the output voltage. Don't leds like constant current? Maybe i could do a cc/CV buck converter and set a constant current. There are premade devices for smart dimming 12v strips, but they are like $50. I do have some schooling and experience with electronic. I also have an O-scope, so I should be able to check if it is pwm or not.

Read post #3.

 

Read post #3.

I'm not sure why that really matters. I'm not going to be using the hue bulb to power the strip directly, only as a control signal. If it's that big of a deal, I could use an opto isolator to connect the control signal (hue bulb) to the power supply (or MOSFET). Especially easy if the hue is actually pwm. Could get really high tech and integrate a $3 arduino nano to map the brightness so 50% on the hue is actually 50% on the strip.

 

It most likely is based on PWM, linear LED dimming is not used very much.

Using a fast opto-isolator could be the ticket.
It probably uses a rather high PWM frequency, to preserve the dimming linearity, the opto-coupler should be very fast.

Hook the Hue lamp up to an isolation transformer and go hunting in there, tell us what you find.