LED Voltage dimming help

[dtaflorida]

I have some G4 LED discs which are halogen replacement bulbs. They say on the box 12V-30V. Amazon listing says they're not dimmable though. What does that mean? Non-dimmable via PWM?

 

I tried powering them at different voltages and that does change the brightness.

 

So would it be safe to find some way to vary the voltage? Safe as in they won't catch fire, I don't mind much if their lifespan is shortened a little as long as they'll last a year.

 

If so, what AC/DC adapter or other thing would I need to make the voltage adjustable without/minimal heat generation? It doesn't need to be something flashy, just some way I can set it and forget it. Heat is something I'd like to avoid.

 

[Hackentosher]

The led probably has some kind of LDO voltage converter on board. From what I understand, you need a super clean power source to drive chip leds like that thus an LDO will provide a clean, say 8v. However it can take up to 30v which I would assume is the max input voltage of the regulator. 

[dany_boy]

You could probably use a buck converter to output lower voltages say something between 6-12v. That way the regulator inside the bulb will be limited to the input voltage, whether its a switching or a linear one.

[Unimportant]

2 hours ago, dtaflorida said:

I have some G4 LED discs which are halogen replacement bulbs. They say on the box 12V-30V. Amazon listing says they're not dimmable though. What does that mean? Non-dimmable via PWM?

 

I tried powering them at different voltages and that does change the brightness.

 

So would it be safe to find some way to vary the voltage? Safe as in they won't catch fire, I don't mind much if their lifespan is shortened a little as long as they'll last a year.

 

If so, what AC/DC adapter or other thing would I need to make the voltage adjustable without/minimal heat generation? It doesn't need to be something flashy, just some way I can set it and forget it. Heat is something I'd like to avoid.

 

There seem to be different types of "G4 LED discs", but some of the pictures I find online (like this one: https://sc01.alicdn.com/kf/HTB1lRVzKFXXXXbTXpXXq6xXFXXXF/Long-Life-G4-LED-Disc-Light-Bulb.jpg) seem to include the components for a switching regulator. (namely the coil and capacitor draw attention).

 

That makes sense as LED's are current controlled, so you'd need some way to limit/control current and a linear device such as a series resistor is very inefficient, but a switching current regulator would be highly efficient.

 

Applying PWM to the input of a switching regulator won't work and would perhaps even damage the device, it needs a clean supply.

Running it at a lower voltage might vary the brightness of the led's but it is running the controller out of spec. The device will try to compensate by increasing the duty cycle, perhaps even beyond safe levels causing possible damage in the long run.

[dtaflorida]

9 minutes ago, Unimportant said:

Running it at a lower voltage might vary the brightness of the led's but it is running the controller out of spec. The device will try to compensate by increasing the duty cycle, perhaps even beyond safe levels causing possible damage in the long run.

Yeah I see a capacitor and coil on mine. It's just like your photo. This is it:

https://www.amazon.com/HERO-LED-SG4-12T-WW-Halogen-Replacement-Dimmable/dp/B00QE2TUDQ

 

So applying 18v or 24v won't make this any brighter than it is at 12v? My goal was not to provide it less voltage, I was thinking I could control brightness with by ranging the voltage from 12v to 24v since the bulb says input: 12v-30v.

 

[dany_boy]

1 hour ago, dtaflorida said:

Yeah I see a capacitor and coil on mine. It's just like your photo. This is it:

https://www.amazon.com/HERO-LED-SG4-12T-WW-Halogen-Replacement-Dimmable/dp/B00QE2TUDQ

 

So applying 18v or 24v won't make this any brighter than it is at 12v? My goal was not to provide it less voltage, I was thinking I could control brightness with by ranging the voltage from 12v to 24v since the bulb says input: 12v-30v.

 

The Vreg in the bulb will do its work and provide clean power to the LEDs as long as you provide 12-30v. Anything between that voltage range will result in the same brightness. Depending on the regulator type, higher voltage will mean more heat dissipation by the regulator. Anything higher than the specified max voltage will most likely release the magic smoke. However, if you lower the voltage below 12v, the regulator is forced to provide a lower voltage to the LEDs.

[dtaflorida]

Ok, well that sucks. Thanks everybody!