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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
New information:
So it looks like the most efficient way to drive LED's from a 240V mains supply is something like this:
The inductors are 1000uH, and are 79 turns on T-225A-26 (2 1/4" OD yellow/white), resistance should be around 200 milli-ohms each, maybe less. I've used 3x330uF 100V in series to simulate ~100uF, 300V. The other capacitor is 10uF. Diodes are MUR320, although I think MUR340 may be a better option. LED's are AOT-2015. The circuit draws ~23mA from the mains. That's around five watts for 80 LED's, which is ~60mW per LED.
EDIT: The following screenshots are a comparison of using two 1000uH inductors, compared to using one 10 Ohm resistor.
This is the steady state for both cases, showing current through D1 and the LED's:
This is just current through the LED's. Current is a couple of milliamps higher with inductors. Does this mean 10% more light?
This is the transient state, where it is switched on mid-cycle. The inductor solution also performs a bit better here, although the resistor probably performs adequately, and could possibly be replaced with a lesser value one, depending on what peak current you find acceptable:
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Not yet all hell broke loose here after that then two years of total chaos. I'm only just picking up the pieces now. All the components including the inductors I wound are around here somewhere, but the 'scope was put away and hasn't come out since.
I'm catching up with paperwork at the moment, and as soon as we get some better weather I need to drop the front subframe out of the Saab, my priorities, as far as electronics goes, at the moment are getting the control box for my lathe finished,which is also waiting for warmer weather. I also have a valve amp coming together slowly. I have most of the parts, but want to use interstage transformers to reverse the phase. Looks like if I want 1:1 ratio I'll have to wind my own, which is another job I need to get in the shed to do.
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
Nice teardown video. It's good to see my drive circuit being used in commercial products, give or take a resistor. Interesting to see they've picked practically the same voltages as well.
My simple circuit with rectifier bridge, capacitor and resistor to limit the initial inrush current worked pretty well. However, in order to drive a high power led, the capacitor needs to be big (and expensive). I was thinking of using an electrolytic (of appropriate voltage) after the bridge rectifier. Do you think is going to work?
Registered Member #72
Joined: Thu Feb 09 2006, 08:29AM
Location: UK St. Albans
Posts: 1659
kimbomba wrote ...
... in order to drive a high power led, the capacitor needs to be big (and expensive). I was thinking of using an electrolytic (of appropriate voltage) after the bridge rectifier. Do you think is going to work?
No. Think about what happens once the cap is charged with DC.
This dropper technique only works well when the LED voltage is in the 50% to 75% of the supply voltage range. Only low current high voltage LEDs make sense for this configuration.
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Driving a led with mains.
