We use LED construction lights for illuminating a photo or video set. As espected the lights flicker with the mains frequency. While in some cases this can be compensated with the right camerasettings it would be a lot easier if the flickering could be removed.
The lights have total of 100W at 230V/50Hz.
Osram LED worklight 2x50W
So I started out with a simple idea. A full-wave bridge rectifier with a smoothing capacitor. I had 22μF/400V capacitor and a 2W08G rectifier. The lights already flicker a lot less but the capacitor would need to be bigger of course.
A larger capacitor will result in a smoother DC, hoever that DC is still close to 325VDC which means way more power for the LEDs. Since I have no idea what, if any, electronics the lights have inside (I can not open them without likely breaking them), I do not know if thats an issue. I mean the lights have to deal with that voltage and current at the top of the sine curve, but only for a brief moment. With 325VDC I would expect the lights to get way hotter than allowed and eventually fail.
Questions:
- Are my assumptions correct so far, or can I go with this simple solution for this application?
- If I can go with 1., do I need any extra restiors to protect the rectifier and/or capacitor?
- Is there a cheap (no more than 30€) and size wise small (<25cm³) solution that would give me a somewhat stable 230VDC? (I can't find any ICs that can deal with that kind of voltage.)
Addendum 1:
- all LEDs are on when behind the rectifier, so I guess the lamps already contain a rectifier inside, just nothing to smooth the waveform
Best Answer
A POSSIBLE solution that is "easy & cheap enough" to try is to use a light dimmer unit followed by your full bridge rectifier plus filter capacitor.
Cheap dimmers usually use "phase angle control", so the waveform is truncated to a variable extent at the start of the cycle. This means that the peak voltage is usually about the same and if lightly loaded the DC will be at about the same level as before :-(.
However, as you reduce the dimmer output level you may achieve a result that is satisfactory. There re enough variables there to make it not certain, but it's probably worth trying.
Some dimmers provide high frequency PWM switching of the input AC waveform and so give a far less distorted output waveform.
They are less common and probably substantially more expensive.
A fairly 'Heath Robinson'* solution is to place a load of about half the LED light effective resistance in series with the rectifier plus LEDs - either in the AC or DC sides. This could be eg several 100 Watt incandescent light bulbs in parallel or perhaps a domestic toaster element (in or out of toaster :-) ). [Stove element, electric kettle element, ... ].
Some experiment would probably be required but the result could be effective and lowish cost if not very pretty.
A more certain but more costly method is to use a 'variac' variable output voltage transformer.
These do not distort the waveform.
It may be (or may not) that use of a 220:110V step down transformer plus bridge rectifier will be adequate. Peak voltage is then Vin x 1/2 x 1.414 ~~~= 160 VDC if well filtered. Whether your LEDs handle that well is tbd. 230:110 or similar transformers are often available at relatively low cost for their power ratings.
Unlikely but possible: A transfomer with tappings or secondary windings that give you about 230V:160VAC will give you about 230 VDC when peak rectified.
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*If you don't know about Heath Robinson, it's worth making his acquaintance :-)