Fixing a crap Chinese video light

I dunno what the Chinese engineers have been smoking, but the design of this FalconEyes DV-216VC video light is outright ridiculous. The reason I opened it up was that the control of the thing was utterly crap. What they should have done: two controls, one for brightness and one for color temperature. What they actually did: brightness for each LED array. Not only that, the onset of the illumination is sudden and starts at a high level, about 70-80%. Then the remainder of the turn of the control it goes to full. Completely useless. The engineer in me said: I can do better than this crap.

Out with my Phillips screwdriver. Reverse engineering an existing design is never easy. Fortunately the Chinese engineers printed the component values on the board, so it got a bit easier:

OK, the drawing shows a bog-standard TL494 PWM controller. This chip is used primarily in ATX computer power supplies and it works very well. The drawback of this chip is the huge offset voltage. To cope with this, the Chinese used a plethora of extra components. Which are utterly useless and can be tossed. In the end I removed all four adjustable resistors (pots), changed some values and generally simplified the design. Even so, I couldn't fix the offset voltage but as this matters only at low intensities I left it. The main change I made is the common brightness and the color temperature. As pointed out, this doesn't work at low intensities.

RV5 controls brightness, RV6 the color temperature. I deliberately set the yellowish LEDs a bit lower because I want to stay at the cool side. I also changed the current sense resistors so the offset voltage became a bit less of an issue. Finally I removed the resistors R8, R21, R26 and R27 as well as all variable resistors (RV1-4). The second error amp in the TL494 is not used anymore but I didn't want to disconnect it because it's too much hassle.

The result: I now have a video light that works very well. Nice battery life, pretty good brightness. Diffusion of the light is a bit problematic as each LED projects its image onto the illuminated surface. Verdict: bad buy. Should have gotten my money back. There are much better lights available. A good friend of mine has a light by LEDGo which uses a diffuser with side illumination and a much better color temperature control, even compared with my improved FalconEyes piece of Chinese shit. But it was great fun redesigning and fixing the thing. Both of'em. The Analog Electronics Engineer in me rejoiced!


© Zappy TV 2016