flicker-free LED driver for video - Page 1
Forum section: electronics / projects

author: Johannsen
author_rank: Regular Contributor
timestamp: December 07, 2020, 12:25:29 pm
content: Hi,i want to build a video light and tried usual led drivers which use pwm but failed as they were flickering.So I was thinking about a constant current approach controlled with i2c. Do you think that would work?Available infos:- 9 V (IF = 800 mA)-datasheethttps://www.cree.com/led-components/media/documents/ds-CMA1306.pdf-12V car battery-I2C control

author: NiHaoMike
author_rank: Super Contributor
timestamp: December 07, 2020, 02:00:14 pm
content: Try synchronizing the PWM to the camera. If your camera doesn't have a genlock output, it's often possible to make one by connecting a HDMI to VGA adapter to the HDMI output and using the VSYNC output. Play around with the delay and find out what works best.

author: Johannsen
author_rank: Regular Contributor
timestamp: December 08, 2020, 12:37:48 am
content: Hi, thanks for your comment. That sounds like a professional hint but some of my smaller cameras eg gopros would need an additional adapter and it gets to complicated I guess.I received today a LED driver PCA9624 which uses 97kHz fixed pwm and gave it a try..and actually I can't notice any flickering at 240fps. I tried different brightnesses and there's hope it'll workOne issue however is that this IC has a max current of 100mA and I need arround 900mA.So I guess an option would be to add a MOSFET driver?IRF4905PbFSI7157DP-T1-GE3FDB9506L-F085Otherwise there is another version of this LED driver named PCA9633 where the output could be changed for both type of mosfets p or nQuoteI have no idea how to properly use an mosfet in a pwm circuit. While searching I found an AN from TIOn page 28 is an example for an n-typehttps://www.ti.com/lit/ml/slua618a/slua618a.pdfCould this be a solution and how do I calculate and choose the right componets, capacitors, inductors mentioned?

author: sam[PS]
author_rank: Contributor
timestamp: December 20, 2020, 08:42:42 pm
content: For really 0 risk of flickering you may want to go linear. The cuddos is efficiency will be much lesser than with switch mode solution, be prepared for some serious heat dissipation but at 800mA/9V we are talking about around 10W dissipation assuming 50% efficiency, so should be manageable.Good old LM317 makes good and simple constant curent source as long as you don't need over voltage protection. You should not need it anyway as your power supply is close enough to max voltage. It's possible to add it if needed at the cost of some more analog complexity but nothing extreme here I would try to use just couple resistor and a transistor to short circuit the control resistor. The curent is controlled by a resistor so if your ok using just a pot as control it's all good just be aware it must be able to support as much curent as you output. If you want digital control i've seen some old application note using binary step resistor and transistors to bypass each but all those transistors and resistor still need to be able to pass full output curent. So for higher current better go for a constant curent source using an opamp and a power darlington. Something like thishttps://www.researchgate.net/profile/Mathias_Weierganz/publication/45899961/figure/fig4/AS:667822640353308@1536232733977/Circuit-diagram-of-the-constant-current-source.pngcould work pretty well and it is commanded by a voltage on V+ so you could adapt it with any cheap I2C DAC if I2C control is what you need.Just my 2cts...