In a failure scenario...... Otherwise, there wouldn't. The LEDs would combined with the chip would have enough forward voltage drop to reduce that.
GS8208 12V pixel strings - A wildcard third option for the 5V vs 12V WS2811 question?
- Thread starter ryanschristmaslights
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If the chip output pin ever shorted to 0V, the resistor would pop in an instant. Not much chance of a fire.
TerryK
Retired Elf
Skymaster mentioned (Post 28) if the IC short-circuited. Although, with the internal 7805 both the logic part of the IC and the regulator would need to go. The IC logic only, I would think it would depend if the regulator would current limit and if so at what point.
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Since we're speculating, I'll throw my guess in too...
The resistor is there for current limiting during normal operation. The output circuit for each of the pins looks to be FETs which I presume they are simply turning on / off, rather than using them in any sort of linear region.
Given the LEDs would have a certain forward voltage drop, the resistor will limit the 'on' current. As the chip has an internal regulator / voltage reference, it could then also be sampling the voltage at VDH, effectively measuring the voltage drop on the resistor and therefore the current through the LEDs. It may then be using that value to adjust the 'on' time for the FETs, allowing it to regulate the average current.
The resistor is there for current limiting during normal operation. The output circuit for each of the pins looks to be FETs which I presume they are simply turning on / off, rather than using them in any sort of linear region.
Given the LEDs would have a certain forward voltage drop, the resistor will limit the 'on' current. As the chip has an internal regulator / voltage reference, it could then also be sampling the voltage at VDH, effectively measuring the voltage drop on the resistor and therefore the current through the LEDs. It may then be using that value to adjust the 'on' time for the FETs, allowing it to regulate the average current.
I have some here that I never got to testing. I will however claim to have some involvement with Ryan's testing and test results as I was talking to him prior to him buying them and was working with him on the test procedure for him to get some results. It's partially through our conversations that this thread got bulked up with some information.
I'm actually still interested in selling GS8208 strings as they have a lot of advantages that other don't have. They would be the only 12V nodes that I'd consider unless there was a similar Worldsemi or other brand that came on the market.
"The greatest trick the Devil ever pulled was convincing the world that 12V WS2811 nodes were a good thing."
TerryK
Retired Elf
Well, I do not think so but that's just my opinion. I do not have the numbers available presently but the WS2811 5 Volt pixels I tested worked rather well down to about 4 Volt. Around there the pixels were starting to dim enough for me to notice. I was working with white, did not see any color shift yet at that voltage.
The voltage sensitivity around flickering affects 12v pixels rather than 5v.
5v pixels continue to regenerate the data stream well below their effective usefulness in creating colours.
Only when you get under the Vf of the blue and green leds do you see colour changes and this occurs around 3.3v typically.
In this test the end of the string was around 3.8v measured and still looked normal with a small measured drop due to the constant current setup.
The voltage drop and having to power inject is actually a good thing. The wire used in pixels is tiny and is generally not the specification that they say they are. When you drop up to 8V using 12V pixels you are massively exceeding the safe working current for the wire. In general the wires used are only suitable to directly power about 50 pixels. It's actually on my to do list to do full video on the issues with powering WS2811 pixels from 12V. I spoke a bit about it at the Sydney mini.
The biggest advantage of the 12V GS8208 vs WS2811 is that the current for the GS8208 has the 3 colours in series rather than in parallel. This means that there is a maximum current of about 18.5mA per pixel rather than 55mA. Having 1/3 of the current means that there is 1/3 of the voltage drop. These pixels can't handle the same 8V voltage drop that WS2811 pixels can but they are much better suited to the wire size that pixels come with.
There are many people using a full 5V pixel display and it's just a matter of taking care of the voltage. Connect the beginning and ends of the props together, add some more power injection and potentially use some heavier wires.
- Thread starter
- #42
I get 2.6-2.7Ω (ohms) for 2x 50 pixel strings connected together. This is with the V+ and gnd of pixel 1's injection pigtail twisted together and the measurement taken between V+ and gnd at the opposite end (after 100th pixel).
As far as voltage on 100% white, what starts at
11.91V drops down to 11.36V at the end of the 100th pixel (2x strings of 50).Reselling GS8208 strings locally, you say - well that cat is out of the bag now!
Should be great having a local source of GS8208 for those who would like some.While I bought bullet strings from Shiji Lighting, a square node version is advertised on Alibaba for US$0.25-0.30 per pixel from another supplier, Kingtar Technology (1, 2).
MichaelF5
Apprentice elf
A regulator will actually lose you headroom. Most cheap regulators will drop a couple of volts across them. So adding a regulator to a 12V pixel will only give you an output of about 9.5V of working voltage.
The regulator is 1 of the 2 options to run WS2811 pixel IC's as they are actually 5V devices. The regulator can drop the 12V down to 5V or a series resistor can sorta drop the voltage. The series resistor is actually the specified method in the data sheet. The 5V is fine as the leds have a voltage drop of about 2.2-2.6V and the balance of that voltage is dropped within the pixel IC as part of a constant current circuit that converts the excess voltage to heat. The 12V pixels, either regulator or resistor, will work down to maybe as low as 4V input but will get very flaky as the 5V voltage can't be/isn't maintained.
MichaelF5
Apprentice elf
what are the options? from what I could see of the spec sheet you guys found of the one Ray was using was good for up to a 30v input, so a 2v drop would get you quite some distance and still give you more than 10v output?
from what i could make of the data sheet, the higher the output voltage, the higher the input could be for the same device
Edit this was one discussed being used by Ray https://pdf1.alldatasheet.com/datasheet-pdf/view/22687/STMICROELECTRONICS/78L05.html
for 12-15v output up to 35v input... sweeeeeeeeet
from what i could make of the data sheet, the higher the output voltage, the higher the input could be for the same device
Edit this was one discussed being used by Ray https://pdf1.alldatasheet.com/datasheet-pdf/view/22687/STMICROELECTRONICS/78L05.html
for 12-15v output up to 35v input... sweeeeeeeeet