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Thread: Some Chinese designed LEDs are now using resistive series ballast

  1. #11
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    Quote Originally Posted by steve66 View Post
    Sorry, but I think your initial premise is flawed. This doesn't look at all like a simple series resistor (or even a simple linear regulator) to me.

    http://www.onsemi.com/pub/Collateral/NCL30051-D.PDF

    I believe the power that would be lost by a linear regulator would make it impossible to use a linear regulator (or series resistor) for anything over a few watts without including a heavy, bulky transformer.

    It looks to me like they have gone to extreme lengths to squeeze every drop of efficiency out of the total chip/driver/LED package.
    Well the China datasheet is stamped "CONFIDENTIAL" for some reason so I had to remake the post without using screen shots or direct link to it.

    Nah, that's not the one I linked. This is the one I referenced.
    http://www.onsemi.com/pub/Collateral/AND9041-D.PDF

    I have not come across LED lamps using linear dropper ballast until this year.

    The no name LED lamp had an internal construction like this, which was determined wholly through product tear down.



    The variable resistor dynamically changes to adjust current while flaring off energy in the package.
    This is a more generic equivalent circuit. That resistor sets the current.
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    The Greenlite 9W/LED/OMNI/D* uses some China chips SM2082D and SM2082ED, although they work on the same principle.

    The increase in line voltage causes increased voltage drop at the linear dropper LED ballast which increases thermal dissipation at the lamp which lowers LED element efficacy.

  2. #12
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    @Roger:

    I'm with Electric-Light on this one. A lot of times when you Google the part numbers of the chips on LED fixtures you get plenty of declassified PDFs that say "confidential" An example, click on the first few PDFs:


    https://www.google.com/search?source...k1.7UdoHY9Ngj8

    There are also a number of videos on You Tube where people will dismantle LED lamps, read the number off the chip and then download similar documents right off line in regards to explaining how the chip works.

    See point 3:11 showing the exact same doc:

    https://www.youtube.com/watch?v=KKd2L9Exw0M
    Last edited by mbrooke; 09-08-17 at 06:17 PM.
    What is esoteric knowledge today will be common knowledge tomorrow.

  3. #13
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    Quote Originally Posted by steve66 View Post
    Sorry, but I think your initial premise is flawed. This doesn't look at all like a simple series resistor (or even a simple linear regulator) to me.

    http://www.onsemi.com/pub/Collateral/NCL30051-D.PDF

    I believe the power that would be lost by a linear regulator would make it impossible to use a linear regulator (or series resistor) for anything over a few watts without including a heavy, bulky transformer.

    It looks to me like they have gone to extreme lengths to squeeze every drop of efficiency out of the total chip/driver/LED package.
    I am probably wrong, but I see it the same way. I don't think thats a variable resistor but rather a very fast switching variable "triac" It opens the gate for a drop in voltage and closes it when voltage spikes in an effort to modulate a near constant current. That voltage threshold determined by the resistor tacked across one leg of the chip.
    What is esoteric knowledge today will be common knowledge tomorrow.

  4. #14
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    I agree with Electric-Light's analysis of the lamp.

    120V gets rectified to give about 170V DC.

    The LEDs are arranged to have a voltage drop of about 144V.

    A _linear regulator_ is arranged to drop the difference between the rectified mains voltage and the LED forward voltage.

    This is _not_ a PWM style switching regulator because the LEDs are non-linear and if you rapidly turned them on and off the peak current would be much higher than desired. This is not like PWM dimming of a resistive load like an incandescent lamp.

    A switching regulator for LEDs require the use of energy storage such as inductors and a much more complicated circuit.

    The greater the LED voltage as a fraction of the rectified mains voltage, the greater the efficiency of the driver circuit.

    At the nominal 120V supply voltage, the driver circuit is about 86% efficient, which is probably as good as you will get with a switching regulator at this power level. You have 24V * load current dissipated as heat by the regulator and (144V * load current - light output) dissipated as head by the LEDs. Put the LEDs and the regulator on the same heat sink, and it just runs a bit warmer.

    With this circuit, the power consumption is essentially linear with supply voltage, with constant power dissipated in the LEDs string and the difference dissipated as heat by the _linear_ regulator circuit. If the supply voltage is 10% high, then the heat dissipated by the regulator circuit almost doubles. Still less than what the LEDs are dissipating, but a very significant change, and one that needs to be understood by proper testing.

    With this circuit, if the supply voltage is 10% low, the system probably stays in regulation, but you might see an increase in flicker, again something that needs to be understood with proper testing.

    Sorry for making this so long...I don't have time to edit it shorter.

    -Jon

  5. #15
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    Quote Originally Posted by Electric-Light View Post
    The variable resistor dynamically changes to adjust current while flaring off energy in the package.
    One small error in your schematic: I expect the full lamp current (60mA) is passing through the sense resistor, with the ballast chip measuring (and regulating) the voltage across the resistor.

    -Jon

  6. #16
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    170909-2043 EDT

    From post 11 there is a part number BP5131H in the circuit diagram. I can only find via Google one Chinese datasheet that is somewhat readable in English. This part number is probably a linear current regulator.

    What is a linear current regulator. Fundamentally it is an adjustable resistor that is continuously adjusted by control circuitry that senses the voltage drop across a current sensing resistor that is in series with the current thru the adjustable resistor.

    In the shown circuit this current sensor is 8.55 ohms. The stated controlled output current is 0.06 A. At 0.06 A the voltage drop is 0.51 V. In the datasheet there appears to be an 0.6 V value given for this control point. These seem to correlate.

    The datasheet specifies 1.25 W maximum dissipation, and a maximum junction temperature of 155 C. Maximum current is listed at 80 mA (0.08 A).

    In a series pass regulator, whether voltage or current, or in between, the power dissipated in the controlling element (the adjustable resistor) is the voltage drop across the regulator times the current thru the regulator.

    First question is can I physically build the circuit (mechanical mounting) to dissipate 1.25 W at a realistic ambient temperature and stay below a 155 C junction temperature? It is a very small chip and I doubt it for what are probable chip case temperatures. I would never design for a 155 C junction temperature if I want long term reliability.

    The circuit is moderately below the the maximum current rating and thus this is not a major concern.

    The next problem is the needed power dissipation. Once the LEDs stabilize, then at constant current their power dissipation is constant. This power dissipation we are not concerned with except as it increases the ambient temperature of the regulator chip.

    If we assume that worst case load on the regulator is 144 V at 0.06 A (meaning minimum voltage and maximum current), and maximum voltage input to the regulator is 120/0.707 = 170, then the maximum power dissipation in the regulator is (170-144)*0.06 = 1.56 W. To start with this is above the maximum rating, and for realistic heat sinking conditions and maximum junction temperature you would not wnat to even operate at a 1.25 W level.

    It gets even worse when you make a realistic assumption that a bulb might work at 125 to 130 V. At 130 V the series pass dissipation is ( (130/0.707) - 144 ) * 0.06 = 2.4 W.

    .

  7. #17
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    steve66's comments based on what was provided is correct. I pasted the wrong link.

    This is the linear ballast type LED driver I was talking about the whole time.
    On Semiconductor Design Note – 05079/D

    Something you will see in one of the tables is that their example circuit exhibits 9% efficacy loss when you go from the lower end of bandwidth to upper end of ANSI tolerance. 114 vs 126v. The increase in power is increase in ballast power dissipation which increases temperature. This means users closer to substation would chronically experience higher power consumption from these lamps as well as accelerated wear.

    Someone evaluated the same model Greenlite integral-ballast LED lamp in this video.
    https://youtu.be/zJWssuCGkC8?t=360s

    the unit he evaluated has a switch mode converter ballast that drives two parallel strings of 5 three chip LED elements in series.

    My sample drives 16 three-chip LED elements in series through a linear drop out ballast. They both have the exact same model number and there is no way to tell them apart. I don't believe the criteria for Energy Star considered the potential of cost engineers coming back around to chip away realistic durability and performance from the product design and leaving behind the absolute minimum to meet the required by specifications. When you go to Energy Star website, there are multiple Greenlite 9W 800 lm LEDs but do not allow positive identification of these samples. Two different date codes of these lamps were energized simultaneously and they have a dramatically different dimming curve which means they dim totally differently alongside on the same dimmer because they have different integral ballasts.

    I think it's a concern that a product that has gone through a cost reduction engineering change so drastic that the there's nothing in common between the two products and they're still allowed to bear the Energy Star logo under the same model number. The version he reviewed used a 130C capacitor, the version I evaluated used a 105C capacitor. Presumably both of these products meet the specs under lab conditions but they provide different realistic performance despite the same model number. You can not tell the two apart without breaking them open. What prompted an extensive evaluation was the fact the several samples of the new version gave off burning plastic smell and case temperature of 230*F.

    ANSI allows +/- 5% from nominal and I think its reasonable to expect the same performance within the parameter and currently, Energy Star standard allows any amount of flicker only for LED lamps as long as it is happening at 120Hz or above and there are too many LED products out there that take this literally and omit smoothing capacitor entirely.

    With linear ballast, when line voltage goes up:
    LED current is held constant. (constant ballast factor)
    Power consumption and dissipation goes up (Lowering BEF, increasing Tc temp)
    Indirectly, the lamp temperature goes up which lowers Vf (further reduction in efficacy, as well as life)

    Several issues here:

    Energy Star does not limit flicker in a meaningful way. It mandates HF operation for CFL but holds LEDs to the lesser standard of direct AC line flicker which gives nearly the same flicker as a 60Hz driven red neon lamp.

    Products are allowed go under a total gut change and bear Energy Star logo and recycle model # without letting consumers know of difference.

    No limit on performance or durability deviation when operated above or below nominal voltage but within the ANSI tolerance.



    Last edited by Electric-Light; 09-11-17 at 06:54 PM.

  8. #18
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    Quote Originally Posted by gar View Post
    170909-2043 EDT

    From post 11 there is a part number BP5131H in the circuit diagram. I can only find via Google one Chinese datasheet that is somewhat readable in English. This part number is probably a linear current regulator.

    What is a linear current regulator. Fundamentally it is an adjustable resistor that is continuously adjusted by control circuitry that senses the voltage drop across a current sensing resistor that is in series with the current thru the adjustable resistor.

    In the shown circuit this current sensor is 8.55 ohms. The stated controlled output current is 0.06 A. At 0.06 A the voltage drop is 0.51 V. In the datasheet there appears to be an 0.6 V value given for this control point. These seem to correlate.

    The datasheet specifies 1.25 W maximum dissipation, and a maximum junction temperature of 155 C. Maximum current is listed at 80 mA (0.08 A).

    In a series pass regulator, whether voltage or current, or in between, the power dissipated in the controlling element (the adjustable resistor) is the voltage drop across the regulator times the current thru the regulator.

    First question is can I physically build the circuit (mechanical mounting) to dissipate 1.25 W at a realistic ambient temperature and stay below a 155 C junction temperature? It is a very small chip and I doubt it for what are probable chip case temperatures. I would never design for a 155 C junction temperature if I want long term reliability.

    The circuit is moderately below the the maximum current rating and thus this is not a major concern.

    The next problem is the needed power dissipation. Once the LEDs stabilize, then at constant current their power dissipation is constant. This power dissipation we are not concerned with except as it increases the ambient temperature of the regulator chip.

    If we assume that worst case load on the regulator is 144 V at 0.06 A (meaning minimum voltage and maximum current), and maximum voltage input to the regulator is 120/0.707 = 170, then the maximum power dissipation in the regulator is (170-144)*0.06 = 1.56 W. To start with this is above the maximum rating, and for realistic heat sinking conditions and maximum junction temperature you would not wnat to even operate at a 1.25 W level.

    It gets even worse when you make a realistic assumption that a bulb might work at 125 to 130 V. At 130 V the series pass dissipation is ( (130/0.707) - 144 ) * 0.06 = 2.4 W.

    .
    Ok- I guess I was mistaken then the whole time. Then again I've never really researched these chips in depth outside of translating Chinese which works out poorly in general let alone STEM concepts. Resistor it is instead of dimmer.

    But- I am not saying any of you guys are wrong- but wouldn't a 7 watt poses a chip that gives off 3.5 watts of heat? I can't picture such a tiny chip dissipating that much heat into the cap of the lamp, that is unless its not dissipating that level?
    What is esoteric knowledge today will be common knowledge tomorrow.

  9. #19
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    170912-2449 EDT

    Electric-Light:

    It looks like you have provided some misleading information.

    In post 11 you showed a circuit that could imply a true linear regulator, but the capacitor implies an RC time constant of possibly 2.5 milliseconds.

    You also provided a reference to a discussion on a regulator that was possibly not the BP5131H of post 11.

    Then in post 17 you reference an ON datasheet that does not map to the device in your circuit of post 11. The ON chip and circuit appear to be a form of pulse width modulation, far lower power dissipation than a linear circuit.

    In your post 17 photograph it appears that there is a larger power device, possibly an FET, and not just a single chip regulator.

    Do some circuit tracing and provide an accurate circuit diagram. Also use a scope to analyze circuit operation.

    .

  10. #20
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    Quote Originally Posted by gar View Post
    170912-2449 EDT

    Electric-Light:

    It looks like you have provided some misleading information.

    In post 11 you showed a circuit that could imply a true linear regulator, but the capacitor implies an RC time constant of possibly 2.5 milliseconds.

    You also provided a reference to a discussion on a regulator that was possibly not the BP5131H of post 11.

    Then in post 17 you reference an ON datasheet that does not map to the device in your circuit of post 11. The ON chip and circuit appear to be a form of pulse width modulation, far lower power dissipation than a linear circuit.

    In your post 17 photograph it appears that there is a larger power device, possibly an FET, and not just a single chip regulator.

    Do some circuit tracing and provide an accurate circuit diagram. Also use a scope to analyze circuit operation.

    .
    The schematic with BP5131H is some no name lamp, which uses a 10.6uF parallel capacitor.

    I provided the ON-SEMI page just for information. It does a much better job of explaining things than the sheets available for the Chinese chips relevant to the two products. The demo circuits they used for the graphs choose not to use a smoothing capacitor at all and voltage drops all the way to zero each half cycle. Remember that the load is a long string of LEDs. The PWM like effect you're seeing is from LEDs themselves commutating. The flat top is created by the linear regulator adjusting to flare off the top part of each half cycle. And it drops again when each half cycle goes below the on-state for LED stack.

    The Greenlite9W/LED/OMNI/D* pictured uses
    SM2082ED (IC looking thing)
    SM2082D (3 terminal device)
    This lamp used RTV and adhesive very liberally and it didn't yield easily and got quite banged up in the process.

    The 8 pin (really 6 pin + 2 unused pins) appears to have two devices in one one package and I believe the purpose is help with diimmer compatibility to keep conducting even when LE Diodes have not reached Vf. I couldn't find the English version so I have no idea what they're saying, but the Chinese version shows formulas that prove it's a linear dropper. The 2082D is a a single channel linear driver.

    Anyways for the purpose of relevance to this forum, the linear drop out topology accommodates line voltage regulation by flaring off excess voltage as a ballast loss. It's common for utility to aim for the top of the allowance so they make sure end the furthest point still gets 114v incoming.

    The behavior in response to sag or swell depends on where the balance point is tuned for. The unique thing is that raising the line voltage does not increase the current. It just raises the ballast's share of voltage compared to LEDs, so the ballast factor stays the same while BEF goes down.
    Last edited by Electric-Light; 09-12-17 at 06:33 AM.

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