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Thread: Direct Drive?

  1. #1

    Default Direct Drive?

    Can someone explain to me what a direct drive LED light is and what is the difference with a non-direct drive?

    Sorry I'm new at this I searched but still don't understand.

    I posted asking about the new Surefire KX4, what kind of drive is that.

    I also have a Malkoff M61, what type of drive is that one.

    Which is best?

  2. #2
    Flashaholic* AnAppleSnail's Avatar
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    Default Re: Direct Drive?

    Quote Originally Posted by 5Sport View Post
    Can someone explain to me what a direct drive LED light is and what is the difference with a non-direct drive?

    Sorry I'm new at this I searched but still don't understand.

    I posted asking about the new Surefire KX4, what kind of drive is that.

    I also have a Malkoff M61, what type of drive is that one.

    Which is best?
    Search is my friend.

    "Explain Direct Drive. Batteries wired to the light emitter with nothing limiting current or voltage. Non-direct drive either regulates or limits this current flow. It can be a resistor or complex electronics. The electronics can provide "direct drive" a certain percentage of the time to limit current (90% on 10% off gives 90% power), or use more complicated things to let out a fixed voltage or current.

    surefire kx4 regulation. Probably regulated.

    The malkoff is too. Most high-end LED products are regulated. Why?

    An LED has an interesting relationship to voltage and current. If I put 3.2v onto a Cree XP-G, it will allow a certain amount of current through it (about 350 mA), just like any electronic part that we aren't burning with power. A VERY SMALL increase in voltage greatly changes the current. Also, individual LEDs vary in their forward voltage. if I give that cree XP-G 4.0v, it will be taking over 1.5 amps, and at 5v it will burn out soon. The narrow voltage range that gives light without toasting the LED hugely limits battery options.

    Regulation electronics extend this voltage range. A resistor is one way - at high current the voltage drop in the resistor is greater. But that burns a lot of heat in the resistor and is very dependent on the forward voltage of the LED.

    LEDs are sensitive to current, so most regulated LED lights (like the ones you asked about) use constant-current regulation. This is achieved with Buck or Boost drivers, and in Constant-current or PWM regulation. Start here
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  3. #3

    Default Re: Direct Drive?

    Thanks for the reply, and I did search. Of course, to be honest with you, you lost me in your explanation. I am not savvy about most of this elestronic speak.

    In both of those lights, does that mean at a certain point, will the light just cut off, or just keep getting dimmer until it doesn't work.

    Thanks

  4. #4
    Flashaholic* Henk_Lu's Avatar
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    Default Re: Direct Drive?

    I thought I have understood the term "direct drive", but Nailbender's offers made me wonder again...

    You get, for example, a 3-mode driver REGULATED with 100, 400 and 2.800 mAh and the same 3-mode driver DIRECT DRIVE with 100, 400 and 2.800 mAh.

    Can somebody explain the difference of these drivers? If the direct drive was 100, 400 mAh and then the high mode in direct drive, I'd understand. Perhaps it simply means, that the regulated driver switches to 400mAh if there's not enough juice for 2.800mAh anymore, while the direct drive keeps the high mode and forwards the LED what's available? Hm, perhaps I just answered my question?
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    Default Re: Direct Drive?

    In a nutshell, a light that's direct drive will startat the brightest it can get, then slowly dim until the voltage of the battery is too low to power it and it turns off.

    The opposite is a regulated light where the flashlight emits the same amount of light for the entire batteries charge, then simply shuts off (no dimming) when the battery is dead.
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  6. #6

    Default Re: Direct Drive?

    dd is a simple circuit, led\bulb switch and battery, nothing more,
    regulated\non dd drive is when there is a extra part regulator\driver, between the switch and the bulb, the regulator sends specific amount of electricity to the bulb, no matter how many batteries are there.

    some regulators will cut off when battery can no longer supply amount of power it needs, some drivers will turn off regulation, and just work as dd so the light will gradually dim

  7. #7
    *Flashaholic* wquiles's Avatar
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    Default Re: Direct Drive?

    Quote Originally Posted by 5Sport View Post
    Can someone explain to me what a direct drive LED light is and what is the difference with a non-direct drive?

    Sorry I'm new at this I searched but still don't understand.

    I posted asking about the new Surefire KX4, what kind of drive is that.

    I also have a Malkoff M61, what type of drive is that one.

    Which is best?
    DD (Direct drive) is the most efficient (all power goes to the LED, nothing lost to regulation), but a regulated LED is safer to the LED, and keeps the output constant while the battery drains. I did an intro post some time back that talks about LED's, regulation, and DD (Direct Drive) - here is the link in case it can help cover some of the questions you have:
    http://www.candlepowerforums.com/vb/...02#post3240702

    Will
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  8. #8
    Flashaholic* AnAppleSnail's Avatar
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    Default Re: Direct Drive?

    Quote Originally Posted by 5Sport View Post
    Thanks for the reply, and I did search. Of course, to be honest with you, you lost me in your explanation. I am not savvy about most of this elestronic speak.

    In both of those lights, does that mean at a certain point, will the light just cut off, or just keep getting dimmer until it doesn't work.

    Thanks
    Direct drive has the battery running the LED with no limits on it. This can cause some problems though: What if the batteries aren't giving power at the right voltage? A slight voltage change represents a large change in current for the LED. As the batteries weaken, so does the light. And if you get different batteries the LED might burn out. To keep the brightness constant through the battery life, AND to keep from roasting LEDs, people use electronics to mess with the input power.

    If I stand by a lightswitch and flip it quickly off-on-off-on-off-on, you won't get as much light as if it were on constantly. If I dwell on the "off" for longer, there's less light, and if I leave the switch 'on' longer you get more light. And if I can switch it quickly enough you won't notice the blinking. That's "Pulse-width modulation," where electronics quickly connect and disconnect the LED to limit the current going through. PWM is ideally either 100% power or 0% power, and will be 'On' for a given percentage of the time.

    This sort of light is still battery-dependent, but it gives you control over LED brightness. If you put higher-voltage batteries in one then all the settings will be brighter. It's also possible to damage your LED this way, BUT a temperature sensor can step in and cut down on the power going into the LED if it registers a too-high temperature.

    Other light controls:

    You can add a resistor to this to limit the current going through the LED. The voltage of the battery will equal the voltage of the LED plus the voltage of the resistor, at that particular current. Some lights switch from direct-drive to resistor-limited power to get two modes. You could do a lot of different modes with resistors, but it can be inefficient. If you're burning tons of power in the resistor you'll have a nice heater and a short-lived light battery.

    Constant-current control uses more complex electronics. I have to think of it as a magic black box that does what it needs to put a specific amount of current into an LED. There are three types of constant-current drivers: Boost, buck, and buck/boost. A boost driver boosts voltage. A buck driver lowers it. And a buck/boost driver is more versatile. Some lights use these circuits with PWM to make different output levels, others just change the output constant current.

    Boost: A boost driver will take low-voltage input and make higher-voltage output. That's how the Quark MiNi can run a 3.2v LED with a 1.5v battery. To get the higher-voltage power you want, you have to draw more current from the battery. Doubling the voltage would require about twice the current from the battery.

    Buck: A buck driver will take higher-voltage input and make lower-voltage output. 2-li-ion LED lights use this - their batteries start at 8.4v, plenty to cook an LED. With (some components and stuff), a buck driver outputs lower-voltage constant-current power to the LED. This draws less current from the batteries to get the power the LED needs.

    Summary: Direct drive is very simple, but requires good planning for the batteries. Picking the wrong batteries will either give you less light or destroy the LEDs you connect. These are generally one-speed lights.

    Indirect drive: Resistor, Pulse Width Modulation (PWM), constant-current (With buck, boost, and buck/boost).

    Indirect drive is more complex but gives more options. You can have different brightness settings to extend battery life, you can use different battery voltages than exactly-the-right one, and you can guarantee a particular level of output. ONLY a boost driver will give you high LED output from 2AA batteries.
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  9. #9
    *Flashaholic* wquiles's Avatar
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    Default Re: Direct Drive?

    Quote Originally Posted by AnAppleSnail View Post
    Direct drive has the battery running the LED with no limits on it. This can cause some problems though: What if the batteries aren't giving power at the right voltage? A slight voltage change represents a large change in current for the LED. As the batteries weaken, so does the light. And if you get different batteries the LED might burn out. To keep the brightness constant through the battery life, AND to keep from roasting LEDs, people use electronics to mess with the input power.

    If I stand by a lightswitch and flip it quickly off-on-off-on-off-on, you won't get as much light as if it were on constantly. If I dwell on the "off" for longer, there's less light, and if I leave the switch 'on' longer you get more light. And if I can switch it quickly enough you won't notice the blinking. That's "Pulse-width modulation," where electronics quickly connect and disconnect the LED to limit the current going through. PWM is ideally either 100% power or 0% power, and will be 'On' for a given percentage of the time.

    This sort of light is still battery-dependent, but it gives you control over LED brightness. If you put higher-voltage batteries in one then all the settings will be brighter. It's also possible to damage your LED this way, BUT a temperature sensor can step in and cut down on the power going into the LED if it registers a too-high temperature.

    Other light controls:

    You can add a resistor to this to limit the current going through the LED. The voltage of the battery will equal the voltage of the LED plus the voltage of the resistor, at that particular current. Some lights switch from direct-drive to resistor-limited power to get two modes. You could do a lot of different modes with resistors, but it can be inefficient. If you're burning tons of power in the resistor you'll have a nice heater and a short-lived light battery.

    Constant-current control uses more complex electronics. I have to think of it as a magic black box that does what it needs to put a specific amount of current into an LED. There are three types of constant-current drivers: Boost, buck, and buck/boost. A boost driver boosts voltage. A buck driver lowers it. And a buck/boost driver is more versatile. Some lights use these circuits with PWM to make different output levels, others just change the output constant current.

    Boost: A boost driver will take low-voltage input and make higher-voltage output. That's how the Quark MiNi can run a 3.2v LED with a 1.5v battery. To get the higher-voltage power you want, you have to draw more current from the battery. Doubling the voltage would require about twice the current from the battery.

    Buck: A buck driver will take higher-voltage input and make lower-voltage output. 2-li-ion LED lights use this - their batteries start at 8.4v, plenty to cook an LED. With (some components and stuff), a buck driver outputs lower-voltage constant-current power to the LED. This draws less current from the batteries to get the power the LED needs.

    Summary: Direct drive is very simple, but requires good planning for the batteries. Picking the wrong batteries will either give you less light or destroy the LEDs you connect. These are generally one-speed lights.

    Indirect drive: Resistor, Pulse Width Modulation (PWM), constant-current (With buck, boost, and buck/boost).

    Indirect drive is more complex but gives more options. You can have different brightness settings to extend battery life, you can use different battery voltages than exactly-the-right one, and you can guarantee a particular level of output. ONLY a boost driver will give you high LED output from 2AA batteries.
    A very good summary, and your description on Buck, Boost, etc. is right on the money, but the terminology is not what I would call consistent with what we use in the forums at least for the last 6 years that I have been participating in the forums.

    Maybe it is just a matter of semantics, but I would suggest that we use the same terminology that most/all of us use. The correct terminology to use is "regulated" or "not regulated", and note that "not regulated" is often used interchangeably with "DD (Direct Drive)".

    - Regulated has two possible types: Current Regulated (also known as constant current) and Voltage regulated (also known as constant voltage).

    - For LED's only current regulated guarantees that the LED will get the exact current it needs as the input voltage changes (cells get depleted), and regardless of the vf of the LED. So the same current regulated LED driver will deliver (for example) 1500mA to LED A with a vf of 3.2 volts and will also deliver 1500mA to LED B with a vf of 3.9 volts.

    - Voltage regulated mostly applicable for incandescent bulbs, which need the voltage to stay constant as the cells are depleted. Voltage regulation does not account for variations/changes in the vf and/or LED die temperature, so the current can not be guaranteed to stay constant. Some folks compensate this behavior with the use of a thermistor, but if all all possible, the use of a true constant current regulator is the best option.


    Given this:
    - LED connected directly to the cell/cells, is direct drive (DD).

    - Using a resistor in-line with the LED "is" still direct drive - the resistor regulates nothing. The resistor simply limits the flow of current, but if the cell/cells have a higher voltage or if the vf of the LED is smaller than average/typical, you can still over drive the LED and kill it. If in the example above we have a LED B with vf of 3.8 and we pick a resistor to provide a max current of about (for example, per LED's data sheet) 1000mA, and then you replace LED A (same company, same type, same color, etc., just a different vf) with vf of 3.2 volts, you "will" exceed the 1000mA max current.

    PWD is tricky. Having PWM does not always means that the driver/circuit is regulated. PWM might be used for dimming, but that is all we can know for sure, unless you look deeper and/or perform some tests on your own.

    - Having "plain" PWM is always direct drive. In fact most/all of the "regulated" lights coming from Asia are "not" regulating anything. They simply use PWM to give you various levels by dimming the LED. A few might add a resistor to try to account for variations between CR123 cells and LiIons, but again, there is no regulation taking place.

    A good example of a high quality PWD-only, Direct Drive circuit is the D2Flex. George (the designer) will clearly tell you in his web site. There is no voltage nor current regulation happening here. Instead of a "fixed" resistor, the PWM allows you a "variable resistor" so that you can dim the LED. However, just like in the case with the resistor, there is NOTHING to guarantee that the LED will see a specific current. Same as above with a single resistor - there is nothing to guarantee that the current will be lower/higher as the vf of the LED changes.

    - True regulated current drivers can be of a fixed level (like say, 500mA, 1000mA, or 2.6Amps, etc.), or could offer various levels, but even if offering various levels, the max. current will not be exceeded if there is input voltage variation (within the limits of the driver), and the max. current will not change depending on the vf of the LED. Most of the current regulated LED drivers that we have access here in the forums accomplish the various levels by use of PWM. So in this case PWM is just doing the dimming, while the current regulated core guarantees that the LED will not get more than the design/set value. Perfect example, the Flex drivers from TaskLED, like the hipFlex.


    Will
    Last edited by wquiles; 07-23-2010 at 11:44 AM.
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    Default Re: Direct Drive?

    Quote Originally Posted by wquiles View Post
    A very good summary, and your description on Buck, Boost, etc. is right on the money, but the terminology is not what I would call consistent with what we use in the forums at least for the last 6 years that I have been participating in the forums.
    I have also tried to describe the different type of drive here: http://candlepowerforums.com/vb/showthread.php?t=247543 and I believe that it is coincident with your explanation.
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  11. #11
    *Flashaholic* wquiles's Avatar
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    Default Re: Direct Drive?

    Quote Originally Posted by HKJ View Post
    I have also tried to describe the different type of drive here: http://candlepowerforums.com/vb/showthread.php?t=247543 and I believe that it is coincident with your explanation.
    Yup, and not only that, but that is a very good post, with lots of great information, graphs, etc.. Very nicely done
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