Driver question

[texas cop]

I found this today. http://intl-outdoor.com/ld2c-3a-12-cell-circuit-board-p-732.html Question is I want to use it in a tight space to run an MT-G2, will it provide the proper voltage along with the current off of 2 cells? I understand only a little about drivers, along with the regulated current they provide how do they detect the proper voltage to push?

 

[hiuintahs]

Good question. What is confusing to me is that it looks like there are 2 versions...........a single sell (operates from 3.0 to 4.5v) or a 2-cell that operates from 5.8 to 8.4v. If the regulator circuit is designed to operate all the way up to 8.4v, then any voltage from the Vled up to 8.4v would be stepped down. The question comes as to how does it know to go into low output flashing mode............at either the 3.0v (single cell) or 5.8v (2-cell)...........that is if one circuit serves both cases?

So there has to be 2 versions or there must be some way that the driver stores in memory the voltage when batteries are first inserted to know that its a single cell or 2 cell.

Just a thought.

 

[texas cop]

Sorry I may have worded my question wrong. The LED I want to use is a 6 volt LED, most operate at a much lower voltage. Will 2 or more cell drivers provide not only the same amperage but the needed higher voltage.

 

[hiuintahs]

Sorry I may have worded my question wrong. The LED I want to use is a 6 volt LED, most operate at a much lower voltage. Will 2 or more cell drivers provide not only the same amperage but the needed higher voltage.

I had to go to Cree's web page and read up on the MT-G2. My first thoughts was that it was a module that was powered by either 6, 9 or 36 volts with its own driver built in. I had no idea that there would be discrete led's that have a forward voltage drop of 6v. In the specs it says 5.7v typical forward voltage drop at 1100mA..........so I guess it is a discrete LED.

With the driver that you are looking at, high output is 3A. That driver is designed to work with leds that have forward voltage drops of around 3 volts...........that's 9 watts..........quite a bit of power for such a small driver circuit as it is. If that driver is current regulated, then it will attempt to move the output voltage to 6 volts so as to push 3A through the LED. Now we're talking twice the output power for the same current, twice the current in the step down inductor and mosfet switching elements in the circuit. My thoughts are that if it did work, it might die prematurely. I doubt its robust enough.

 

[PeterH]

6 volts for an LED would be either 2 LEDs series in a package or an LED with some kind of current limiter. As best I can make out from the datasheet, the MT-G2 6V is the former.

 

[kosPap]

I found this today. http://intl-outdoor.com/ld2c-3a-12-cell-circuit-board-p-732.html Question is I want to use it in a tight space to run an MT-G2, will it provide the proper voltage along with the current off of 2 cells? I understand only a little about drivers, along with the regulated current they provide how do they detect the proper voltage to push?

I had been searching for a driver for precisely this setup. I do nto rememer which it was that i found but it was a LD-xx series driver for 2 batteries and 3 LEDs....diamtre was 26mm.
You can search for it in intl-outdoor and cnqualitygoods

 

[hoffmyster86]

reading through here, i have a question about the voltage outputs on drivers in general?

some state 2v or 3v less than the battery on the output, most say nothing more than a voltage input range and 'constant current'.

now i know from exsperimenting as long as the currents constant a few more volts makes very little or no diference in the brightness (es the watts add up to more)..
so do most drivers just let the volts through and just control the ampage?

 

[hiuintahs]

reading through here, i have a question about the voltage outputs on drivers in general?

some state 2v or 3v less than the battery on the output, most say nothing more than a voltage input range and 'constant current'.

now i know from exsperimenting as long as the currents constant a few more volts makes very little or no diference in the brightness (es the watts add up to more)..
so do most drivers just let the volts through and just control the ampage?

When it comes to "regulating" an output, what the driver circuitry does is regulate the output voltage such that the desired constant current is achieved........if it is a regulated current output type of driver which are the best.

An LED's brightness is determined by the amount of current being passed through it. But before any current will pass through an LED, the voltage on the LED has to be at or slightly above its forward voltage (Vf)........which is dependent on the model of LED........but its around 3 volts. At that point the LED starts to turn on but it doesn't take very much more voltage for the LED to actually even be damaged if the source can provide the current.

It's not a linear response. It's a fairly tight knee from off to fully on. So the best way to control the brightness on an LED is to manage the current through it which lets the driver circuit put out whatever voltage it needs to, to meet this current.

When you see voltage requirements of drivers its the maximum or minimum required input voltage such that the driver circuit works properly. Integrated circuits that operated down at very low voltages tend to be such that they are not tolerant to high voltages. Thus some of these driver circuits are very specific that you do not exceed their maximum voltage input. Being too low just means it won't work properly.

Hope this helps.

 

[hoffmyster86]

When it comes to "regulating" an output, what the driver circuitry does is regulate the output voltage such that the desired constant current is achieved........if it is a regulated current output type of driver which are the best.

An LED's brightness is determined by the amount of current being passed through it. But before any current will pass through an LED, the voltage on the LED has to be at or slightly above its forward voltage (Vf)........which is dependent on the model of LED........but its around 3 volts. At that point the LED starts to turn on but it doesn't take very much more voltage for the LED to actually even be damaged if the source can provide the current.

It's not a linear response. It's a fairly tight knee from off to fully on. So the best way to control the brightness on an LED is to manage the current through it which lets the driver circuit put out whatever voltage it needs to, to meet this current.

When you see voltage requirements of drivers its the maximum or minimum required input voltage such that the driver circuit works properly. Integrated circuits that operated down at very low voltages tend to be such that they are not tolerant to high voltages. Thus some of these driver circuits are very specific that you do not exceed their maximum voltage input. Being too low just means it won't work properly.

Hope this helps.

dose that man any 'exsess' voltage is let through to the LED so to speek, and the currents controlled.

 

[hiuintahs]

No. The way it works is that power out = power in minus the amount of power loss by the driver.

Let's say that a driver circuit operates between 3 to 7 volts such as you'd find with 2x CR123A lights or 18650 lights. At battery voltage of 3 volts it will draw a lot more current from the battery. At 7 volts it would draw half as much.

Power is voltage x current. If the Vf of the LED is 3.25v and the driver is running 1amp through it. Then you have 3.25 watts output. The input wattage will be around 3.9 watts which is 20% higher due to the losses consumed by the driver circuit.

So if the driver circuit is well designed and can hold constant current to the LED for a battery input between 3 volts and 7 volts, what you will see is that the battery is sourcing 3.90/3 = 1.30 amps when at 3 volts and will source 3.90/7 = 0.557amps when at 7 volts.

 

[hoffmyster86]

No. The way it works is that power out = power in minus the amount of power loss by the driver.

Let's say that a driver circuit operates between 3 to 7 volts such as you'd find with 2x CR123A lights or 18650 lights. At battery voltage of 3 volts it will draw a lot more current from the battery. At 7 volts it would draw half as much.

Power is voltage x current. If the Vf of the LED is 3.25v and the driver is running 1amp through it. Then you have 3.25 watts output. The input wattage will be around 3.9 watts which is 20% higher due to the losses consumed by the driver circuit.

So if the driver circuit is well designed and can hold constant current to the LED for a battery input between 3 volts and 7 volts, what you will see is that the battery is sourcing 3.90/3 = 1.30 amps when at 3 volts and will source 3.90/7 = 0.557amps when at 7 volts.

hmm, so theyre working on 'wats', are they pulsed?

 

[hiuintahs]

No, Watts is just the measure of power (volts x current). Everything consumes power and the most efficient drivers consume the least amount of power. Thus power out always = power in minus the amount of power that is lost in the driver circuit.

PWM (pulse width modulated), current regulated, and linear (ie: allowing a voltage regulator or series resistor to limit the current) are the only means to drive an LED.

Again you cannot just put a voltage on an LED as it will not turn on if below Vf or the LED will burn up if the voltage is above the Vf such that the maximum current through the LED is exceeded.

Some type of current limit has to be provided. The cheap method is to have a voltage above the Vf of the LED and just place a series resistor in series with the LED. That is what you typically get with the cheap 3xAAA lights..........and why they use 3 batteries (to get the voltage up high above the Vf) so that they don't have to have any fancy regulator circuit.

 

[hoffmyster86]

No, Watts is just the measure of power (volts x current). Everything consumes power and the most efficient drivers consume the least amount of power. Thus power out always = power in minus the amount of power that is lost in the driver circuit.

PWM (pulse width modulated), current regulated, and linear (ie: allowing a voltage regulator or series resistor to limit the current) are the only means to drive an LED.

Again you cannot just put a voltage on an LED as it will not turn on if below Vf or the LED will burn up if the voltage is above the Vf such that the maximum current through the LED is exceeded.

Some type of current limit has to be provided. The cheap method is to have a voltage above the Vf of the LED and just place a series resistor in series with the LED. That is what you typically get with the cheap 3xAAA lights..........and why they use 3 batteries (to get the voltage up high above the Vf) so that they don't have to have any fancy regulator circuit.

i've notised some drivers dwindle the brightnes whilste otheres are exselent.. apart from that thank you.