Thank-you, and once again, thanx.
How is it that one model of driver can power led's with different vf's ?
Let's take a Souel P4, 'I' bin with a voltage forward of 3.25-3.50 volts.
A two-mode buck current regulating board will drive it at the output the user selects, for example 80ma, 700ma. Back to what you wrote in your post, "some circuits drop down the voltage," how is that set? for example, I know that I could use a different emitter with say a vf of 3.75-4.00v, and it would still work too, at the regulated current levels that the driver board lets me select (80ma, 700ma).
As most drivers regulate current, what happens to voltage? Both as the cells are depleted and voltage drops down from 4.2v to 3.5v
and, how does this change across emitters with different vf's.
What any current regulator does is this: meausre the current through the deice, then vary the voltage supplied to the LED accordingly in order to maintain a particuilar constant current. If an LED has a lower Vf, the driver will supply a lower voltage in order to still see 80mA. If an LED heats up and CHANGES Vf, current will start to increase, the driver will sense this, then back off the voltage slighltly until the current settles back down to 80mA again.
In the case of a buck driver, this process continues to work so long as the input voltage is higher than the required output voltage. If the input voltage drops below the Vf of the LED, the driver can basically do nothing -- it requires a certain voltage "overhead" to operate. Some drivers on the other hand, such as buck-boost drivers, can actually continue to operate by stepping UP the input voltage.
From an exernal point of view, youi could expect to see soemthing like this:
LED with a Vf of 3V, and output current of 1000mA:
10Vin, 350mA in
6V in, 550mA in
4V in, 800mA in
3V in, 1080mA in
2V in, 1650mA in
1.5V in, 2400mA in
Input power (voltage * current) will always be close to output power. Howver, efficiency will tend to be better as the voltage input is closer to the voltage output, as the driver will have less "Work" to do.
anytime there is a significant mismatch between input voltage and output voltage, that means a lot of energy will have to be stored in energy storing elements (such as inductor or capacitor) inside the driver. If input voltage is close to output voltage, the regular doesn't have to really do much, and can simply let the voltage "straight through" without storing up energy and converting the voltage.
(lastly, please confirm this: a driver regulates current by adjusting the 'duty cycle' this means the circuit from the cell to the emitter is completed, or power is drawn from the cell, in quickly cycling 'off / on' (the pulse width modulation) The chip has a separate circuit that remains charged so the chip remains 'on' and is able to monitor the current. So a driver could be over volted and fried (e.g., a max 6v driver connected to 20 IMR16340 in series), but a current regulating driver cannot be over amped simply by connecting a large power supply (e.g., same 6v driver connected to 20 IMR16340 in parrallel) as the driver regulates the current that is drawn from the power supply)
Connecting more batteries in parallel doesn't necessarily "increase the current." It increases the amount of charge available (in mAh), and decreases the equivalent internal resistance of the battery. That means that if you were to connect 20 IMR batteries in parallel to a very demanding load (that is low resistance, or resistance comprable to the internal resistance of a single battery) -- such as a high power incandescent lamp -- the 20 IMR batteries would be capable of supplying more current than a single IMR battery. This is because for a single cell a lot of the energy will be absorbed by the cells own internal resistance. Running cells in parallel reduces this.
However of you were to connect first a single cell, then 20 cells in parallel to a relatively modest load (that is, a device whose resistance is much larger than the internal resistance of a single cell), the 20 batteries in parallel would provide the exact same amount of current as a single cell , but would just last 20 times longer.
that just came out. I've been reading a lot before assembling my first light from scratch.
