White or Blue high bright (HB) LEDs have a threshold is near 2.5 but ESR linear asymptote is around 2.85 and actual Vf forward voltage depends on W capacity * ESR of LED
.
Has i said, i will eagerly await the outcome of this subject [many thanks] ... And thx to 'Zasto' for his observations.
... I am hoping to run a single LED light [white or blue], for approximately 360hrs [minimum] before changing the batteries ...
My only other requirement is to avoid any external wiring, or plugs.
Kind regards, Vince
If you search my threads you will find many graphs which show that all semiconductors saturate and have a more linear bulk resistance. Bigger means lower losses and high current ratings.
For LED's they do not specify ESR but you can determine it from the tangent slope of the saturated VI curve. The same is true for any diode. From this you can estimate the forward voltage rise.
Which comes first? The cart or the horse?
We do not know which LED you will use [Vf is critical].
We do not know at what current you will operate the LED at.
If you determined the LED and current first, then choosing the battery is easier.
That said, start with a 3.7 Li-Ion Rechargeable Battery of at least 3600mAH [to run your LED at 5mA].
I understand the VI curves, just fine. Although I suggest keeping the scope of the discussion restricted to LEDs at present.What do you understand on VI curves on batteries, diodes , transistors and MOSFETs and the thermal effects? anything?
ESR is is just the incremental resistance in series with a junction fixed voltage drop. Thus from the VI curve slope or tangent = dv/di, which you can extract from a plot or a table of numbers.
I usually use 10% of rated to 200% current but depends on the tolerance range of the voltage available. It basically allows you to use Ohm's law for impedance ratios required on % tolerance voltage regulation or current regulation.
.
V | I | ESR | P | Watt-Ω's | Vled | Error |
2.70 | 0.08 | 2.00 | 0.216 | 0.43 | 2.742 | 1.6% |
2.80 | 0.22 | 0.71 | 0.616 | 0.44 | 2.798 | -0.1% |
2.90 | 0.47 | 0.40 | 1.3659 | 0.54 | 2.8984 | -0.1% |
3.00 | 0.86 | 0.26 | 2.583 | 0.66 | 3.0544 | 1.8% |
@Kam
Is this relating to the two points on the VI curve? So your first point in determining the slope is 10% of the rated current, and the second point is 200% !!!
Why 200%!
Is not very non-linear at that point?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?
We use cookies and similar technologies for the following purposes:
Do you accept cookies and these technologies?