Re: Triple thick BiTT

Body

The figure went missing here it is (hopefully) else the link to it:
https://www.maximintegrated.com/en/images/appnotes/3070/3070Fig07.gif https://www.maximintegrated.com/en/images/appnotes/3070/3070Fig07.gif


Regards
Ole


---In [email protected], <onielsen@...> wrote :

 Hi Kone,

"You say if limiting circuit to limit current in the LED the current remains constant"
If it has a build in switching regulator the current decrease when the voltage increase. This makes the power stay constant. Without any measurement or datasheet of the LED lamp we just don't know.

"if say only 8V applied, the current will be lower"
Yes. Perhaps not even enough current will flow to make the lamp light.

Take a look at the voltage current characteristics of some white LEDs at the following figure taken from here: https://www.maximintegrated.com/en/app-notes/index.mvp/id/3070 https://www.maximintegrated.com/en/app-notes/index.mvp/id/3070


Figure 7. These curves illustrate the considerable differences in current-voltage characteristics for white LEDs, even those randomly selected from the same production lot. Operating several such LEDs in parallel at a constant 3.3V (the upper dotted line) therefore produces different shades of white and different brightnesses.

A 12V LED lamp may have 3 LEDs in series and a resistor to drop the remaining voltage. At 8V each LED will get below 3V which may not make them light up.

"Also if the non-linear character of LED lights/diodes does affect the current when more voltage is applied then it is rated at, what would be the "percentage" of difference from ohms-law calculated watts?"
The datasheet of the LED is needed to know this. He could make his own curve for the particular LED lamp by measuring the voltage and current at different values. Or he could just make a measurement at the particular voltage of interest (16.95V) to know.

Regards
Ole
 

---In [email protected], <konehead@...> wrote :

 Hi Ole
 Other BiTT demos on youtube show X3 watts out compared to in, so maybe Kurt is being conservative in how he measures actually.
 I am to a ltitle bit disappointed he did not just put an anlog and/or digital mulmeter reading the amps into that LED light. 
 But when I work with LEDs analog will give the same reading as multimeters so if analog it is simply a resistive load (heat) applied inside the meter and needle goes up correspondingly so it really does not bother me too much he did not do a meter.;
 You say if limiting circuit to limit current in the LED the current remains constant -  I would call it in my limited understanding  (almopst a pun haha)  current is  "limited" to a certain level actually that the LED circuit  will not permit itself to pull into itself....if say only 8V applied, the current will be lower, if 17V the current will be at its maximum allowed so I don't see what your point is here! (seems to me at least sorry)
  If resistorsi there to limit currentr, that is part of the resistance of the LED given already, and like you say there will be MORE corrent than he shows if so, so again I dojnt see the point....
 .
 Also if the non-linear character of LED lights/diodes does affect the current when more voltage is applied then it is rated at, what would be the "percentage" of difference from ohms-law calculated watts? 10%? 20%? even if 50% change in the current being lower than calculated with ohms law, it is still "unity" 
 

 Kurt does show the primary is not affected by the loading of secondaries and that in itself is pretty good expecially compared to standard transformers...
 ciao
 Kone