eem2am
Banned
constant current smps design
Hello,
I am looking at this constant current LED driver.....
it is from this app note:-
http://www.powerint.com/sites/default/files/PDFFiles/der185.pdf
...it claims to be able to do constant current driving of LEDs ...without needing to sense the output current (!)
.......however, do you agree with me that even though after switch ON, the output current would eventually become constant, one cannot closely tell what the constant current would actually be (!) ?
i can't see the use of constant current LED driving if you can't fix the constant current level.
after all, when a LED light like this is switched ON, the dynamic resistance of the LEDs will not be a known value (since the LEDs may or may not be warm from just having been ON).
here is the datasheet for the LNK605...
http://www.powerint.com/sites/default/files/product-docs/linkswitch-ii_family_datasheet.pdf
-------------------
Page 8 (bottom) of the following App Note....
http://www.powerint.com/sites/default/files/PDFFiles/der185.pdf
...gives an explanation of the Constant Current mechanism in LNK605.............
--------------------
"While the LNK605DG operates in the CV region, it regulates the output voltage by
ON/OFF control. It maintains the output voltage level by adjusting the ratio of enabled
cycles to disabled cycles. This also optimizes the efficiency of the converter over the
entire load range.
When the LNK605DG enters a state where no switching cycles are skipped (concurrent
with the maximum power point) the controller within the LinkSwitch-II transitions into CC
mode. A further increase in the demand for load current causes the output voltage to
drop. This drop in output voltage is reflected on the FB pin voltage. In response to this
voltage reduction at the FB pin, the switching frequency is reduced to achieve constant
output current."
------------------
My question is , what is the point of constant current LED drive with this LNK605, if we cannot closely specify what the particular constant current actually is ?
...my LEDs will likely just fry, am i wrong?
thanks in advance and sorry for long post
Hello,
I am looking at this constant current LED driver.....
it is from this app note:-
http://www.powerint.com/sites/default/files/PDFFiles/der185.pdf
...it claims to be able to do constant current driving of LEDs ...without needing to sense the output current (!)
.......however, do you agree with me that even though after switch ON, the output current would eventually become constant, one cannot closely tell what the constant current would actually be (!) ?
i can't see the use of constant current LED driving if you can't fix the constant current level.
after all, when a LED light like this is switched ON, the dynamic resistance of the LEDs will not be a known value (since the LEDs may or may not be warm from just having been ON).
here is the datasheet for the LNK605...
http://www.powerint.com/sites/default/files/product-docs/linkswitch-ii_family_datasheet.pdf
-------------------
Page 8 (bottom) of the following App Note....
http://www.powerint.com/sites/default/files/PDFFiles/der185.pdf
...gives an explanation of the Constant Current mechanism in LNK605.............
--------------------
"While the LNK605DG operates in the CV region, it regulates the output voltage by
ON/OFF control. It maintains the output voltage level by adjusting the ratio of enabled
cycles to disabled cycles. This also optimizes the efficiency of the converter over the
entire load range.
When the LNK605DG enters a state where no switching cycles are skipped (concurrent
with the maximum power point) the controller within the LinkSwitch-II transitions into CC
mode. A further increase in the demand for load current causes the output voltage to
drop. This drop in output voltage is reflected on the FB pin voltage. In response to this
voltage reduction at the FB pin, the switching frequency is reduced to achieve constant
output current."
------------------
My question is , what is the point of constant current LED drive with this LNK605, if we cannot closely specify what the particular constant current actually is ?
...my LEDs will likely just fry, am i wrong?
thanks in advance and sorry for long post