eem2am
Banned
16 pwm chip
hello
i am using LTC1871 as a constant current led driver in boost mode (12 to 28v) at 10W.
The current sense for the fet source pin is 150mV......but the reference for the current in the LED string is set at 1.23V.
This would give high dissipation in the led current sense resistor of 1.23*0.35 = ~0.5Watt.
therefore, i have biased up the voltage on the sense pin by "dribbling some current from the 5v ref pin, thru some resistors to bias up the voltage , so as to decrease dissipation in the sense resistor.
do you thin this will interfere with the chips internal slope copensation, or give any other problems? ...............................
R8 and R9 are used to help me reduce the dissipation in the current sense resistor in series with the leds. R6 would dissipate much more power if i didnt use R8 and R9.
by the way, i am using LTC1871 because no LED driver chips have a RUN pin on them and we need this. -implementing the run function can be done with external components but too many.
Added after 42 minutes:
...sorry, here is the LTC1871 datasheet...
http://cds.linear.com/docs/Datasheet/1871fe.pdf
hello
i am using LTC1871 as a constant current led driver in boost mode (12 to 28v) at 10W.
The current sense for the fet source pin is 150mV......but the reference for the current in the LED string is set at 1.23V.
This would give high dissipation in the led current sense resistor of 1.23*0.35 = ~0.5Watt.
therefore, i have biased up the voltage on the sense pin by "dribbling some current from the 5v ref pin, thru some resistors to bias up the voltage , so as to decrease dissipation in the sense resistor.
do you thin this will interfere with the chips internal slope copensation, or give any other problems? ...............................
R8 and R9 are used to help me reduce the dissipation in the current sense resistor in series with the leds. R6 would dissipate much more power if i didnt use R8 and R9.
by the way, i am using LTC1871 because no LED driver chips have a RUN pin on them and we need this. -implementing the run function can be done with external components but too many.
Added after 42 minutes:
...sorry, here is the LTC1871 datasheet...
http://cds.linear.com/docs/Datasheet/1871fe.pdf