Other Parts Discussed in Thread: LM3423, LM3421
Hi
Question on Buck-Boost Application ( Refer to datasheet "LM342x/-Q1 N-Channel Controllers for Constant-Current LED Drivers", SNVS574F –JULY 2008–REVISED JULY 2015)
1. Can I use LM3423 to replace LM3421 in the application circuits on Pg 55 , Figure 41.
2. I intend to use LM3423 to control 4 Lighting LEDs place in series on the application circuits on Page 55, Figure 41.
Lighting LED specs : Absolute Max V reversed = 1V, Absolute Forward current max = 1A, Vforward = 3.5V
I intend to set the LED Average current to 0.7A by setting up the Rsns , Rhsp and Rcsh
i. May I know what the voltage at D1's cathode. with respect to Q2's Drain if my input voltage is 24V
ii. Also since Vin take in Dynamic range 10V to 70V.. When Vin drop from 70V to 10V during the time when Q1 is turn ON.. Will there will be a reverse Voltage across my 4 LEDs ( Since my lighting LED absolute reverse max volt is 1V, so , total withstanding voltage is 4V only )Will this damage my 4 lighting LEDs in Series?