1. I have to drive a white led. Input voltage is 6V-8.4V. I need to vary the intensity using a potentiometer.
2. Using the ckt as in attached image. Not using optional output ripple filter. Ckt shows use of HV version, but I am using normal version of LM2576
3. Directly connected the outout to white led. Max output voltage set to 3.7V. Instead of using 1N5822, I have used SS34 diode.
R1 = 5K fixed
R2 = 10k(pot)
Calculated using formula:
Vout = Vref(1 + R2/R1)
Vref = 1.23V, R1 between 1K & 5K
By fixing r1=5K, R2 value comes out to be 10K
Problem:
1. When I rotate the pot from one end to another, led brightness smoothly decreased.
2. But when it is at max end, i.e output voltage at 3.7V, & slighlty rotate the pot in another direction, suddenly the output voltage drops to 3.05V & there is noise starts from regulator also. Which causes sudden dim in led
And if further move down the pot, the voltage now rises to 3.5V & after that voltage decreases smoothly.
This sudden drop/noise problem only occur when I slightly drop the value from 3.7Vout.