FIXED FREQUENCY WHITE LED DRIVER

FSP3301

2007-4-16

3/9

FUNCTIONAL BLOCK DIAGRAM

FUNCTION DESCRIPTION

The FSP3301 uses a constant frequency, current mode control scheme to provide excellent line and load regulation.

operation can be best understood by referring to the block diagram. At the start of each oscillator cycle, the SR latch

is set, which turns on the power switch Q1. A voltage proportional to the switch current is added to a stabilizing ramp

and the resulting sum is fed into the positive terminal of the PWM comparator A2. When this voltage exceeds the level

at the negative input of A2, the SR latch is reset turning off the power switch. The level at the negative input of A2 is

set by the error amplifier A1, and is simply an amplified version of the difference between the negative input of A3 is

set by the difference between the feedback voltage and the reference voltage of 100mV. In this manner, the error

amplifier sets the correct peak current level to keep the output in regulation. If the error amplifier’s output increases,

more current is delivered to the output; if it decreases, less current is delivered.

TYPICAL APPLICATIONS CIRCUIT