Buck Circuit; Summary; Figure 1-2 Simplified Buck Circuit; Figure 1-3 Current On Load - Samsung S3F84A5 Application Note

S3F84P4_AN_REV0.00 (PRELIMINARY SPEC)

1.3.1 BUCK CIRCUIT

Buck circuit works when a switch signal turns on the transistor (Q). The DC power then starts to charge the coil
(L). When the current reaches a predefined level, change the transistor state from On to Off using the switch
signal. At this time, since the coil will have inertia to keep the current direction, the load still can be powered with a
freewheeling diode until the switch signal turns on the transistor again. The resulting current is continuous but
alternating (see Figure 1-3

1.3.2 SUMMARY


The average current over load is determined by the duty cycle of switch signal.

SMPS can lead to current ripple. But it could be alleviated by increasing the PWM frequency or coil
inductance value, or by adding extra filtering circuits.
Figure 1-2
for more details).
Figure 1-3
Samsung Confidential
1 OVERVIEW OF HPLED LIGHTING CONTROL SYSTEM
Simplified Buck Circuit
Current on load
9