Boost-Buck LED Driver Topology for Automotive LEDs
Operates with Low Input and Output Ripple
Keith Szolusha Automotive LED drivers often require step-up/step-down DC/DC converters that
can produce constant current at a voltage stepped up and stepped down from
a varying input voltage (battery). Another important requirement for automotive
applications is low EMI, namely, low input and output ripple. EMI requirements
can be difficult to satisfy, as few of the most commonly used step-up/step-down
DC/DC converter topologies can operate with both low input and low output
ripple, while also meeting other requirements. These demands, however, are easily
met by the unique, patent-pending, boost-buck topology described here.
This new topology is not the only stepup/step-down topology available. There
are a number of other topologies that
can convert a wide-ranging input voltage to a VLED within that range. The most
commonly used nonisolated step-up/
step-down LED driver topologies include: 4-switch buck-boost for very
high power and efficiency The overall size of the combined boostbuck inductors (or coupled inductor) is similar to the single inductor in buck-boost mode. The input ripple
is similar to a SEPIC, but the output
ripple is much lower. The inductor size LED– Figure 1. The LT3952 8V–36V input to 6V–18V LED 1A boostbuck LED driver has low input and output ripple with 300:1
PWM dimming capability at 120Hz and 90% efficiency. There are advantages to each of these
topologies, but none can produce both
truly low input and output ripple. Linear
Technology’s patent-pending “boostbuck” (boost-then-buck-mode) floating
output LED driver topology features …