COT Drivers Control LED Ripple Current
by Chris Richardson, National Semiconductor, Vendor website, Sep 23 2008
Focus:
By providing control over ripple current and switching frequency, a constant-ripple buck LED
driver design based on the LM3404 driver IC enables designers to tradeoff parameters such as
LED light output and reliability with parameters such as design size and cost. This driver
design uses a variation of constant-on-time control (quasi-hysteretic) in which switching
frequency is not constant (as it usually is with this technique) and varies with input voltage
and output voltage. Because this design controls average current and ripple current
independently of output voltage, it can drive LED strings of varying length. So this driver
design may be paired with an ac-dc supply to create a "universal" current source.
What you’ll learn:
- How to build a constant-ripple buck LED driver
- How to build a universal current source for LED strings of varying length
Notes:
National Semiconductor Application Note 1853
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