Constant, Off-time, Buck-based, LED Drivers Using the HV9910B

Focus:

Constant-frequency, peak-current-controlled buck converters offer fair regulation of LED current with wide variations in input and output voltages. These converters are also simple to design since they need no feedback compensation and they respond very quickly to PWM dimming. Unfortunately, these converters experience sub-harmonic oscillations at duty cycles above 50%. However, changing from constant-frequency to constant off-time operation, where off-time is fixed and on-time varies with the current-sense signal, allows the buck converter to operate with stability at duty cycles above 50%. Operation of the HV9910B controller IC, which allows either constant frequency or constant off time, is explained and the part is used in a detailed design example of a constant off-time buck converter.

What you’ll learn:

• How to design a peak-current-controlled buck LED driver that operates at duty cycles above 50%

Notes:

Supertex Application Note AN-H50

View the Source

Author & Publication:

no author listed, Supertex, Vendor website, Feb 25 2009

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