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This circuit is designed to drive an array of four series-connected InGaN white LEDs (typical Vf = 16.2V total) at a continuous current of 330 mA from an input of 24V +-10%. Switching frequency is approximately 1.2 MHz to provide the smallest component footprint and LED ripple current possible.
Ripple current in the LED array is > 2 mA pk-pk, or less than 1% of the average LED current.
To modify this design while keeping switching frequency as high as possible, follow these steps:
1. Determine duty cycle, D = (Vf_total + 0.2V - 0.5V) / (Vin - 0.5V)
2. Determine Ton, Ton = 300ns / (1/D - 1)
3. With Ton, calculate Ron, Ron = (Ton * Vin) / (1.42E-10)
4. With Ron, calculate Fsw-max, Fsw-max = Vout / (1.42E-10 * Ron)
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Example Schematic Showing Connection for all Components.
