Power Electronics

LED Driver Employs Fixed-Frequency Switching

Catalyst Semiconductor’s CAT4238 is a high-voltage boost converter designed to drive up to 10 LEDs. Many high-voltage boost converters typically use a simple variable-frequency switching scheme. This approach results in a wide range of unwanted harmonics, which are not easy to filter or eliminate. In contrast, the CAT4238 uses a fixed-frequency (1-MHz) switching architecture, making it ideal for low noise applications.

A high-voltage CMOS output stage in the device allows large LED strings (up to 38 V) to be accurately biased and regulated from a low-voltage input supply while still delivering 87% efficiency. To eliminate excessive inrush currents, which can occur during initial power-up, the CAT4238 offers an integrated soft-start control. In the event of an open-LED fault condition, an internal over-voltage protection circuit will place the device into a low-power operating mode restricting the output voltage to safe levels without the need for external circuitry. Both of these features are fully integrated, eliminating the need for external components.

Other features include a quiescent ground current of 0.6 mA, a shutdown current of less than 1 µA, and an automatic shutdown at 1.9 V (UVLO). The CAT4238 is available in a low-profile, 5-lead thin SOT23. Unit pricing in 10,000-piece quantities is $0.78 each. Samples and evaluation kits are now available.

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