Boost driver for long LED strings

The long strings of LEDs commonly found in TV and display backlighting, street lights, and parking garage lights require a current driver capable of producing high voltages. This reference design provides such a driver using the MAX16834, and demonstrates how very-high dimming ratios can be obtained.

This is a reference design for a boost LED driver using the MAX16834 for long strings of LEDs. This application is for LED backlighting for large LCD TVs or displays as well as streetlights and parking garage lights.

V_IN: 24VDC ±5% (at 1.22A)
V_LED Config.: 23 LEDs in series (75V) at 350mA.
Dimming: As low as a 3.33µs on-pulse (3000:1 dimming ratio when the dimming frequency = 100Hz).

Note: this design has been built and tested. However, detailed testing has not occurred and there may be nuances that are yet to be discovered.


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Figure 1. The LED driver board.


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Figure 2. Schematic of the LED driver.


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Figure 3. Layout of the LED driver.


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Figure 4. Bill of materials.


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Figure 5. Design spreadsheet. To get the spreadsheet for use in your design, contact your local Maxim sales office.


Figure 6. Drain voltage and current-sense resistor voltage (50mΩ).


Figure 7.电感器生产 Drain voltage risetime.


Figure 8. Output voltage (AC coupled) and sense-resistor voltage.


Figure 9. Figure 9. High dimming ratio (on-time < 4µs).


Figure 10. Inductor temperature rise. The calculator is available from Coilcraft®.

Circuit description

Overview

This reference design is f插件电感or a high-voltage, boost current source for very long strings of LEDs. Applications include LCD TV backlighting, LCD monitor backlighting, streetlights, and parking garage lights. Long LED strings can be a very cost-effective way to drive LEDs. Also, since the LEDs will have exactly the same current, brightness variations are nicely controlled. This design has a 24V input, up to an 80V LED output, and drives 350mA through the LED string. The measured input power is 29.3W and the output power is 26.4W for about 90% efficiency.

PCB

The printed circuit board (PCB) is a general-purpose board for MAX16834 boost designs (Figures 1 and 3). Therefore, there are many components that are either shorted or not populated. These components are indicated on the schematic (Figure 2). Figure 4 shows a bill of materials for this design.

Topology

This design is for a 300kHz discontinuous-boost regulator. In Figure 5, the spreadsheet printout shows the calculated RMS and peak currents in the MOSFET and inductor. Discontinuous designs do, admittedly, have some disadvantages, nota升压电感bly higher MOSFET a功率电感nd inductor currents.平面变压器厂家 | 平面电感厂家

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