Reference Circuit 4381

MR-16 LED Driver with a 5V Auxiliary Output to Power a Pulsating LED Cooler



Overview

This reference design details a driver circuit using the MAX16820 hysteretic LED driver for a 4-LED MR-16 lamp with an associated power source (MAX5033) for a pulsed air cooler.

The following are the electrical input requirements and output capabilities.

VIN: 24VDC ±5%
Temperature: +80°C (max) ambient
VLED configuration: 4 LEDs in series (16VDC, max), 750mA
Auxiliary output power: 5V at 150mA (average), 300mA (peak)

The reference design is discussed in detail below, with analysis of the main circuit blocks and layout considerations.

Figure 1. Schematic of the driver design.
Figure 1. Schematic of the driver design.

Figure 2. Photo of the PCB. The board was designed to fit directly into an MR-16 assembly.
Figure 2. Photo of the PCB. The board was designed to fit directly into an MR-16 assembly.

Figure 3. Revised layout of the PCB (updated from the board in Figure 2).
Figure 3. Revised layout of the PCB (updated from the board in Figure 2).

Overview

This reference design details a driver circuit using the MAX16820 hysteretic LED driver for a 4-LED MR-16 lamp with an associated power source (MAX5033) for a pulsed air cooler.

The following are the electrical input requirements and output capabilities.

VIN: 24VDC ±5%
Temperature: +80°C (max) ambient
VLED configuration: 4 LEDs in series (16VDC, max), 750mA
Auxiliary output power: 5V at 150mA (average), 300mA (peak)

The reference design is discussed in detail below, with analysis of the main circuit blocks and layout considerations.

Figure 1. Schematic of the driver design.
Figure 1. Schematic of the driver design.

Figure 2. Photo of the PCB. The board was designed to fit directly into an MR-16 assembly.
Figure 2. Photo of the PCB. The board was designed to fit directly into an MR-16 assembly.

Figure 3. Revised layout of the PCB (updated from the board in Figure 2).
Figure 3. Revised layout of the PCB (updated from the board in Figure 2).

Design Analysis

Designed to fit directly into an MR-16 assembly, this reference design delivers 750mA to a string of 4 LEDs from a 24V power source. The MAX16820 provides hysteretic control and regulates the current through the inductor and the LEDs. Meanwhile, the MAX5033 provides power to a pulsating cooler through the J2 connector. The cooler presents a sinusoidal load of 300mA peak and 150mA average to the power supply.

The R3 resistor is in the circuit to satisfy the stability requirements (with a ceramic outputcapacitor) of the MAX5033.

A provision was made for PWMing, but not tested. The center pin of J1 was routed directly to the DIM input of the MAX16820.

Power-Up Procedure

  1. Connect 4 LEDs in series to the LED+ (anode) and LED- (cathode) pins.
  2. Attach a 300mA load to J2.
  3. Attach a 24V, 1A power supply to J1.
  4. Turn on the power supply.
Table 1. Bill of Materials (BOM)
Designator Component Description Footprint Quantity
C1 Nonpolarized capacitor 10µF, 50V, X7R 2220 1
C2 Nonpolarized capacitor 470pF, 50V, COG 0402 1
C3 Nonpolarized capacitor 1µF, 16V, X7R 0603 1
C4, C5 Nonpolarized capacitors 0.1µF, 25V, X7R 0603 2
C6, C7 Nonpolarized capacitors 10µF, 10V, X7R 1206 2
D1 Schottky diode STPS2L60A SMA 1
D2 Schottky diode RB160M-60 SOD123F 1
J1 3 x 1 connector 1.25mm 1
J2 2 x 1 connector 100mil 1
L1 Inductor 82µH, MSS1038-823 10.2mm x 10mm 1
L2 Inductor 390µH, MSS1038-394 10.2mm x 10mm 1
Q1 n-channel MOSFET 2SK2857 SOT89 1
R1 Resistor 0.24Ω, 1% 1206 1
R2 Resistor 10kΩ, 1% 0603 1
R3 Resistor 0.27Ω, 5% 1206 1
R4 Resistor 100kΩ, 1% 0603 1
R5 Resistor 10kΩ, 1% 0603 1
U1 LED driver MAX16820ATT 6-TDFN 1
U2 Buck DC-DC converter MAX5033BUSA 8-SO 1

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MAX16820
2MHz High-Brightness LED Drivers with High-Side Current Sense and 5000:1 Dimming

  • Simple High-Power LED Lighting Design with Accurate LED Current Control
  • Wide Dimming Range (5000:1)
  • Minimizes Number of Components to Save Space and Cost

MAX5033
500mA, 76V, High-Efficiency, MAXPower Step-Down DC-DC Converter

  • Wide 7.5V to 76V Input Voltage Range
  • Fixed (3.3V, 5V, 12V) and Adjustable (1.25V to 13.2V) Voltage Versions
  • 500mA Output Current