Selecting Inductors to Drive LEDs

Application Design Example

LED lighting is an exciting and fast growing application. LEDs can provide low cost, reliable lighting for a wide variety of applications ranging from architectural and automotive to signage and handheld devices. The designer faces the challenge of choosing from a vast array of LED manufacturers and device styles. Equally challenging can be the selection of components for the LED driver circuit. Fortunately, powerful tools are available that greatly facilitate the power inductor selection.

Since LED applications can use LEDs individually as well as parallel or serial arrays, the driver circuit may need to be a voltage step-up, step-down, or both. The Coilcraft DC-DC Optimizer tool (https://www.coilcraft.com/en-us/ tools/dc-dc-optimizer/#/search) can be used to select the inductor for all of these driver circuit configurations.

Buck Converter Example

This example demonstrates the use of the Coilcraft DC-DC Optimizer tool to select the inductor for a Texas Instruments Buck LED driver reference design based on the LED Driver TPS92515-Q1. This design is for a high-brightness LED and features a wide input voltage, PWM dimming, and an analog dimming capability.

The design has a switching frequency of 125 kHz and an input voltage of 5.5 to 65 V. Electrical performance specifications are:

Fsw = 125 kHz
Vin = 5.5 to 65 Vdc
Vo = Vled = 22 V
Io = 1000 mA

This is all the information needed to proceed to the Coilcraft DC-DC Optimizer tool. The first step is to identify Buck as the driver circuit topology.

Table 1. Typical White LEDs

Company	Part Number	Vf (V)	Io (mA)	Color	Url
Nichia	NJSW170C	3.0	350	White	www.nichia.com
Osram Opto	KW DPLS31.SB	3.05	120	White	www.osram.com
Everlight	A09K-C71501H-AM	3.1	150	Cool White	www.everlight.com
Samsung	SPMWHT346EA3	3.5	140	White	www.samsung.com/led/
Seoul Semiconductor	SZ8-Y11-W0	2.8	150	White	www.seoulsemicon.com
Cree	JE2835 3V	3.0	150	White	www.cree.com

The second step requires inputting the operating parameters: Vin, Vout, Iout, switching frequency and the selection of the allowed peak-peak ripple current.

Note the input voltage as well as the output current and voltage are specified as part of the design requirement. The switching frequency may represent some design freedom if a driver IC is not yet selected, but generally the only degree of freedom in selecting the inductor value is the amount of ripple current to be allowed.

As the default setting, the DC-DC Optimizer tool calculates the ripple current for each inductor in the tool. As an option, a specific ripple percentage can be entered into the tool. In this example, the design uses a 1 Amp solution with 45% peak-peak inductor ripple current.

From these inputs, the Coilcraft DC-DC Optimizer tool calculates the resulting ripple current for each inductor in the tool within a range of the entered ripple current.

With multiple results, the user may optimize the inductor selection based on criteria specific to the application. The tool allows a quick sort of the results by user-selected parameters. For example, for a handheld mobile device or backlight display, component height may be the most important criterion.

If extra margin in the current rating to prevent inductor saturation is preferred, sorting by Isat is recommended.

More importantly, you can sort by total loss (DC loss + AC loss) to select an inductor that provides the best power efficiency for your application.

The Coilcraft DC-DC Optimizer tool features the flexibility to help the user optimize the inductor selection based on the criteria most important to that application.

Conclusion

LED lighting is a growing and exciting application area and Coilcraft design tools can guide the designer quickly and easily to inductors best suited to a variety of applications.

Doc 732

Selecting Inductors to Drive LEDs

Application Design Example

Buck Converter Example

Conclusion

Questions or Concerns?

General Applications

Handling and Processing

RF Inductors

Power Conversion

EMI/RFI Filtering

Special Applications

Warehouses

Language settings

Currency settings

Selecting Inductors to Drive LEDs

Application Design Example

Buck Converter Example

Conclusion

Questions or Concerns?

General Applications

Handling and Processing

RF Inductors

Power Conversion

EMI/RFI Filtering

Special Applications

Warning