Driver ICs for LED Lighting Strips

LED driver ICs are current-controlled regulators that provide biasing current required to activate single LEDs, an LED strip, or multiple LED strips. LEDs emit light when required biasing currents activate forward voltage of the part. Drivers typically drive multiple LEDs situated in either series, parallel, or series-parallel configurations. The color of the light emitted by LEDs is determined by the material used to make the part. Common colors are red, amber, yellow, green, blue, and white.

Color intensity of the LEDs is controlled with biasing provided by the LED driver ICs. The drivers include options for external biasing to increase, or decrease, brightness in addition to PWM circuits for dynamic brightness control. Some drivers integrate PWM with internal registers while others require interface circuits to controllers for application of PWMs to the LED strips on the driver.

Driver ICs are used in a variety of LED lighting applications. The drivers may provide current for one LED or for a string of LEDs. The LED driver ICs provide nominal current biasing within the IC, with the option for providing an external resistor to change the bias point. Changing the bias point either increases or decreases constant current through the LEDs. Dynamic brightness control may be added with PWM circuits. Simple drivers require external PWM circuits while more sophisticated driver designs incorporate internal registers able to apply PWMs for brightness control.

LED lighting strips are driven by driver ICs

Parameters to Consider When Selecting an LED Driver IC

Consider forward voltages of each LED within the strip when using driver ICs to supply one or more strips. Stacking LEDs in series on a strip can build voltages that exceed your source from the driver IC. If this is the case, choosing a driver IC with integrated boost regulator resolves sourcing for biasing. Boosting source voltage holds up the power requirement to drive the LEDs within drooping.

Also keep in mind variations within the material when putting LED strips in parallel. Slight differences in the material can change the overall forward voltage activation resulting in more current passing through one of the strips in the structure. This could lead to reliability issues. It can also lead to brightness inconsistencies in your display. Look for driver ICs that provide low cost solutions for providing current matching between strings.

The following parts provide options for stringing LED strips in either series or parallel configurations. The first two provide current control for one LED strip with the option of putting two driver ICs in parallel to source additional current for LED strips that require bias currents over 65 or 100mA. The third part is specifically designed to provide backlight for LCD displays and incorporates internal registers for PWM brightness control. Get creative with your lighting and have fun with the following options!

Diodes Inc. BCR402UW6-7 Constant Current Regulator

This is an IC designed to drive an LED strip. It is a constant current regulator (CCR) containing biasing within the IC for nominal current of 20mA. Adjustment to the current source is possible with an external resistor. Even more current is possible by placing two BCR402UW6 ICs side by side. For dimming control, external biasing and a microcontroller to provides PWM functionality.

Found on page 6 in Diodes Inc. BCR402UW6-7 datasheet

The BCR402U monolithically integrates a transistor, diodes and resistors to function as a Constant Current Regulator (CCR) for LED driving. The device regulates a preset 20mA nominal that can be adjusted with an external resistor up to 100mA. It is designed for driving LEDs in strings and will reduce current at increasing temperatures to self-protect. Operating as a series linear CCR for LED string current control, it can be used in applications with supply voltages up to 40V.

This part is suitable for use in emergency lighting, signage, advertising, decorative and architectural lighting.

Infineon BCR402UE6327HTSA1 LED Driver

This is an IC developed for use as an LED driver with nominal currents designed to 20mA. Biasing up to 65mA is possible using an external resistor. The part may be operated with up to 40V source voltage. It may be placed in parallel alongside another BCR402UE6327HTSA1 to double current sourcing. In addition, adding biasing to a microcontroller allows dimming via PWM control.

The BCR 402UE6327 is a cost efficient LED driver to drive low power LEDs. The advantages towards resistor biasing are:

• Homogenous light output despite varying forward voltages in different LED strings
• Homogenous light output of LEDs despite voltage drop across long supply lines
• Homogenous light output independent from supply voltage variations
• Longer lifetime of the LEDs due to reduced output current at higher temperatures (negative thermal coefficient) The advantages towards discrete solutions are:
• Lower assembly cost
• Smaller form factor
• High reliability due to less soldering joints
• Higher output current accuracy due to pretested LED drivers Dimming is possible by using an external digital transistor at the ground pin.

Found on page 14 of Infineon BCR402UE6327HTSA1 datasheet

This part is suitable for automotive applications carrying AEC Q101 qualification. It is suitable in advertising for channel letters, and for decorative lighting using LED strips. It can be used for transportation on aircraft, train, or ship illumination. It is also suitable for home appliances and for special lighting.

ST Microelectronics LED7708 LED Driver With Boost Controller

This IC offered by ST Microelectronics, the LED7708, is designed for use as a CCR able to drive up to four channels of LED strips. It has internal registers making it programmable from a host controller. It is also possible to adjust the nominal 20mA current to each channel with external resistor biasing to provide up to 85mA per channel. Its operating voltage ranges from 3.6V to 36V.

Found on page 29 of STMicroelectronics LED7708TR datasheet

The LED7708 is an LED driver that integrates a boost controller, sixteen current generators and a 4-wire serial interface. It has been specifically designed for driving the LED backlight in medium to large LCD panels. The device is controlled by a 4-wire serial interface and can operate both as standalone driver and as master driver in conjunction with other slave devices. Basic and advanced dimming functions are supported in order to meet different application requirements. Regardless of the dimming control technique, the LED7708 can optimize the power dissipation by controlling the output voltage of the boost converter. Two internal linear regulators derive the device supply (3.3V) and the gate driver supply (5V) from a single power rail.

This part is designed specifically for use in medium to large LCD panels to drive the LED backlight. It can be used either the standalone or master driver for multiple LED strings.

LED driver ICs find applications in many industrial and consumer devices where LED lighting is incorporated into the design. LEDs are current-controlled devices with forward voltages in the neighborhood of 1.2V to 3.6V. Placing LEDs serially in a string results in forward voltages adding and LED driver ICs must provide source voltages to include LED string demands. Some LED driver ICs provide boost regulators to generate the necessary holdup voltages for LED strings.

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