FlexBlock Buck-Boost DC LED Driver

Description

The LuxDrive™ A011 series FlexBlock™ is a dual-mode boosting LED power solution for driving high-brightness LED(s). The default constant current output mode is 'Buck-Boost', but with a simple change in wiring this driver can run in 'Boost-Only' mode as well. More information is listed below and within the downloadable documentation, but for a complete write-up on the FlexBlock LED driver here is a link within our site: Published September 5th, 2014 titled 'The Buck-Boosting FlexBlock LED Driver'.

Buck-Boost Mode

In Buck-Boost (standard) mode the driver can handle LED loads that are above, below, or the same voltage as the power-supply.

Boost-Only

In Boost-Only mode it can output up to 48vdc from as little as 10Vdc.

Control & Dimming

A fast response current sensing circuit permits the unit to be used in applications where flashing or strobing of the LED(s) is required; and a 0-10V dimming input provides a convenient method to control the brightness of the LEDs.

Form Factor & Size

The driver is extremely low profile, fully potted and comes with six inch 18AWG colored leads, making installation into tight spaces fast and easy.

Constant Current Output

The output of the FlexBlock LED driver is available in 350mA, 500mA or 700mA constant current.

Technical Documentation

Product Selection

Absolute Maximum Ratings

Full Documentation

Application Information: The FlexBlockTM High Output LED Power Module is a high-efficiency dc to dc converter that delivers a fixed output current by varying the output voltage as required to maintain the specified current. Because the forward voltage of LEDs can change based on several environmental factors as well as the age of the LED, it is important to use this type of driver in an LED system. A fast response current-sensing circuit permits the unit to be used in applications where flashing or pulsing of the LEDs is required. Several options are available allowing for use with many types of LEDs and in a variety of operating modes.

Fixed Current Drive: When the dimming wires (purple/gray) are left unconnected, the FlexBlock is designed to supply its rated current to one or more LED junctions. For example, a 700mA rated unit will drive up to five white 700mA LEDs connected in series at 12VDC. See figure 2 and figure 3.

When wired in the default configuration, as marked on the top of the unit, the A011 FlexBlock is in Buck-Boost mode. This is the most flexible mode as it allows the input voltage to be below, the same, or above the output voltage. This mode is recommended for loads with up to 6 LEDs in series.

A second, more efficient wiring option puts the A011 FlexBlock in boost-only mode. In this mode, the LED+ output is not used, and the positive end of the LED load is instead connected to Vin+. This is shown in Figure 11. It is extremely important that Vin < Vout under all conditions (LED forward voltages shrink slightly as the LEDs warm up and as the LEDs are dimmed). If white LEDs are going to be dimmed, it is recommended that Vin be less than (2V * #LEDs in series) to make sure the LEDs can be fully extinguished. This is due to the fact that many LEDs will begin to light up at around 2.5V, at a reduced current, even when rated at 3.0Vf.

Figure 10 shows a 700mA unit driving multiple LEDs. Note that parallel strings of LEDs can be driven directly with no additional circuitry required to insure current sharing. The nature of the LEDs themselves will provide sufficient current sharing if the parallel strings comprise three or more junctions each, and are identical in length.

Adjustable Current - External Control - "V" Model: Figures 14 and 15 show the ease of dimming the A019 FlexBlockTM High Output LED Power Module. Figure 14 shows the simplest dimming configuration using a 20K Ohm potentiometer. This gives a 0-100% range of dimming. If multiple A019 modules are to be dimmed with a single potentiometer, the value of the potentiometer should be approximately (20KΩ/N) where N is the number of modules.

Figure 15 shows a 0-10V wall dimmer, such as LEDdynamics A019 Low Voltage Dimming Control, being used to control the LED brightness. This is the preferred choice for dimming multiple units, as the 0-10V dimmer can handle several drivers. The 0-10V input can also be supplied by a commercial lighting controller that has current-sinking 0-10V outputs, allowing the integration of LEDs with other forms of lighting in large automated systems.

For large systems where several distant FlexBlock modules will be dimmed together, it is important to use a heavier gauge wire (such as 18AWG) to run the DIM lines in a star wiring pattern (where each module has a run all the way back to the dimmer). This will help to negate any voltage drops along the DIM wires that could cause some lamps to dim differently than others.

For more advanced control, the 0-10V input can be Pulse Width Modulated (PWM). Figure 18 shows how interfacing with a micro-controller can easily be accomplished with a 2N3904 or equivalent transistor. A PWM frequency of 200Hz is recommended. This configuration can also be used to strobe or pulse the LEDs with a TTL or CMOS logic signal.

In addition to the configurations described above, the FlexBlock may also be driven by a D to A converter. The D/A converter must be able to sink at least 1ma of current from the 0-10V input of the FlexBlock. If the D/A converter cannot sink current, a voltage follower with an open collector output should be used between the D/A converter and the 0-10V input.

If the dimming control circuit used with the FlexBlock has the potential to exceed 10V, current into the DIM input needs to be limited to 10mA or less. See figure 8.

External On/Off Control: Where a manual on/off control is desired, the potentiometer in Figure 14 may be replaced by a push-button or toggle switch. The output current will be zero and the input current will drop to the quiescent level when the switch is closed. Figures 16 and 17 show external dimming control combined with on/off control.

Thermal Management: The FlexBlock can run many LED load configurations with no additional heat sinking in an ambient of 25°C. In situations with elevated ambient temperatures, such as those that might be experienced inside an enclosed fixture, additional heat sinking may be required. If the temperature of the driver (as measured at the T marking on the label) exceeds 60°C, additional heat sinking is recommended. If the temperature of the driver exceeds 80°C, additional heat sinking is required.

The best surface for removing heat form the FlexBlock is the back side (opposite the labeled side). The module can be attached to a heat sink with thermal grease and a mounting bracket that presses the unit firmly against the heat sink, or with double-sided tape that provides both the thermal path and mechanical mounting. When using tape (such as 3M F9469PC, a Very High Bond (VHB) tape suitable for permanent mounting), using a thinner variety (0.005" thick or less) will aid in getting the heat through the tape and to the heat sink. Care should be taken when positioning the FlexBlock module with VHB tape as the high bond strength makes removing or re-positioning the module very difficult.

If the FlexBlock becomes too hot during use, it will reduce the output current to limit the power dissipation. If the temperature continues to rise, the driver will turn off until the temperature drops to a safe level.

Connections: In all cases, the LEDs being driven should be located as close to the FlexBlock LED output as possible. 18AWG wire should be adequate for most wiring, but a heavier gauge should be considered when long leads are required

The power input wires should also be kept short. Where the power source is located several feet from the unit, a 100µF or larger, 50V capacitor may be required across the input terminals as shown in Figure 20.

Note: The above are product highlights and not the complete manufacturers datasheet. Please view the .pdf for complete specifications.

Full Documentation

FlexBlock Documentation