Working with LED Drivers
LED Driver Definition
An LED driver is a device that manages power and controls the current flow for an LED lighting product. LED lighting doesn’t require high voltage, and depending on the application, could even use batteries or solar power. In the HB-LED lighting market, the term driver is usually applied to a device that can accept an input voltage and produce the required voltage. An important factor that affects the choice of a particular driver is the way in which multiple LEDs are actually wired together.
LED Wiring Configurations
Since most commercial applications of HB-LEDs for lighting require multiple LEDs to be connected together to produce the amount of luminous flux (lumens) needed, some consideration must be given as to how to wire them up. The three general wiring configurations are:
- Series – LEDs form a chain, cathode to anode
- Parallel – All the cathodes are connected together and all anodes are connected together
Series/Parallel – LEDs are connected in series to form a chain and then the chains are wired in parallel
LED Driver Topologies
LED driver topology refers to the physical design, layout, and capability of the driver. LED driver topologies vary since an LED driver controls power by stepping it up or down depending on the input voltage and required output for the application. You will notice that the topology terminology used for LED drivers, is the same used in switch mode power supplies and DC-to-DC Converter topologies.
LED driver topologies:
- Buck – Stepping down a higher input voltage to a lower output voltage
- Boost – Stepping up an input voltages to a higher output voltage
- Buck/Boost – Allows the input voltage to vary: It can be greater than and it can be less than or equal to the output voltage
| Boost (Step-up) | Buck (Step-down) |
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Buck-Boost |
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| VOUTVIN > VOUT and VIN VOUT | |
Inductor-based and Charge Pump LED Drivers
Two other terms used to further categorize LED drivers are inductor-based and charge pump drivers.
Inductor-based drivers require an inductor in order to output the higher voltage needed by serial wired LEDs. Although theses drivers are over 90 percent efficient, they can generate EMI and they require a larger package than the charge pump driver.
A charge pump driver uses capacitors to produce 1X, 1.5X, and 2X the input voltage. Its design eliminates the need for the inductor and generates no EMI, but may not be as power efficient as an inductor-based driver.LED Ballast
The term ballast, as used in an LED lighting application, refers to a complete pre-packaged assembly including driver, integrated transformer, and all the associated electronic components and circuitry required to convert and manage power. There are two basic types of ballasts, depending on the input voltage.
AC-to-DC Converter
DC-to-DC Converter
These ballasts/drivers consist of the previously mentioned topologies: Buck, Boost, and Buck-Boost.
