Parallel design experience in LED driver design

LEDs do not have the same characteristics due to their VF characteristics. Some VF values ​​also change with temperature and current, and are generally not suitable for parallel design. However, in some cases, it is necessary to solve the problem of multiple LED driving costs in parallel. These designs can be used for reference.

Note that the VF value binning is required. The LED of the same VF value should be used on the same product as much as possible. The product can ensure that the error current is within 1 mA and the LED is in a working constant current state.

The integrated triode can keep the LED currents consistent. The triodes produced under the same temperature conditions and the same process conditions can ensure that each current is basically the same. The constant current part can be designed under the condition that the requirement is not very high, and the stable voltage or the stable PWM value drives the stabilized triode bias to achieve a basic constant current.

A high-precision IC is used as a constant current reference source, and R can set the IC output current. Once the R resistance value is determined, a fixed resistor can be used instead. The use of multi-triode integrated devices reduces the number of ICs used, thereby reducing the cost of designing products.

Linear high-power LED constant current output can be used in parallel. In product design, we often can't find a driver IC with a large current. Generally, 2A or above is rare, and the nominal 2A IC may not be used at all. The MOS tube is external because of the IC process cost greater than 1A, and the external MOS tube has complicated wiring and reduced reliability. Parallel use is an effective design approach.

The DD312 parallel reference design directly drives three 6W LEDs. Enabling PWM control signals requires proper isolation to avoid mutual interference and drive capability issues. The EN enable voltage must meet the specifications and do not damage the EN pin too high. General IC withstand voltage refers to the load and power supply, please do not specify the excitation voltage, please do not exceed the 5V design.

Like this detection, the LED constant current driver IC at one end of the LED can also be driven in parallel. In fact, the IC works alone and finally in parallel. The DC-DC mode works at a higher frequency. It should be noted that the PCB layout avoids crossover design. The respective filtering and bypass capacitors should be close to the IC, and the load current will eventually be met.

Of course, it can be 2 or 3 or more parallel design, but you should remind me to try it!

Editor: China Lighting Network Feng Yaoyuan

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