LED Driver Solutions(1)

The LED drive circuit is a kind of power converter circuit providing a constant current. The LED drive circuit should contain at least a voltage detection circuit and a current switch circuit.

When the voltage detection circuit detects different voltage grade of the power supply, it will send a signal to current switch circuit, and then current switch circuit will be automatically activated. Using predetermined current value to adjust the electrical set of LED, thus can effectively light up LED as much as possible.

Linear actuator

Linear regulators can provide a simple method to generate constant current through connecting a current sampling resistance between the voltage stabilizer output and ground point. The regulator’s constant output voltage generates the constant current through the feedback resistance. Power supply reference voltage and current sampling resistance determined the LED current. Linear regulators usually are used to drive the low power LED, such as the backlight of PDA this portable devices. The typical current value in these LED is in 15 mA to 25 mA, Vf is in 3.0 V to 3.4 V. If linear actuator is used for power supply of multi LED, these LEDS should be in series to insure the same current through all LEDs, which lead to shine amount roughly equal.

The advantages of the linear actuator is plan cost and electromagnetic interference is low, because linear regulators just need to set several resistances around the drive IC, and it will not use switch components. Due to the linear actuator needs to output high voltage to provide LED current, so the shortcomings of the scheme is low efficiency, namely the ratio of the LED voltage and power supply voltage is low. Linear regulators major limitation is the power supply voltage is always higher than the LED voltage, and the linear voltage source can’t improve output voltage, it will only lower voltage to a certain extent. This kind of low efficiency can cause fever problem.

Switch driver

For high current applications in a wide range of input, such as mentioned above, the simple drive plan can produce higher calorific value and low efficiency. Switch driver with constant current output is the first choice of driving high power LED. The driver is usually used in switch control to series inductance and LED load or parallel capacitance and LED the power supply voltage. The inductor or capacitor is used to save electric energy when the switch opened; and then provide current for LED when the switch is closed. Different with linear actuator, switch driver can be configured to realize the function of voltage buck, boost or both them. So obviously switch driver allows LED working in a wider range of input voltage. In addition to the current adjustment function with constant amount of light, they can also limit power loss to the minimum. Beyond doubt is switching voltage regulators is more efficient than linear regulators. However, compared with linear regulators, switch driver has higher costs and need to have careful design for EMI problem. In order to use the appropriate way to drive LED, we need to find the most satisfactory price performance.