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LED drive power supply topologies


LED drive power supply topologies

AC-DC power LED lighting applications, building blocks, including power conversion diode, switch (FET), inductance and capacitance and resistance, and other discrete components for the performance of their respective functions, the regulator is used to control the pulse width modulation (PWM) power conversion.

Circuit usually transformer-isolated AC-DC power converter includes a flyback, forward, half-bridge topology, see Figure 3, in which the flyback topology power less than 30W, the standard choice for low-power applications, and the half-bridge structure is best suited to provide a higher energy efficiency / power density. Isolation transformer structure, the size of its size with the switching frequency, and the majority of the isolated Using essentially the LED drive “electronic transformer.

DC-DC power LED lighting applications, can be used to operate an LED resistive, linear regulator and switching regulator, the basic application diagram shown in Figure 4. Resistance-type drive mode, adjust the series with the LED current sense resistor to control LED forward current, this drive easy to design, low cost, and there is no problem of electromagnetic compatibility (EMC), the disadvantage is dependent on the voltage, need to be screened (binning) LED, and can lower efficiency.

Linear regulator is also easy to design and EMC problems, also supports the current regulation and over-current protection (FOLDBACK), and the external current set point, the drawback is that the power dissipation, and input voltage should always be higher than the forward voltage , and can efficiency is not high. Switching regulator control switch (FET) on and off, and then control the flow of current through the PWM control module constantly.

Switching regulator with higher energy efficiency, has nothing to do with the voltage can control the brightness is relatively high cost, complexity is higher, and the presence of electromagnetic interference (EMI). LEDDC-DC switching regulator topology common include different types of step-down (Buck), Step-Up (Boost), Buck – Boost (Buck-Boost) or single-ended primary inductance converter (SEPIC).

Which, under all operating conditions, the minimum input voltage is greater than the maximum LED string voltage step-down structure, such as to 24Vdc drive 6 series LED; contrast, the maximum input voltage is less than the minimum output voltage under all operating conditions with l pressure structure, such as the use of LED 12Vdc drive 6 series; range of input voltage and output voltage can be used when there is overlap buck – boost or SEPIC structure, such as using the 12Vdc or 12Vac drive, four series of LED, but this cost and energy efficiency of the structure is not ideal.

AC power directly drive LED’s also a certain degree of development in recent years, its application diagram shown in Figure 5. Ordering LED string in the opposite direction in such a configuration, the work in the half-cycle, and the LED in the line voltage is greater than the forward voltage when conduction. This structure has its advantages, such as to avoid the power loss caused by the AC-DC conversion. However, this structure LED in the low-frequency switch, the enemy eyes may be perceived flicker. In addition, this design also need to add the LED secure it from line surge or transient effects.

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