Study On LED Driver Power Supply Based On Cuk PFC Converter

With the rapid development of Light Emitting Diode(LED)in computer display backlight,home lighting,stage lighting and other application technologies,single-channel constant current output and multi-channel constant current output LED driver power supply have been widely applied in recent years.The LED is a low-voltage DC device that is driven by a constant current and has a low forward voltage.Therefore,the AC input voltage of the grid cannot be directly used to drive the LED,and the switching converter is used to convert the grid power.The IEC61000-3-2 regulations impose restrictions on the harmonic currents injected into the grid by AC-DC switching converters to reduce harmonic pollution to the grid.Therefore,a power factor correction(PFC)converter needs to be added to the input of the switching converter.Based on the the improved Cuk PFC converter,this dissertation aims to study LED driving power sources with high power factor,low cost and low output current ripple.The traditional LED driver with PFC function only uses the one-stage circuit to realize the adjustment of PFC and output current at the same time.However,due to the imbalance between the pulsating input power and the constant output power,the output current will have great twice line frequency ripple.The twice line frequency ripple will cause the LED to strobe,which will cause certain damage to human health.The traditional two-stage structure is composed of two-stage converter cascade,the front stage realizes the power factor correction function,and the latter stage realizes the adjustment of the output current.This scheme will result in complicated circuit structure and high cost.This paper proposes a single-output LED driver power supply structure based on Cuk PFC converter.The structure belongs to a single-stage structure,and its front-end loop is similar to Boost converter,which can be used to implement power factor correction function,while the latter circuit is similar to the Buck converter which realizes DC-DC conversion to accurately adjust the output current,which can solve the problem that the output current of the conventional first-level scheme has twice the power frequency ripple and the two-stage cascade structure has high cost and complicated circuit.Due to the current packaging technology and heat dissipation limitations,the luminous flux of a single LED does not meet the growing lighting demand,and multiple strings of LEDs must be connected in parallel.The multi-string LED parallel connection will inevitably lead to the current sharing problem between the LED strings.This paper compares the advantages and disadvantages of the active and passive multi-output LED current sharing scheme.In order to achieve stable and reliable LED color temperature adjustment and dimming,the traditional scheme uses a two-stage cascade structure,the front stage realizes the power factor correction function,and the subsequent stage cascades multiple DC-DC converters to achieve constant output current regulation.Although the scheme can effectively and reliably realize LED color adjustment and dimming color adjustment,multiple controllers and multiple magnetic components are required,which increases the size and cost of the system.In the third chapter of this paper,the LED driving power supply based on the dual-channel constant current output single-stage Cuk PFC converter and its control strategy are implemented to realize the LED color temperature adjustment.The conditions of the input and output inductors operating in the discontinuous mode,the storage capacitor voltage,and power factor are derived in detail.By utilizing the inductor multiplexing technique,power factor correction function and precise independent adjustment of the two output currents are achieved simultaneously.Compared with the traditional two-stage output power system with two levels of cascade structure,the number of inductors and controllers is reduced,the cost is reduced,and the efficiency of the system is improved.Based on the dual-channel constant current output,the LED driving power supply based on the three-channel constant current output single-stage Cuk PFC converter and its control strategy are further studied to realize the dimming and color grading function of the LED.Only one controller is required to achieve both PFC function and stable regulation of three output currents,which greatly reduces the size and cost of the system.The conditions of the input inductor operating in the discontinuous mode,the expressions of the intermediate storage capacitor voltage,and power factor are analyzed in detail.The simulation and experimental results show that the LED driver power supply based on the three-channel constant current output single-stage Cuk PFC converter can simultaneously realize the power factor correction function and the independent adjustment of the three output currents,and can be applied to the LED dimming adjustment.In the applications of LED dimming and color adjustment,a stable and reliable dimming function is realized.Finally,the corresponding simulation and experimental prototype are built for verification.