NCL30082FLYGEVB ON Semiconductor

NCL30083FLYGEVB, NCL30083BB1GEVB 10 W Passive PFC Flyback and BuckBoost Dimmable LED Driver Evaluation NCL30083FLYGEVB, NCL30083BB1GEVB Demo Board Modifications Since the NCL30082/3 has a wide V range this allows CC The board as shipped contains the NCL30083 to one transformer/inductor design to a > 2:1 change in LED demonstrate the line step dimming function which allows string forward voltage. If it is desired to reduce the output the LEDs to be dimmed in 5 discrete steps by toggling the current, the output power is no longer the limit, but simply AC line (V ) off momentarily. C holds up V while in vccbulk CC the level of the reflected voltage from the auxiliary winding V toggles low switching to the next lower dim level. Since in which is monitored by the built in overvoltage protection of the timing is user controlled by switching on/off the light the V pin. If a higher output voltage at lower current is CC switch the timing window is very wide. Toggling the AC required, the auxiliary winding turns ratio would have to be input in one second is typical. It may take more than modified. 20 seconds of AC off to reset the IC, at which time when The input capacitor network uses a valley fill PFC to turned on again it return to the 100% state. By removing the achieve a power factor of > 0.8 to easily meet ENERGY C the step dimming function is effectively disabled so STAR input power factor requirements. If compliance vccbulk the performance of the current control is just like the with EN61000-3-2 Class C is required, the input capacitor NCL300082. It is also possible with this board to replace the network can be easily modified and simplified to one NCL30083 with an NCL30082 to evaluate the analog/ capacitor, this is discussed in the appendix. dimming control. Constant Current Control Architecture Introduction The value of R sets the final output current value in sense Figure 4 portrays the primary and secondary current of a conjunction with R which is for fine adjustment. The trim fly-back converter in discontinuous conduction mode nature of the primary side loop control makes the current (DCM). Figure 3 shows the basic circuit of a fly-back adjustment somewhat iterative because several circuit converter. parameters affect the output current setting. It is relatively easy by changing R to increase the output of the sense evaluation board as long as the output power limit is considered. V Transformer bulk L leak N sp C R clp clp V out . + L p . Clamping Network C lump DRV R sense Figure 3. Basic Flyback Converter Schematic During the on-time of the MOSFET, the bulk voltage V bulk N V V sp out f is applied to the magnetizing and leakage inductors L and p The output diode current increase is limited by the leakage L . The current ramps up. leak inductor. As a consequence, the secondary peak current is When the MOSFET is turned-off, the inductor current reduced: first charges C . The output diode is off until the voltage lump across L reverses and reaches: p