Onsemi NCP4305 | Demoboard NCP4305FBDAPGEVB

Description

The presented design demonstrates a switching mode AC/DCadapter with high efficiency through whole load range including noload consumption. The design utilizes a primary controllerNCP1249C/D, secondary side CVCC and off-mode controllerNCP4354A and last but not least synchronous rectification controllerNCP4305.The NCP1249 is fixed frequency current mode flyback controllerfeaturing a peak power excursion, high-voltage start-up, off-mode andX2 capacitor discharging feature. Secondary side controllerNCP4354A features two OTAs that are used to provide constantvoltage and constant current regulator, very light load conditiondetection, off-mode control and indication LED driver. NCP4354Acommunicates with primary controller featuring off-mode throughregulation optocoupler. Secondary side synchronous controllerNCP4305 is used to control a MOSFET transistor that is used in placeof a rectification diode on the secondary side.The NCP4035 controller turns the synchronous rectifier transistoron in time for current to flow from the transformer to adapter output.Since the voltage drop on the transistor is lower than the voltage dropover a diode this leads to a higher overall efficiency adapter. TheNCP4305 monitors the voltage across the synchronous rectificationtransistor and according to its magnitude and value; it turns thetransistor on and off. This controller also includes feature light loaddetection that is used to modulate the driver output for smoothtransitions between medium and light loads. In very light loads thelight load detection feature will disable the controller to eliminateswitching losses. ON Semiconductor’s newest synchronous rectifierhas a 4 A drive and an 8 A sink driver. The strong and robust driver ofthe NCP4305 allows for a very fast, controlled and accurate turn onand turn off to maximize conduction period. The strong sink on theNCP4305 allows this controller to operate in CCM. To furtherimprove efficiency the NCP4305 has incorporated an ultra fast trigger.The trigger pin can be used to help reduce cross conduction, andimprove efficiency, during CCM. Information about primary sideturn-on can be transferred to NCP4305’s TRIG pin on the secondaryside that immediately turns-off the SR transistor.

Features

• Synchronous Rectification
• Constant Voltage Constant Current Regulation (CCCV)
• Very Low Input Power at Light and No Load
• High Efficiency Across the Entire Load Range
• Overpower Protection
• Universal Mains Operation

More information

• Datasheet
• IC product information