Onsemi NCL30125

Description

This user’s manual provides elementary information about a two−switch forward converter built with the NCL30125 operated in current−mode control. This controller offers many features to build an energy efficient converter with all the needed protections like cycle−by−cycle current limit with a 500−mV sense voltage, over temperature protection with a dedicated NTC pin and brown−out feature. In addition to the low side MSOFET drive, the controller integrates also a high−side section to drive the floating N−channel power MOSFET. Dedicated pins are available to adjust the switching frequency (RT pin – pin 6) or the soft−start duration (SS pin – pin 7). Finally, a high−voltage current source with Dynamic−Self Supply (DSS) is embedded to quickly start the power supply and maintain the Vcc voltage in light load or standby. The primary−side section drives a transformer whose primary inductance is 3 mH. The energy accumulated in this inductance is sending back to the bulk capacitor thanks to the freewheel components. One of the classical freewheel diode has been replaced by a MOSFET Q3 driven by the controller in order to refresh the bootstrap capacitor. The current is sensed via a 83−m resistance. The switching frequency of 100 kHz and the soft−start duration are set by two individual components (R8 for fSW and C5 for SS). The power stage is made of two switching N−channel transistors Q1 and Q2. These two transistors are switched in same time and seen the input voltage as maximum. In the secondary side, D13 and D15 constitute Rectifier and Freewheel part. The regulation is ensured by a TL431.

Features

• Two−Switch topology current mode control
• A simple control circuit without a driver transformer
• Rated Output power: 300 W
• Standby power: <0.3 W in Universal AC input voltage
• Full load Efficiency: >88% @ at board end, 230 Vac input
• Completed protection: OCP,OVP
• Brown−out protection
• Switching frequency: ~100 kHz

Typical applications

• Lighting

More information

• IC product information