UTC UC3846 Low Cost Power-Saving Mode PWM Controller for Flyback Converters

The UTC UC3846 is a high-performance current mode PWM controller ideally suited for low standby power and cost-effective off-line flyback converters. Its low VDD startup current ensures reliable startup design, and a large-value resistor can be used in the startup circuit to minimize standby power.

At no-load condition, the IC operates in burst mode for lower standby power and in decreasing frequency for higher conversion efficiency at light load. The PWM switching frequency is programmable externally during normal operation.

Protection Features

The UTC UC3846 includes comprehensive automatic self-recovery protection:

• OCP – Cycle-by-cycle current limiting
• OTP – Over temperature protection
• UVLO – VDD over voltage clamp and under voltage lockout
• Gate-drive output clamped at 15V max to protect the power MOSFET

Advanced Performance

Internal slope compensation improves system stability at high PWM duty cycle. Leading-edge blanking on the current sense (CS) input removes signal glitches, minimizing external component requirements and lowering system cost. Excellent EMI performance is achieved via UTC's proprietary frequency hopping technique combined with soft driver control. Audio noise is eliminated as the switching frequency exceeds 20kHz during operation.

Applications

• Battery chargers
• Power adaptors
• Set-top box power supplies
• Inkjet printers
• Open-frame SMPS

Key Features

• UTC proprietary frequency hopping for improved EMI performance
• Power-saving mode for high light-load efficiency
• Burst mode for minimum standby power
• Dynamic peak current limiting for constant output power
• Built-in synchronized slope compensation
• OTP, OVP, and VDD clamp for higher security
• Programmable PWM frequency
• Gate output voltage clamped at 15V
• Low start-up current
• Cycle-by-cycle current limiting
• Under voltage lockout (UVLO)
• Few external components required

Package: DIP-8 | Manufacturer: Unisonic Technologies Co., Ltd |

 www.unisonic.com.tw