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說明

The UCC2850x family provides all of the control functions necessary for an active power-factor-corrected preregulator and a second-stage dc-to-dc converter. The controller achieves near-unity power factor by shaping the ac input line current waveform to correspond to the ac input-line voltage using average current-mode control. The dc-to-dc converter uses peak current-mode control to perform the step-down power conversion.

The PFC stage is leading-edge modulated while the second stage is trailing-edge synchronized to allow for minimum overlap between the boost and PWM switches. This reduces ripple current in the bulk-output capacitor.In order to operate with over three-to-one range of input-line voltages, a line feedforward (V_FF) is used to keep input power constant with varying input voltage.

特性

• Combines PFC and Downstream Converter Controls
• Controls Boost Preregulator to Near-Unity Power Factor
• Accurate Power Limiting
• Improved Feedforward Line Regulation
• Peak Current-Mode Control in Second Stage
• Programmable Oscillator
• Leading-Edge/Trailing-Edge Modulation for Reduced Output Ripple
• Low Start-up Supply Current
• Synchronized Second Stage Start-Up, with Programmable Soft-start
• Programmable Second Stage Shutdown