基于UCC28600的准谐振反向控制器

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基于UCC28600的准谐振反向控制器

　　1 Features

　　Green-Mode Controller With Advanced Energy Saving Features

　　Quasi-Resonant Mode Operation for Reduced EMI and Low Switching Losses (Low-Voltage Valley Switching)

　　Low Standby Current for Minimum System No-Load Power Consumption

　　Low Start-up Current: 25-μA Maximum

　　Programmable Line and Load Over-Voltage Protection

　　Internal Over-Temperature Protection

　　Current Limit Protection

　　Cycle-by-Cycle Power Limit

　　Primary-Side Over-Current Hiccup Restart Mode

　　1-A Sink, –0.75-A Source TrueDrive™ Gate Drive Output

　　Programmable Soft-Start

　　Green-Mode Status Pin (PFC Disable Function)

　　2 Applications

　　Bias Supplies for LCD-Monitors, LCD-TV, PDP-TV, and Set Top Boxes

　　AC-to-DC Adapters and Off-Line Battery Chargers

　　Energy Efficient Power Supplies up to 200 W

　　3 Description

　　The UCC28600 is a PWM controller with advanced energy features to meet stringent world-wide energy efficiency requirements.

　　UCC28600 integrates built-in advanced energy saving features with high-level protection features to provide cost-effective solutions for energy-efficient power supplies. UCC28600 incorporates frequency fold-back and green-mode operation to reduce the switching losses at light-load and no-load conditions.

　　UCC28600 is available in the 8-pin SOIC package. Operating junction temperature range is –40°C to +105°C.

　　The UCC28600 Design Calculator, (SLVC104), located in the Tools and Software section of the UCC28600 product folder, provides a user-interactive iterative process for selecting recommended component values for an optimal design.

　　The UCC28600 is a flyback power supply controller that operates in different operating modes, modulating the peak primary current and/or the switching frequency, depending upon the line and load conditions. The controller will operate in burst mode operation, or green mode (GM) driving the primary side MOSFET with packets of

　　40-kHz pulses, at fixed peak primary current for light-load conditions. As the load increases, the 40-kHz switching will become consistent and the controller will transition to frequency fold-back mode (FFM), where the peak primary current is held constant and the switching frequency is modulated from 40 kHz up to 130 kHz, in order to maintain regulation. At higher loads, the UCC28600 will operate in either DCM, where the peak primary current is modulated but the switching frequency is maintained at its maximum value, or quasi-resonant mode (QRM), where the switching frequency and the peak primary current are both modulated in order to maintain regulation.

　　The UCC28600 is a multi-mode controller, as illustrated in Figure 5 and Figure 12. The mode of operation depends upon line and load conditions. Under all modes of operation, the UCC28600 terminates the OUT = HI signal based on the switch current. Thus, the UCC28600 always operates in current mode control so that the power MOSFET current is always limited.

Under normal operating conditions, the FB pin commands the operating mode of the UCC28600 at the voltage thresholds shown in the control flow chart, Figure 11. Soft-start and fault responses are the exception. During soft start, the converter switching frequency is fixed at 40 kHz and FB is set to 5V. The soft-start mode is latched-OFF when VSS becomes greater than VFB for the first time after UVLOON. The soft-start state cannot be recovered until after passing UVLOOFF, and then, UVLOON.

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　　From 100% to approximately 30% full rated power the UCC28600 controls the converter in quasi-resonant mode (QRM) or discontinuous conduction mode (DCM), where DCM operation is at the clamped maximum switching frequency (130 kHz). For loads that are between approximately 30% and 10% full rated power, the converter operates in frequency foldback mode (FFM), where the peak switch current is constant and the output voltage is regulated by modulating the switching frequency for a given and fixed VIN. Effectively, operation in FFM results in the application of constant volt-seconds to the flyback transformer each switching cycle. Voltage regulation in FFM is achieved by varying the switching frequency in the range from 130 kHz to 40 kHz. For extremely light loads (below approximately 10% full rated power), the converter is controlled using bursts of 40-kHz pulses.