|作者：TI 文章来源：TI 点击数： 更新时间：2015-3-25|
The UCC28730 isolated-flyback power supply controller provides Constant-Voltage (CV) and Constant-Current (CC) output regulation without the use of an optical coupler, and signal detection to improve transient response to large load steps. A minimum switching frequency of 30 Hz facilitates achieving less than 5 mW of no-load power. This device processes information from the primary power switch and an auxiliary flyback winding for precise control of output voltage and current. The monitoring works with a secondary-side alarm device such as the UCC24650 to deliver rapid response to heavy load steps using minimal output capacitance.
An internal 700-V start-up switch, dynamically- controlled operating states and a tailored modulation profile support ultra-low stand-by power without sacrificing start-up time or output transient response. Control algorithms in the UCC28730 allow operating efficiencies to meet or exceed applicable standards. Discontinuous conduction mode (DCM) operation with valley-switching reduces switching losses. Modulation of the switching frequency and primary current peak amplitude (FM and AM) keeps the conversion efficiency high across the entire load and line ranges.
Enables (<5 mW) Standby Consumption
Smart Detection Enables Smallest Output Capacitance
Primary-Side Regulation (PSR) Eliminates Opto-coupler
±5% Voltage Regulation and Current Regulation Across Line and Load
700-V Start-up Switch
83-kHz Maximum Switching Frequency Enables Low Stand-by Power Charger Designs
Resonant-Ring Valley-Switching Operation for Highest Overall Efficiency
Frequency-Dither to Ease EMI Compliance
Clamped Gate-Drive Output for MOSFET
Over-Voltage, Low-Line, and Over-Current Protection Functions
Programmable Cable Compensation
Adapters and Chargers for Smart Phones, Tablets, and Other Consumer Electronics
TV and Monitor Power Supplies
SMPS for Home Appliances and Industrial Automation
Standby and Auxiliary Power Supplies
This evaluation module uses the UCC28730 Constant-Voltage, Constant-Current Flyback Controller withPSR and Wake-Up Monitoring with the UCC24650 200-V Wake-Up Monitor for Fast Transient PSR in a10-W converter to provide 2 A of constant charge current. The input accepts a voltage range of 85 VAC to265 VAC. The output is designed for 5 V when in constant voltage mode and will deliver 2 A of constantcurrent down to an output voltage of less than 2 V.
Depending upon the operating conditions, the control law algorithm will modulate the switching frequencyor the peak primary current to satisfy the power transfer requirements. As the load is increased from zero,the converter will transition through a frequency modulation (FM) mode where the peak primary current isheld constant at one-third of its full-load peak value as the switching frequency increases from a minimumvalue to maintain energy transfer up to 28 kHz. When the load is increased to the level at which theswitching frequency reaches 28 kHz, the controller will keep the switching frequency fixed and modulatethe amplitude of peak primary current, increasing it from one-third its peak value up to its maximum fullload peak current value; this area of operation is referred to as the amplitude modulation (AM) range.
Further increase in load demand will transition the controller into another frequency modulation modewhere the peak primary current is constant at its maximum designed value and the switching frequency isincreased, as needed, up to the controller’s maximum 83 kHz switching frequency.
Using PSR, the output voltage is indirectly sensed on the auxiliary winding at the end of the transfer ofstored transformer energy to the secondary to maintain a tightly regulated output. The Wake-Upmonitoring feature operates in conjunction with the secondary-side UCC24650 to allow light-load and noloadswitching frequencies to approach 32 Hz, minimizing no-load power consumption to less than 5 mW,yet provide a fast dynamic response to load transients without requiring large output capacitance. Thecontroller will further enhance its efficient operation with valley switching. The UCC28730 also usesdithering of the gate drive which helps to ease EMI compliance.
This user’s guide provides the schematic, component list, assembly drawing, art work, and test set upnecessary to evaluate the UCC28730 and UCC24650 in a typical off-line converter application.
• AC input range 85 VAC to 265 VAC
• DC output of 5 V, 2 A
• No-load stand-by power consumption less than 5 mW (“Zero-Power”)
• Wake-up detection for fast dynamic response
• Primary-side regulation eliminates opto-coupler
• ±5% output voltage regulation
• ±5% output current regulation
• Average efficiency > 83%; exceeds Level VI and CoC Tier 2 specifications, effective 2016
• Output overcurrent and short circuit protection
• Output overvoltage protection
• Input brown-out protection
• Auto re-start on fault
• Resonant ring valley switching operation for highest overall efficiency
• Frequency dither
• Internal 700-V start-up switch to start up the supply directly from the bulk rail
• 10% efficiency > 80%; complies with CoC Tier 2 specification
• Secondary-side synchronous rectification driven by UCC24610
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