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UC1548 Folha de dados(PDF) 1 Page - Texas Instruments |
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UC1548 Folha de dados(HTML) 1 Page - Texas Instruments |
1 / 9 page 4/97 BLOCK DIAGRAM • Primary Side Voltage Feed- forward Control of Isolated Power Supplies • Accurate DC Control of Secondary Side Short Circuit Current using Primary Side Average Current Mode Control • Accurate Programmable Maximum Duty Cycle Clamp • Maximum Volt-Second Product Clamp to Prevent Core Saturation • Practical Operation Up to 1MHz • High Current (2A Pk) Totem Pole Output Driver • Wide Bandwidth (8MHz) Current Error Amplifier • Undervoltage Lockout Monitors VCC, VIN and VREF • Output Active Low During UVLO • Low Startup Current (500 µA) The UC3548 family of PWM control ICs uses voltage feed- forward control to regulate the output voltage of isolated power supplies. The UC3548 resides on the primary side and has the necessary features to accurately control sec- ondary side short circuit current with average current mode control techniques. The UC3548 can be used to control a wide variety of converter topologies. In addition to the basic functions required for pulse width modulation, the UC3548 implements a patented technique of sensing secondary current from the primary side in an isolated buck derived converter. A current waveform syn- thesizer monitors switch current and simulates the inductor current downslope so that the complete current waveform can be constructed on the primary side without actual sec- ondary side measurement. This information on the primary side is used by an average current mode control circuit to accurately limit maximum output current. The UC3548 circuitry includes a precision reference, a wide bandwidth error amplifier for average current control, an oscillator to generate the system clock, latching PWM comparator and logic circuits, and a high current output driver. The current error amplifier easily interfaces with an optoisolator from a secondary side voltage sensing circuit. A full featured undervoltage lockout (UVLO) circuit is con- tained in the UC3548. UVLO monitors the supply voltage to the controller (VCC), the reference voltage (VREF), and the input line voltage (VIN). All three must be good before soft start commences. If either VCC or VIN is low, the sup- ply current required by the chip is only 500 µA and the output is actively held low. Two on board protection features set controlled limits to prevent transformer core saturation. Input voltage is moni- tored and pulse width is constrained to limit the maximum volt-second product applied to the transformer. A unique patented technique limits maximum duty cycle within 3% of a user programmed value. These two features allow for more optimal use of trans- formers and switches, resulting in reduced system size and cost. Both patents embodied in the UC3548 belong to Lambda Electronics Incorporated and are licensed for use in appli- cations employing these devices. UC1548 UC2548 UC3548 Primary Side PWM Controller FEATURES DESCRIPTION UDG-95037 Pin numbers refer to 16-pin DIL and SOIC packages only. |
Nº de peça semelhante - UC1548 |
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Descrição semelhante - UC1548 |
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