高级初级侧启动控制器
The advanced primary-side startup controller is a unique solution that provides all the primary-side functions required for a single-ended, isolated, switch-mode power converter incorporating secondary-side PWM control. It is usable with a wide range of secondary control circuits and is especially well suited for systems where sophisticated handling of overload conditions is required.
Secondary-side control assumes that output voltage and current measurements are interfaced directly to an output ground-referenced PWM stage that develops the power switch command for the supply. This digital PWM command can then be transmitted to the primary-side power switch through a simple and low-cost isolating pulse transformer. With secondary-side control, it is much easier to monitor and control the system load with tightly coupled analog control loops. Load-oriented features such as output current sharing and synchronous rectification are implemented more easily.
The UCC3961 provides all the circuitry required on the primary side of a secondary-side controlled power supply. It features a free running 60-kHz to 360-kHz oscillator which is synchronizable to the secondary-side PWM signal and also has the ability to accept start/stop PWM commands from the isolating pulse-edge transformer PET. The use of an extremely small and low-cost pulse transformer allows for higher converter bandwidth. This also eliminates the loop-gain variations due to initial accuracy and aging of an opto-coupler feedback element or the size penalty of a gate transformer. It also includes an undervoltage lockout circuit with 2-V hysteresis, a low-current startup with active low during UVLO, a soft-start capability, a 5-V reference and a high-current power output.
Advanced features of UCC3961 allows implementation of initial startup with optional high-voltage disconnect after starting, and input voltage monitoring with turnoff for either undervoltage or overvoltage conditions. Other features include power-switch current protection, pulse-by-pulse current limiting, shutdown after a programmable delay and continuous input voltIn a non-typical use, the UCC3961 can accommodate an analog feedback signal through an opto-isolator where the UCC3961 then can operate in voltage-mode control mode with primary-side peak current limiting.
The UCC3961 and the UCC2961 are available in the 14-pin SOIC D and PDIP P packages. For applications where only startup and control are desired, a simplified version of this product is offered in an 8-pin package as the UCC2960 and UCC3960.