AC/DC Power Supply - Dual Digital Controller

Block diagram (SBD) Server AC/DC Power Supply and Telecom Rectifier using TI’s Digital Controllers, high performance drivers and transceivers.


The challenges AC/DC power supply developers face today are achieving high power factor, low THD, and high efficiency across line and load conditions, high power density or reduced size, high reliability, and low system cost. Advanced power topologies such as interleaved PFC, bridgeless PFC, phase-shifted full-bridge DC/DC, LLC resonant DC/DC, and ZVS PWM DC/DC are commonly employed in today's designs addressing these needs. In addition, OEMs are demanding additional features such as more sophisticated fault diagnosis, power measurement, and more extensive status reporting over I2C or CAN interface.

Digital controllers offer the obvious advantages of combing PWM control and additional features, reducing part count and BOM. They can implement different compensation schemes under different conditions, making it possible to achieve high PF, low THD, and high efficiency across line and load ranges. This can be as simple as using different parameters and as elaborative as shedding phases, throttling back on PWM frequency or switching to a different compensation such as feed forward on sudden line or load change. Techniques such as over sampling or biasing of sensed current can be implemented for example to improve PF and THD at high line and light load. Another advantage of digital controllers is the possibility of different versions of firmware for different product offerings based on the same h/w reducing the time and investment associated with making h/w changes.

Most AC/DC power supplies use dual PWM controllers, a PFC controller and a DC/DC controller. This is also true for applications using TI digital controllers. However, TI's digital controllers can combine both PFC and DC/DC control without compromising either PFC or DC/DC performance. Challenge with using a single controller is output voltage sensing and load sharing control across isolation boundary. Its main advantage is integration and not having to deal with two separate controllers.

Digital controllers rely on fast on-chip ADC to sample and convert the currents and voltages, fast CPU to execute the compensation and update the control or PWM duty, and on flexible PWM module to generate the PWM patterns for different power topologies. They also rely on extra CPU bandwidth and additional peripherals for system supervisory and communication tasks. On-chip analog comparators closely coupled into the PWM generation are also commonly seen peripherals to help save CPU bandwidth and increase loop bandwidth. High PWM resolution is required for high PWM switching frequency which is critically important in today's designs.

Digital controllers rely on executing software code to perform control and system supervisory functions. So, robust code development and debugging tools are critical.

The High performance FET Drivers-UCD7XXX family features high speed, high current, and FAST over-current protection. It is designed to directly interface with digital controllers. TI's UCC27xxx drivers are also used with digital controllers.

TI's Integrated Hot Swap Power Controllers are optimized for nominal -48V systems. The devices provide load current slew rate control and peak magnitude limiting. Most of the Hot Swap Controllers have digital interface for precise programming and monitoring and also have Power good and fault outputs.

Other high-performance analog parts are also available to provide critical system functions and features such as sensor feedback, isolation, communication transceivers.

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