Prof. Deepak Divan Satish Rajagopalan

1. Prof. Deepak Divan Satish Rajagopalan Quasi Linear DC/DC ConvertersA New Approach for Realizing Efficient DC Power Supplies with Linear Operating Characteristics Sponsored by IPIC, Georgia Institute of Technology Problem: Need for High Performance DC/DC Converters Quasi Linear DC/DC Converters – One Possible Implementation • Demanding applications, such as medical imaging, fast processors, and pulsed loads are requiring new levels of performance from DC/DC converters • Extremely low ripple voltages • Sub-cycle response and settling times (new Intel processors consume 100 A with slew rates > 150A/µs and ΔV = 50 mV) • High efficiency and small size • Conventional design approaches are not able to meet these needs easily New Approach • A new hybrid technique to realize linear power supply performance with switched mode DC/DC converter efficiency and size is proposed • The proposed quasi linear building block can implement buck, boost and buck-boost functionality, as well as isolated converter functions • Two MOSFETs Q2 and Q3 and resistor Rs are added to a normal Buck Converter • Two operations are carried out simultaneously • Voltage source follower operation of Q2 in the ohmic region for regulated ripple free output voltage • Current injection through Q3 and Rs to provide fast response during step change in load Conventional Realization of High Performance Converters 4-phase, 120A, 6.5-12VIN, 0.8-3.3VOUT Multiphase Buck Converter Photo Courtesy: International Rectifier Quali-Buck Simulation Results in SABER Top: Load current Middle: Buck converter output Bottom: Voltage at load Top: Current through transistor Q3 Middle: Hysteritic comparator output to control Q3 Bottom: Voltage at Buck output Multiphase PC VRMs Photo Courtesy: Artesyn Technologies Quali-Buck Experimental Results Quasi Linear DC/DC Converters – Principle of Operation With current injection and voltage follower Without current injection and voltage follower Buck regulator (12V → 5V) at 25 KHz switching frequency (2x47uF MLC Bulk Capacitors); Load switching at 100 Hz Top trace (Pink): Buck output voltage, Middle trace (Green): Output load voltage, 50mV/div -> 2.5V/div; Lower trace (Blue): Load current 5A/div Quasi Linear Converter Design Trade-Offs And Conclusions • The design trade-offs for quasi linear DC/DC converters appear to be significantly different from conventional DC/DC converters • The switching frequency and transient response to load/source deviations are completely decoupled and can be set independently of each other • As high switching frequency is no longer needed, we can trade-off switching losses for losses in Q2, giving minimal impact on η • Eliminates need for large electrolytic caps, reducing size • Can be implemented over wide range of power and voltage levels • The quasi linear converter comprises of conventional switching converter and a “linearizer” • Linearizer block can be added on to any switching converter and increases voltage regulation and transient response time • Partitioning of conventional switching regulator and “linearizer” allows integration with local loads such as µPs • In DC/DC converters such as the Boost converter, the right half plane zero is eliminated thereby simplifying control P30 Intelligent Power Infrastructure Consortium –IPIC