Ramanujam Ramabhadran

A low power consumption driver with low acoustics for piezoelectric synthetic jets

The low profile piezoelectric synthetic jet is a promising approach for forced air convection cooling of electronics for high density and portable applications. The synthetic jet considered in this paper, known as a DCJ ([2]), consists of a pair of piezoelectric discs mounted on a frame and driven with a voltage, which causes the discs to mimic the action of a pair of bellows. This DCJ requires a sinusoidal waveform of 125-175 Hz at an amplitude up to bQV, and must operate from a 5V DC source. The mostly capacitive load of the DCJ presents a challenge for typical amplifiers. Furthermore, many applications require quiet operation; hence the jet driving waveform must have very low distortion to prevent audible acoustic noise. This paper describes a bidirectional power driver topology for driving capacitive loads based on a dual flyback topology, along with a low-cost, pure sine reference generator with predistortion to allow a clean output waveform without feedback. The driver achieves low power consumption (rì 250mW) with low harmonic content. The use of predistortion and a delta-sigma DAC compensates for the inherent flyback converter nonlinearity and the low resolution DAC typical of low-cost microcontrollers. The paper describes and presents experimental results for a design that accomplishes these objectives in a 30 mm × 30 mm × 4 mm volume.

Investigation of CCM boost PFC converter efficiency improvement with 600V wide band-gap power semiconductor devices

Wide band-gap materials such as Gallium Nitride (GaN) and Silicon Carbide (SiC) offer improved performance for power electronic devices compared to traditional Silicon (Si) power semiconductor devices. This paper investigates a 600V GaN & Silicon CoolMOS transistor application in 400W single phase continuous conduction mode (CCM) Boost PFC converter circuits with GaN, SiC and ultrafast silicon diodes and compares power semiconductor device efficiency benefits. The 600V GaN & Silicon CoolMOS transistor power efficiency improvement study and loss analysis for CCM Boost PFC converter circuits are introduced in detail. Based on the experimental study, the 600V GaN transistor enables higher energy efficiency compared with 600V Si CoolMOS for CCM Boost PFC converter at 680 kHz switching frequency: around 1% higher at low line and about 0.5% higher at high line due to low switching loss. 600V SiC diode typically outperforms ultrafast Si diode & GaN diode for CCM Boost PFC converter due to low device charge, and forward voltage. 600V GaN diode suffers lowest efficiency at light load due to large device capacitive charge. The ultrafast Silicon diode has the highest efficiency at light load due to low device charge, but suffers from low efficiency at heavy load due to largest forward voltage and reverse recovery loss. According to the investigations, the combination of a 600V GaN transistor for the boost switch and a SiC rectifier for the freewheeling diode achieves the best efficiency for CCM Boost PFC converter with the lowest power loss.

Universal AC input high density power adapter design with a Clamped Series Resonant Converter

In this paper, we present the design and fabrication of a high density laptop adapter with a Clamped Series Resonant Converter (CSRC), as a possible alternative to traditional Flyback converters for power adapters in portable electronics. The target is to design for universal AC input up to a power of 100 W with power density of 6-7 W/in3. The converter is frequency controlled, and all switches exhibit Zero-Current Switching (ZCS). In this paper, we show that by utilizing the magnetizing inductance, the converter can be tuned for Zero Voltage Switching (ZVS), and by adding a switched capacitor circuit to extend the input voltage range, we can realize a very compact design that is suitable for power adapters with or without power factor correction. Low transformer stresses compared to Flyback type designs enable high densities, even with a resonant magnetic. Prototype test results with a 45 W laptop adapter are presented. Our initial testing with diode rectification indicated very good efficiency. Versions with synchronous rectification promise higher efficiencies by at least 1%, which will be ideal for energy saving low power devices.

Comparative study of half-bridge LCC and LLC resonant DC-DC converters for ultra-wide output power range applications

The Half-Bridge (HB) LCC resonant DC-DC converter and HB LLC resonant DC-DC converter circuit are comparatively studied for high efficiency ultra-wide output power range application in this paper. The output voltage ranges from minimum output voltage to twice that value. And the output current ranges from 10% load to 100% load. So the output power spans over a wide range, from minimum to 20 times that. The detailed resonant tank characteristics analysis for HB LCC and LLC resonant converter is provided. Through the 150W hard prototype experiments validation, it is shown that HB LLC resonant DC-DC converter can achieve better performance with flat efficiency, narrow switching frequency range compared with HB LCC resonant DC-DC converter for wide output current application at both 75V & 150V output voltage from 10% output current to 100 % output current conditions. HB LLC resonant DC-DC converter is more preferred power conversion circuit topology to achieve high performance with flat efficiency, narrow switching frequency range in ultra-wide output power range applications.

Low THD multipliers for BCM buck and cascaded buck-boost PFC converters

Boundary conduction mode control is a convenient and low cost method for realizing power factor correction in boost and flyback converters. A signal proportional to the input sinusoid is used as a reference for shaping an inductor current. For a boost converter, this renders the input current to be sinusoidal, but it causes distortion in Flyback and buck derived converters. Mathematically, it can be shown that a different multiplier is needed for buck derived and Flyback converters to achieve a sinusoidal input current. In this paper, we develop peak current reference multipliers for Boundary Conduction Mode (BCM) control of buck derived converters. These multipliers are to be implemented in typical low cost BCM controllers. We derive a new multiplier for a buck PFC, and extend this to a cascaded buck boost (also known as a four switch buck boost) PFC as a composite multiplier. For the cascaded buck boost, we also implement a control scheme to handle the transition between buck and boost modes. We provide experimental results in both topologies.

Analysis, design and implementation of CLL resonant DC-DC converter for wide output power range applications

This paper proposes a half bridge CLL resonant DC-DC converter for wide output power range applications. This topology can achieve zero-voltage switching at entire load and zero-current switching for output rectifiers. The characteristics of the CLL resonant DC-DC converter are analyzed firstly. Then the design considerations for CLL resonant DC-DC converters based on wide output power range are introduced. An 150W CLL resonant converter prototype is built to verify the circuit performance with good performances on flat efficiency, narrow switching frequency range for wide output power range application at both 75V & 150V output voltage from 10% output current to 100 % output current.