Gheorghe Brezeanu

Variable Off-Time Control Loop for Current-Mode Floating Buck Converters in LED Driving Applications

A versatile controller architecture, used in current-mode floating buck converters for LED driving, is developed. State-of-the-art controllers rely on a fixed switching period and variable duty cycle, focusing on current averaging circuits. Instead, the proposed controller architecture is based on fixed peak current and adaptable off time as the average current control method. The control loop is comprised of an averaging block, transconductance amplifier, and an innovative time modulator. This modulator is intended to provide constant control loop response regardless of input voltage, current storage inductor, and number of LEDs in order to improve converter applicability for LED drivers. Fabricated in a 5 V standard 0.5 μm CMOS technology, the prototype controller is implemented and tested in a current-mode floating buck converter. The converter exhibits sound continuous conduction mode (CCM) operation for input voltages between 11 and 20 V, and a wide inductor range of 100-1000 μH. In all instances, the measured average LED current variation was lower than 10% of the desired value. A maximum conversion efficiency of 91% is obtained when driving 50 mA through four LEDs (with 14 V input voltage and an inductor of 470 μH). A stable CCM converter operation is also proven by simulation for nine LEDs and 45 V input voltage.

Schottky Oxide Ramp Diodes

The sections in this article are 1 Simulation 2 Device Fabrication 3 Analytical Model 4 Conclusions

Two Packaging Solutions for High Temperature SiC Diode Sensors

A partially electrically isolated package with a gold wire and fully isolated solution with a metallic piston, respectively, are designed and tested for high temperature sensors (400°C) based on SiC Schottky barrier diodes (SBD). Electrical behavior and sensor performance are very close for both packaging solutions. The stress due to contact pressure and higher cost are some disadvantages for pressure contact technology.

Investigation of electro-thermal behaviour of a linear voltage regulator and its protection circuits by simulator coupling

This paper presents an electro-thermal co-simulation method which can be used for thorough verification of linear voltage regulators. The method can capture successfully the electro-thermal interaction between the power stage elements and the protection circuits, accounting also for layout variations and packaging conditions. An electro-thermal destruction mechanism of a high power linear voltage regulator (20W/mm2) is investigated in this way. The simulated results have been shown to replicate the measured behavior of the circuits.

Variable off time current-mode floating buck controller - A different approach

Switch-mode power supplies have become the premier choice for LED backlighting applications. This paper introduces a new current-mode floating buck controller architecture, used for driving constant current through a string of LEDs. Unlike state-of-the-art controllers, this architecture is based on fixed peak current and variable OFF time as the current control method. An innovative time modulator is added to provide a constant feedback loop response regardless of external components. The proposed controller architecture is designed, implemented in a 0.5μm CMOS process and its performances are validated by simulations and measurements.

Time modulation — The exponential way

A solution for obtaining an exponential variation of time versus input voltage of a time-modulating circuit is investigated, implemented and its performances are measured. Most time-modulating circuits produce a delay that is linearly dependent on the input voltage. This paper proposes a new method of controlling the time delay output by making it vary exponentially with the input voltage. This solution is especially useful in aplications where the time-delay is constantly modulated by a prior error amplifier.

Temperature behavior of 4H-SIC MOS capacitor used as a gas sensor

Temperature behavior of 4H-SiC MOS capacitor is investigated. A new layout with several active MOS structures is proposed. Measured C-V characteristics show good thermal stability up to 300 C. The main electrical parameters of the MOS structure have been extracted by measurements on wafer and encapsulated samples.

Substrate leakage current influence on bandgap voltage references in automotive applications

This paper presents a study of the influence of the substrate leakage current on the output voltage of a well-known bandgap architecture with second order compensation. In addition, an analytical approach for the output voltage is provided. The bandgap voltage reference has been successfully implemented in a standard BiCMOS technology on an effective area of 0.07mm2. A low quiescent current of 4μA and a very small variation of the output voltage have been achieved over the whole temperature range by eliminating the effect of the leakage current. Therefore, a variation of 3mV has been measured for the whole operating temperature range (-40°C to 170°C).

Novel Buried Field Rings Edge Termination for 4H-SiC High-Voltage Devices

This paper is concerned with a numerical study of a novel edge te rmination technique for 4H-SiC high voltage devices. For the first time, Buried Field Rings (BFRs) are proposed to be used in SiC devices as an effective termination method and the concept is numerical ly demonstrated for 4H-SiC MESA JFET structures. By using 4 BFRs at the periphe ry of a MESA JFET, a breakdown voltage of 1590V has been achieved, representing more than 90% of the ideal bulk breakdown value (1750V). The doping concentration sensitivity of the rings and the effect of the SiC/SiO2 interface charge on the blocking capability are studied, evidencing the robustness of the novel concept in terms of process conditions and doping variations. For compar ison, some results for GRs and JTE are also presented.

Double epitaxial layer power Schottky diodes with end in the ramp oxide technique

Abstract The paper reports a new power Schottky diode (PSD) structure, with a double epitaxial layer and oxide ramp edge. This structure was designed to enhance the forward current capability and the resilience to reverse current transient pulses of the PSD with only minor decreases in the maximum working reverse voltage capability ( V RWM ). Two different metallization types for the Schottky contact were investigated, namely: Ti:Al for devices intended for operation with T j max = 150°C and Cr:Ni:Ag for diodes with T j max = 125°C, respectively.