Hybrid monolithic integration of high-power DC-DC converters in a high-voltage technology

The supply of electrical energy to home, commercial, and industrial users has become ubiquitous, and it is hard to imagine a world without the facilities provided by electrical energy. Despite the ever increasing efficiency of nearly every electrical application, the worldwide demand for electrical power continues to increase, since the number of users and applications more than compensates for these technological improvements. In order to maintain the affordability and feasibility of the total production, it is essential for the distribution of the produced electrical energy to be as efficient as possible. In other words the loss in the power distribution is to be minimized. By transporting electrical energy at the maximum safe voltage, the current in the conductors, and the associated conduction loss can remain as low as possible. In order to optimize the total efficiency, the high transportation voltage needs to be converted to the appropriate lower voltage as close as possible to the end user. Obviously, this conversion also needs to be as efficient, affordable, and compact as possible. Because of the ever increasing integration of electronic systems, where more and more functionality is combined in monolithically integrated circuits, the cost, the power consumption, and the size of these electronic systems can be greatly reduced. This thorough integration is not limited to the electronic systems that are the end users of the electrical energy, but can also be applied to the power conversion itself. In most modern applications, the voltage conversion is implemented as a switching DC-DC converter, in which electrical energy is temporarily stored in reactive elements, i.e. inductors or capacitors. High switching speeds are used to allow for a compact and efficient implementation. For low power levels, typically below 1 Watt, it is possible to monolithically implement the voltage conversion on an integrated circuit. In some cases, this is even done on the same integrated circuit that is the end user of the electrical energy to minimize the system dimensions. For higher power levels, it is no longer feasible to achieve the desired efficiency with monolithically integrated components, and some external components prove indispensable. Usually, the reactive components are the main limiting factor, and are the first components to be moved away from the integrated circuit for increasing power levels. The semiconductor components, including the power transistors, remain part of the integrated circuit. Using this hybrid approach, it is possible in modern converterapplications to process around 60 Watt, albeit limited to voltages of a few Volt. For hybrid integrated converters with an output voltage of tens of Volt, the power is limited to approximately 10 Watt. For even higher power levels, the integrated power transistors also become a limiting factor, and are replaced with discrete power devices. In these discrete converters, greatly increased power levels become possible, although the system size rapidly increases. In this work, the limits of the hybrid approach are explored when using so-called smart-power technologies. Smart-power technologies are standard lowcost submicron CMOS technologies that are complemented with a number of integrated high-voltage devices. By using an appropriate combination of smart-power technologies and circuit topologies, it is possible to improve on the current state-of-the-art converters, by optimizing the size, the cost, and the efficiency. To determine the limits of smart-power DC-DC converters, we first discuss the major contributing factors for an efficient energy distribution, and take a look at the role of voltage conversion in the energy distribution. Considering the limitations of the technologies and the potential application areas, we define two test-cases in the telecommunications sector for which we want to optimize the hybrid monolithic integration in a smart-power technology. Subsequently, we explore the specifications of an ideal converter, and the relevant properties of the affordable smart-power technologies for the implementation of DC-DC converters. Taking into account the limitations of these technologies, we define a cost function that allows to systematically evaluate the different potential converter topologies, without having to perform a full design cycle for each topology. From this cost function, we notice that the de facto default topology selection in discrete converters, which is typically based on output power, is not optimal for converters with integrated power transistors. Based on the cost function and the boundary conditions of our test-cases, we determine the optimal topology for a smart-power implementation of these applications. Then, we take another step towards the real world and evaluate the influence of parasitic elements in a smart-power implementation of switching converters. It is noticed that the voltage overshoot caused by the transformer secondary side leakage inductance is a major roadblock for an efficient implementation. Since the usual approach to this voltage overshoot in discrete converters is not applicable in smart-power converters due to technological limitations, an alternative approach is shown and implemented. The energy from the voltage overshoot is absorbed and transferred to the output of the converter. This allows for a significant reduction in the voltage overshoot, while maintaining a high efficiency, leading to an efficient, compact, and low-cost implementation. The effectiveness of this approach was tested and demonstrated in both a version using a commercially available integrated circuit, and our own implementation in a smart-power integrated circuit. Finally, we also take a look at the optimization of switching converters over the load range by exploiting the capabilities of highly integrated converters. Although the maximum output power remains one of the defining characteristics of converters, it has been shown that most converters spend a majority of their lifetime delivering significantly lower output power. Therefore, it is also desirable to optimize the efficiency of the converter at reduced output current and output power. By splitting the power transistors in multiple independent segments, which are turned on or off in function of the current, the efficiency at low currents can be significantly improved, without introducing undesirable frequency components in the output voltage, and without harming the efficiency at higher currents. These properties allow a near universal application of the optimization technique in hybrid monolithic DC-DC converter applications, without significant impact on the complexity and the cost of the system. This approach for the optimization of switching converters over the load range was demonstrated using a boost converter with discrete power transistors. The demonstration of our smart-power implementation was limited to simulations due to an issue with a digital control block. On a finishing note, we formulate the general conclusions and provide an outlook on potential future work based on this research

Active asynchronous secondary side voltage clamping

An asynchronous active voltage clamp for the secondary side of switching DC-DC converters is proposed. The control of the proposed clamping circuit is independent from the main converter, thus allowing use of a physically small inductor and offering increased control over the clamping operation. Measurements on a 1 MHz implementation of the asynchronous active voltage clamp on the secondary side of a prototype 220 kHz phase shifted full bridge DC-DC converter confirm the effectiveness of the voltage clamping and the improved converter efficiency

Driving electronics for OLED lighting

This paper proposes the concept of integrating an OLED (foil) and its driving electronics into one module. A complete light system consisting of these modules is the ultimate goal of this work. The main focus in this article is on the design of the driver chip and the circuit implementation. The measurement results confirm that it is possible to control the light output of the different modules

Numerical simulation of a multi-inlet microfluidic device for biosensing purposes in osteoporosis management

Objectives In this paper, the effect of the position of the inlet and outlet microchannels on the flow profile and the geometry of the recognition chamber for sample pre-treatment in an electrochemical biosensor to be used in osteoporosis management were investigated. Methods All numerical computation presented in this work were performed using COMSOL Multiphysics and Fluent. Simulation was performed for a three-dimensional, incompressible Navier-Stokes flow and so explicit biphasic volume of fluid (VOF) equations were used. Results In the designed microfluidic system, a pressure-driven laminar flow with no-slip boundary condition was responsible for fluid actuation through microchannels in a reproducible approach. Based on the simulation results, the number of outlets was increased and the angel through which the inlets and outlets were attached to the microchamber was changed so that the dead volume would be eliminated and the fluid flow trajectory, the velocity field and pressure were evenly distributed across the chamber. The Re number in the inlets was equal to 4.41, suggesting a laminar flow at this site. Conclusion The simulation results along with the fact that the design change was tested using laser ablated tape and a color dye at different steps provided the researchers with the opportunity to study the changes in a fast and accurate but cheap method. The absence of backflow helps with the cross-talk concern in the channels and the lack of bubbles and complete coverage of the chamber helps with a better surface modification and thus better sensing performance

Design, construction and testing of a COC 3D flow-over flow-through bioreactor for hepatic cell culture

In this poster, we present the joint development efforts for a 3D microfluidic bioreactor for hepatic cell cultures. Cyclic Olefin Copolymer (COC) was selected for constructing the bioreactor, since the material has good chemical resistance, low adsorption and good optical properties, including low auto-fluorescence. A downside of COC is that it is much more difficult to structure than more traditional microfluidic materials, such as PDMS, PMMA, … Two parallel approaches were developed for structuring the COC. In a first approach, mechanical micro-milling of the channels allows for extremely fast manufacturing of new design variations, at the expense of difficulties in scalability to mass-production and a channel surface that requires post-processing to achieve sufficient optical quality. In a second approach, hot embossing using epoxy molds allows for direct structuring of optical grade channels and is scalable to mass production, at the expense of longer cycle time in the development of new channel designs. To facilitate the handling of the bioreactor, a holder was designed to provide the fluidic connections to a pump,ensuring medium exchange and sampling to down-stream sensors connected to the outlets. The design of the bioreactor was intended to maintain and expose pre-formed hepatic co-culture spheroids to toxicants for more than a week. Once seeded, spheroids rest on a polycarbonate membrane with 12 µm pore size, allowing the medium to flow-through, while flow-over is maintained to avoid an excess pressure on the cells. In a single bioreactor, 9 wells are connected to a common inlet to provide the cells with fresh culture medium or test compounds. On a first cell culture trial, it was possible to visually detect the spheroids in the wells after seeding, however, after 1 week of culture there was no possibility to accurately detect the presence and viability of the cells. In the framework of HeMiBio, significant progress has been made towards producing a 3D COC-based bioreactor for hepatic cell culture, and most technological hurdles in producing prototype reactors have been overcome. Further testing is needed to see which improvements to the reactor or the flow conditions should be made to ensure cell viability

Monolithic integration of an active asynchronous voltage clamp with a 12V/3A full bridge synchronous rectifier

In transformer isolated converters, a large voltage overshoot is present on the secondary side switching nodes at every switch transition. As is well known in the design of monolithically integrated high voltage circuits, the peak voltage stress in a circuit is the paramount parameter for an efficient implementation of smart-power circuits. A voltage clamping circuit that minimizes the voltage stress in the circuit is crucial for an efficient monolithic implementation of a synchronous rectifier in a smart-power technology. This paper presents a smart-power implementation of an asynchronous active clamping circuit on the same IC as a 12V/3A synchronous rectifier for a full bridge phase shifted dc-dc converter. The asynchronous clamping circuit minimizes the number and size of required external components to provide the voltage clamping, and optimizes the efficiency of the synchronous rectifier by accurately controlling the clamping operation

Design and characterization of a secondary side smart-power integrated active asynchronous voltage clamp

As is well known in the design of transformer isolated converters, the transformer leakage inductance causes a large voltage overshoot on the secondary side switching nodes at every switch transition, unless measures are taken to limit the peak voltage stress. Since the peak voltage stress in smart-power integrated converters, where the power devices are integrated on the same die as the controlling logic and supporting circuits, is the major determining factor for the required silicon area for the implementation, this is a major roadblock for the affordable integration of this type of converter. Therefore, any cost-effective smart-power synchronous rectifier requires a voltage clamping circuit that minimizes the voltage stress, while still maintaining the potential advantages of smart-power converters, i.e. minimizing the number and size of the discrete components in the converter. We present an integrated asynchronous active clamping circuit, that can clamp the overshoot voltage to arbitrary voltages while optimizing the efficiency by only being active when required. Because of the asynchronous operation, the size of the required external components is minimized. Measurements on the smart-power IC implementation of the asynchronous active clamp circuit combined with a secondary side synchronous rectifier for a 1 MHz full bridge converter confirm the reduction in voltage stress and the optimization of the efficiency

Design of an integrated OLED driver for a modular large-area lighting system

The concept of a flexible, large-area, OLED-based lighting system with a modular structure and built-in intelligent light management is introduced. The paper describes the design of a high-voltage integrated circuit for driving and controlling an individual OLED tile in this modular lighting system. The chip comprises a switching DC-DC buck converter for generating the OLED current and a sensitive analog feedback loop for adjusting the duty cycle of the converter’s PWM control signal. The chip was designed in the 80V 0.35µm I3T80 technology of ON Semiconductor