Gyu-Ha Cho

A Single-Inductor Switching DC–DC Converter With Five Outputs and Ordered Power-Distributive Control

An integrated 5-output single-inductor multiple-output DC-DC converter with ordered power-distributive control in a 0.5mum BiCMOS process is presented. The converter has four main positive boost outputs programmable from +5 to +12V and one dependent negative output from -12 to -5V. A maximum efficiency of 80.8% is achieved at a total output power of 450mW, with a switching frequency of 700kHz.

Modeling and analysis of a static VAR compensator using multilevel voltage source inverter

A multilevel PWM (pulse-width-modulated) voltage source inverter, especially a five-level one, is introduced to obtain a static VAr compensator (SVC) as a large-scale power source. The three phase SVC is modeled using circuit DQ transformation and completely analyzed including DC and AC characteristics. Through experimental results for a 5 kVA SVC, the validity of the analyses and the feasibility of the VAr compensation system are shown for high-power applications.<<ETX>>

A Single-Inductor Step-Up DC-DC Switching Converter with Bipolar Outputs for Active Matrix OLED Mobile Display Panels

A single-chip dual-output step-up DC-DC converter is implemented for active-matrix OLED mobile display panels. The bipolar outputs are regulated independently and integrated with a boost and a charge-pump topology sharing a single inductor. The chip is 4.1mm2 fabricated in a 0.5 mum power BiCMOS process and operates at 1MHz with a maximum efficiency of 82.3% at an output power of 330mW.

A Single-Inductor Step-Up DC-DC Switching Converter With Bipolar Outputs for Active Matrix OLED Mobile Display Panels

A single-inductor step-up DC-DC switching converter with bipolar outputs is implemented for active-matrix OLED mobile display panels. The positive output voltage is regulated by a boost operation with a modified comparator control (MCC), and the negative output voltage is regulated by a charge-pump operation with a proportional-integral (PI) control. The proposed adaptive current-sensing technique successfully supports the implementation of the proposed converter topology and enables the converter to work in both discontinuous-conduction mode (DCM) and continuous-conduction mode (CCM). In addition, with the MCC method, the converter can guarantee a positive output voltage that has both a fast transient response of the comparator control and a small output voltage ripple of the PWM control. A 4.1 mm2 converter IC fabricated in a 0.5 mum power BiCMOS process operates at a switching frequency of 1 MHz with a maximum efficiency of 82.3% at an output power of 330 mW.

Load-Independent Control of Switching DC-DC Converters with Freewheeling Current Feedback

In this paper, a load-independent converter with freewheeling current feedback, whose output is controlled by a comparator, is presented. This control method is very useful for single-inductor multiple-output (SIMO) converters. A single-inductor bipolar-output (SIBO) converter with the proposed control scheme is implemented in a 0.5 mum power BiCMOS process and uses 3.2 mm2 of die area. The current sensing gain can be increased and and the circuit is less sensitive to switching noise than CPM converters are because the slope compensation used in CPM converters reduces the current sensing gain to comply with low supply voltage.

Modeling, analysis and control of static VAr compensator using three-level inverter

A novel static VAr compensator (SVC) system using a three-level inverter is proposed for high-voltage and high-power applications. A general and simple model for the overall system is obtained using the circuit DQ-transform, and DC and AC analyses are performed to characterize the open-loop system. Using the proposed model, a novel control method which controls both the phase angle and the modulation index of the switching pattern simultaneously is suggested to provide fast response of the SVC system without using the independent voltage source. Predicted results are verified by computer simulation.<<ETX>>

A PLL-based high-stability single-inductor 6-channel output DC-DC buck converter

Cost and size are very important issues for power-management ICs (PMICs), in particular for portable systems where typically multiple voltage levels are required to achieve multi functionality. To meet these requirements, a single-inductor multiple-output (SIMO) switching converter is a very strong candidate. SIMO converters have been the subject of many recent studies and reports [1–3]. The presented converters uses the current-mode controller and PWM with a constant switching frequency. However, designing the feedback control loop of the PWM converters is not an easy task since their stability inherently depends on the load conditions.

Load-Independent Control of Switching DC-DC Converters With Freewheeling Current Feedback

A new control scheme of freewheeling current control is proposed for switching DC-DC converters. The output voltage is regulated by a comparator operation, and in the main current loop, the freewheeling current is feedback-controlled to a reference level in average. The converter control loop is no longer dependent on the values of the inductor, output capacitor, or the load equivalent resistance. The design of a loop compensator is therefore greatly simplified and the loop response can be very fast approaching that of a hysteresis converter. As an example, a single-inductor bipolar-output DC-DC converter with the proposed freewheeling current control is implemented in a 0.5 mum BiCMOS process. The converter has one positive output of 4 V and one negative output of -4.8 V. A maximum efficiency of 81% is achieved at a total output power of 250 mW with a switching frequency of 800 kHz.

Multiple-output step-up/down switching DC-DC converter with vestigial current control

A single-inductor dual-output boost converter reported in [1] works either in discontinuous conduction mode or in pseudo-continuous conduction mode and requires separate controllers. As each controller regulates the output in time-multiplexed manner, it is difficult to extend the number of outputs and power capacity. The converter reported in [2] solves these limitations by adopting comparator-controlled method. Each comparator-controlled output receives its required energy and one final PWM controller adjusts the total inductor current so that the remaining current is adequate for the last output. However, as the PWM controller regulates one of the converter outputs, the response of controller becomes slow and voltage ripple of the other outputs increases when the load current of PWM-controlled output is reduced to zero (or near zero). As a possible solution, minimum bleeding current can be set for the last output, however, this approach degrades the efficiency at light-load condition. Also, the operation region of the previously reported multiple-output converters is restricted to step-up mode only.

A high-stability emulated absolute current hysteretic control single-inductor 5-output switching DC-DC converter with energy sharing and balancing

Several types of DC-DC converters for active-matrix organic LED (AMOLED) displays have been introduced to date [1-4]. Single-inductor multiple-output (SIMO) converters with current-mode control have many advantages including reduced PCB space and less cost for mass-production due to the use of only one off-chip inductor to provide many outputs [1,2]. However, a load-dependent stability issue has to be addressed which is due to the output capacitance and an internal integrator with an error amplifier. Recently, in efforts to overcome the stability issue of current-mode control, load-independent control converters have been developed. Although this concept works well, the inductor-current sensing and artificial ramp generation for stability still make the controller complicated [3,4]. In addition, the freewheeling current control converter requires an extra power switch for freewheeling current flow, thereby lowering power efficiency [3]. The vestigial current control converter, meanwhile, has weak points of requiring auxiliary output and an additional inductor, and thus consumes some additional power in the steady state [4]. Besides the controller issue, the previous converters when operating with a large step-up ratio, usually have heavy voltage stress applied to the inductor, resulting in a low efficiency [1,4]. To overcome these problems, the proposed SIMO converter employs emulated absolute current hysteretic control, which uses full current information and is characterized by intrinsic high stability. The energy sharing capacitor is also used for high output voltage to reduce the voltage swing of the switching node and the associated loss. In addition, to balance the total energy across the inductor, the energy balancing capacitor is adopted.