Low-side Power Research Articles

A Novel ZVS/ZCS Push-Pull LC Resonant DC-DC Converter for Energy Sources

In this paper, a novel soft switching push-pull LC resonant DC-DC converter for energy sources is presented. In a high step-up converter, the input of primary side possesses low voltage and high current, so the losses caused by the current account for most of the total power loss. At the same time, the high-voltage stress of the high-voltage output components on the secondary side is also a major problem. Therefore, a high-gain isolated push-pull converter with a secondary-side resonant circuit is proposed, so that the primary-side switches have zero voltage switching (ZVS) and the secondary-side diodes have zero current switching (ZCS). The push-pull structure can reduce the number of active switches, so that the total power loss on the primary side can be reduced. The converter has a resonant tank circuit arranged between the secondary side of isolation transformer and the high-voltage output rectification module. The high-voltage output rectifier module adopts a full-bridge architecture suitable for high-voltage coupling connection. The low-side power switching module adopts a push-pull architecture suitable for low-voltage and high-current applications. The resonant tank circuit uses an inductor–capacitor (LC) structure to improve the resonant tank circuit, which achieves soft switching during power transfer, increasing the efficiency of the converter and improving the electromagnetic compatibility. The main advantage of this technology is that the secondary-side leakage inductance of transformer and the resonant capacitance are connected in series to achieve ZVS for switches and ZCS for diodes. Finally, a prototype of a high-gain push-pull resonant converter was established. The converter was operated at a fixed switching frequency of 135 kHz and a duty cycle of approximately 0.5. The efficiency of the converter can reach 97.1% under experimental tests at an output voltage of 400 V and a rated output power of 500 W.

GaN on Engineered Bulk Si (GaN-on-EBUS) Substrate for Monolithic Integration of High-/Low-Side Switches in Bridge Circuits

A cost-effective engineered bulk silicon (EBUS) substrate technology is presented, featuring p-n junction implemented on bulk Si substrates using mainstream ion implantation and thermal annealing processes. Standard p-GaN/AlGaN/GaN heterostructures are successfully grown on the EBUS substrate and used to fabricate 200-V enhancement-mode p-GaN gate HEMTs. By creating deep trenches in the EBUS substrate to isolate the local P+ silicon regions underneath the high-side (HS) and low-side (LS) power switches, adverse effects (e.g., back-gating and dynamic ON-resistance degradation) in the use of conventional bulk Si substrate are all eliminated. The mechanism of crosstalk suppression in the GaN-on-EBUS platform is revealed in comparison with conventional GaN-on-Si platform and verified by a series of designed tests.

GaN-on-Si: Monolithically Integrated All-GaN Drivers for High-Voltage DC-DC Power Conversion

This paper presents a novel integrated half-bridge driver architecture using GaN-on-Si process for high-speed and high-voltage DC-DC converters. The entire circuit includes only enhancement mode (E-mode) and depletion-mode (D-mode) GaN transistors. The high-side driver circuit adopts the E-stacked E/D-mode (EED) architecture, which can directly drive the gate of the high-side transistor with a low-voltage signal without using an additional level shifter, which simplifies the design and reduces propagation delay. In addition, the low-side power transistor is driven by stacking two D/E-mode devices. This architecture separates the high-side pulse from the low-side drive signal to prevent false triggering of the low-side driver. The designed fully integrated GaN driver can output a high-voltage pulse wave with an operating frequency greater than 1 MHz when the input voltage is greater than 200 V. The rise and fall times of the high-voltage pulse wave operating at a peak voltage of 200 V are 54.4 ns and 57.6 ns, respectively. The experimental results show that the circuit can effectively drive the half-bridge circuit and be applied to a buck converter. The designed buck converter can deliver up to 20.5 W of output power, and the maximum efficiency achieves 90.7%.

A Constant On-Time Control With Internal Active Ripple Compensation Strategy for Buck Converter With Ceramic Capacitors

Constant on-time control has been widely used due to its advantages of fast transient response and light load efficiency. However, the control scheme is intrinsically unstable if the output capacitor's equivalent series resistance (ESR) is not large enough, which needs ripple injection techniques to enhance loop stability. The traditional passive ripple compensation technique uses only passive component networks to realize this function, which exhibits some inherent shortcomings, including difficulties in high-speed current sensing amplifier design and large chip area consumption. This paper proposes an internal active ripple compensation strategy that senses the low-side power mosfet current and extracts relevant ac information for feedback-ripple enhancement. Output-voltage dc offset does not occur and subharmonic instability is significantly improved even with ceramic capacitors. The circuit architecture has been realized in a synchronous buck regulator with a 0.5 μm 40 V bipolar-CMOS-DMOS (BCD) process. The programmable switching frequency is up to 1 MHz and the maximum load current is 4 A. Simulation and experimental results are given to prove the proposed high performance.

Synchronous High Step-Down Ratio Non-Isolated LED Constant Current Driver Based on Improved Watkins-Johnson Topology

In the field of non-isolated light-emitting diode (LED) driver, the omnipresent buck-based LED constant current driver shows poor efficiency in occasions of high step-down ratio due to the marginal operating duty cycle. In order to overcome such drawback and to provide an alternative topological scheme for an LED driver, a Watkins-Johnson topology-based solution is proposed in this paper, by improving the original circuit structure into a dual low-side power switch version and introducing a feedback network for regulating the output current to a constant level. Theoretical analysis, including accurate model construction, steady-state analysis, dynamic analysis, and design consideration, is conducted. Also, an experimental prototype is realized to drive all kinds of LED arrays for acquiring electrical parameters and evaluating performance. The innovative points include invoking the low-side-ize approach to realize the power circuit transformation, and furthermore, theWatkins-Johnson topology is first applied to the constant current power supply. The proposed LED driver holds salient features of low-terminal current ripple, ease of driving, high-voltage conversion ratio tolerance, and inherent energy recovery functionality. The application scope covers low-voltage dc input or automotive lighting use.

A High-Frequency Three-Level Buck Converter With Real-Time Calibration and Wide Output Range for Fast-DVS

This paper presents a 50-MHz 5-V-input 3-W-output three-level buck converter. A real-time flying capacitor ( $C_{F}$ ) calibration is proposed to ensure a constant voltage of $V_{g}$ /2 across $C_{F}$ , which is highly dependent on various practical conditions, such as parasitic capacitance, time mismatches, or any loading circuits from $C_{F}$ . The calibration is essential to ensure the reliability and minimize the inductor current and output voltage ripple, thus maintaining the advantages of the three-level operation and further extending the system bandwidth without encountering sub-harmonic oscillation. The converter is fabricated in a UMC 65-nm process using standard 2.5-V I/O devices, and is able to handle a 5-V input voltage and provide a 0.6–4.2-V-wide output range. In the measurement, the voltage across $C_{F}$ is always calibrated to $V_{g}$ /2 under various conditions to release the voltage stress on the high- and low-side power transistors and $C_{F}$ , and to ensure reliability with up to 69% output voltage ripple reduction. A 90% peak efficiency and a 23–29-ns/V reference-tracking response are also observed.

Integrated isolation functions for driving power semiconductor devices

This paper presents several innovative solutions in the view of transferring gate signal orders for power semiconductor devices. While considering both monolithic and heterogeneous integration approaches, three different solutions are presented both theoretically and experimentally. The first integration scheme for the required signal insulation unit is based on integrated optical detectors; optical detectors are designed, fabricated and characterized when integrated within vertical power semiconductor devices and within a CMOS gate driver. The DC and AC performances of the first prototypes are compatible with the requirements and specifications for power converters. As a complementary and competitive integration approach, integrated coreless transformers within CMOS gate drivers are designed and characterized. A particular experimental investigation of high frequency coupling is described. A CMOS gate driver containing both a coreless transformer and other necessary functions is applied to a buck converter. Such an integrated circuit is then used to drive a high side and low side power transistor.

A Gate Driver with Integrated Dead-Time Controller

Deadtimes are required to avoid simultaneous conduction of high-side and low-side power transistors in half-bridge power converters. During these secure times, free-wheeling current flow generates extra power losses. Very short deadtimes are desired but they cannot be safely set in conventional isolated power converters because of a digital input propagation delay mismatch. A specific deadtime management is introduced in this paper to ensure proper operation of a high-voltage synchronous power converter. A controller integrated in each isolated gate driver secures synchronous switching by detecting the opposite switch turn-off before turn-on. With such a selfswitching technique, very short but safe nonoverlap times can be set. A gate driver has been implemented in a 0.35 μm 20-V CMOS process. The monolithically integrated controller consumes only 140 μA and 0.22 mm2 of silicon area. The proposed local deadtime management has been validated in two synchronous buck converters without external free-wheeling diodes: a 500-W 250-V to 55-V converter based on SiC JFETs and a 30-W 45-V to 10-V converter based on eGaN FETs. In either case, the proposed controller allows a higher efficiency from 10% of the rated load with resulting deadtimes as short as 15 ns.

Zero‐current switching method for dc–dc buck converter in portable application

A novel zero-current switching (ZCS) method for dc–dc buck converter is proposed. Instead of a conventional high precision and high speed comparator, a comparator with adaptive offset is designed here. By detecting the conduction of parasitic body diode after low-side power transistor turned off, the offset is automatically adjusted to achieve ZCS. Thus the delay and offset of comparator are no longer an obstacle in circuit design and the measurement results show that the turned-off inductor current is <10 mA, 1% of the peak value of inductor current and its power consumption is no larger than traditional ones.

High efficiency DCM buck converter with dynamic logic based adaptive switch-time control

This paper presents a dynamic logic based adaptive switch-time control circuit (DASTC) for fast control to minimize body diode conduction losses and dead-time of a buck regulator operating in discontinuous conduction mode. Dead-time is an important metric for improving efficiency of low voltage converters. DASTC provides instant sensing and feedback based on the load to minimize dead-time significantly compared to prior-art and scales low side power switch pulse width adaptively across load currents, just enough to discharge the stored inductor energy fully. Furthermore, the converter has inherent pulse skipping mode to lower the switching frequency at light loads to enhance light load efficiency. The proposed 1.5 V buck regulator was fabricated in 0.35 $$\upmu$$μm CMOS process with an input voltage range of 1.8---3 V and load current range of 1---200 mA. Measurement results demonstrate a peak power efficiency of 94.6 % and a high overall power efficiency ( >~89 %) for load currents greater than 5 mA for $${V_{IN}}$$VIN = 1.8 V. The proposed scheme achieves 4× (~5 ns) better dead-time and 4---5.5 % better power efficiency compared to prior-art over the load current range.

A Nonlinear Average-Current-Controlled Multiphase Boost Converter With Monolithically Integrated Control and Low-Side Power Switches in 0.35-&lt;inline-formula&gt; &lt;tex-math notation="LaTeX"&gt;$\mu $ &lt;/tex-math&gt;&lt;/inline-formula&gt;m HV CMOS for the Automotive Sector

This paper reports the first multiphase implementation based on the recently proposed nonlinear average current control (NACC) for power-factor-correction and dc–dc converters. A multiphase boost dc–dc converter with control and low-side power switches integrated on the same die using the 0.35- $\mu $ m HV CMOS process is designed and introduced. The converter benefits from using analog current controllers that are very simple, insensitive to noise, and independent of converter and control design parameters. Multiphase operation effectively enables higher operating frequency (seen from the converter input and output), which in turn enables smaller reactive components to be selected. The converter is dedicated to supplying the electric vehicle auxiliary board net (12 V) from the photovoltaic cell stack input, allowing a maximum power of 40 W to be transferred at 500-kHz switching frequency of each phase (effectively at 1.5 MHz). Maximum power point tracking is performed as the converter global control at $\sim $ 7.5 kHz, while the inner control loops are based on NACC. Suitability of such hybrid converters for integration with active solar cells makes them favorable to be used as a solar range extender for electric/hybrid vehicles, making this a step forward toward a complete system miniaturization of solar regenerative energy solutions in automotive applications—solar-module-integrated dc–dc converters. Experimental measurements performed with a converter prototype including a chip based on 0.35- $\mu $ m HV triple-well CMOS technology verify the proposed multiphase operation and NACC control method.

A 40 V 10 W 93%-Efficiency Current-Accuracy-Enhanced Dimmable LED Driver With Adaptive Timing Difference Compensation for Solid-State Lighting Applications

This paper presents a floating-buck dimmable LED driver for solid-state lighting applications. In the proposed driver, an adaptive timing difference compensation (ATDC) is developed to adaptively adjust the off-time of the low-side power switch to enable the driver to achieve high accuracy of the average LED current over a wide range of input voltages and number of output LED loads, fast settling time, and high operation frequency. The power efficiency benefits from the capabilities of using synchronous rectifier and having no sensing resistor in the power stage. The synchronous rectification under high input supply voltage is enabled by a proposed high-speed and low-power gate driver with pseudo-digital level shifters. Implemented in a 0.35 μm 50 V CMOS process, experimental results show that the proposed LED driver can operate at 1 MHz and achieve peak power efficiency of 93% to support a wide range of series-connected output LEDs from 1 to 10 and a wide input range from 10 to 40 V. The proposed LED driver has only 2.8% current error from the average LED current of 345 mA and settles within 8.5 μs after triggering the dimming condition, improving the settling time by 14 times compared with the state-of-the-art LED drivers.

Novel high-voltage, high-side and low-side power devices with a single control signal

Novel high-voltage, high-side and low-side power devices, whose control circuits are referred to as the tub, are proposed and investigated to reduce chip area and improve the reliability of high-voltage integrated circuits. By using the tub circuit to control a branch circuit consisting of a PMOS and a resistor, a pulse signal is generated to control the low-side n-LDMOS after being processed by a low-voltage circuit. Thus, the high-voltage level-shifting circuit is not needed any more, and the parasitic effect of the conventional level-shifting circuit is eliminated. Moreover, the specific on-resistance of the proposed low-side device is reduced by more than 14.3% compared with the conventional one. In the meantime, integrated low-voltage power supplies for the low-voltage circuit and the tub circuit are also proposed. Simulations are performed with MEDICI and SPICE, and the results show that the expectant functions are achieved well.

A novel variable frequency modulation technique to improve light-load efficiency for multiphase synchronous rectified VRM

A novel variable frequency modulation technique for multiphase synchronous rectified voltage regulator module (VRM) is proposed in this paper. The proposed technique provides zero voltage switching (ZVS) for high-side and low-side power switches under both light- and heavy-load conditions, thereby increasing the efficiency as compared to the conventional approach. The dependency of switching frequency on the load condition for the proposed modulation technique and the related conduction loss are analyzed. It will be shown that the frequency increases for light-load condition in order to retain ZVS and decrease the conduction loss. Although the switching loss will slightly increase due to the increase of switching frequency, the analysis and experimental results will show that the contribution of frequency increasing can cover this additional loss. Experimental results derived from a single-phase and an eight-phase synchronous rectified VRM show that the proposed modulation technique is superior to the conventional one and compared to conventional constant switching frequency techniques with 250 and 550thinspacekHz, the efficiency can be increased up to 17 and 5% for single-phase VRM and 8 and 4% for eight-phase VRM under various load conditions. Even an off-the-shelf controller with an additional simple and cheap control circuit comprising one switch, two operational amplifiers and several resistors is used to realize the proposed technique, that is, a very low cost and small circuitry is attached to gain the significant benefit. Copyright © 2011 John Wiley & Sons, Ltd.

Non-Destructive Current Measurement for Surface Mounted Power MOSFET on VRM Board Using Magnetic Field Probing Technique

This paper proposes a nondestructive current measurement using the micro-magnetic probing technique for the surface mounted power MOSFET on VRM board to discuss the self-turn-on phenomenon. Whereas the conventional method employs a loop coil structure around the current flow, a notable feature of the proposed technique is the sensor part which is much smaller than that of conventional methods. This method designed to measure the intensity of a partial magnetic field, therefore enables the non-destructive measurement just by setting the magnetic probe on the MOSFET package. A calibration technique is introduced to reproduce current waveform and we confirm that the obtained current waveform agrees with that obtained by the conventional Current Transformer. Using the proposed technique, we succeed of detecting a shoot through current waveform of high-side power MOSFET during self-turn-on phenomenon in VRM board. We also sense non-uniform current flow among 3 parallel low-side power MOSFETs caused by board layout location. This study demonstrates the capability of sensing local transient current of VRM board.

Dead-Time Elimination of PWM-Controlled Inverter/Converter Without Separate Power Sources for Current Polarity Detection Circuit

This paper will present a dead-time elimination scheme for a pulsewidth-modulation (PWM)-controlled inverter/converter. The presented dead-time elimination scheme does not require separated power supplies for freewheeling-current detection of high- and low-side power devices. The presented scheme includes the freewheeling-current polarity detection circuit and the PWM control generator without dead time. It will be shown that the presented scheme eliminates the dead time of PWM control for inverter/converter and therefore dramatically improves output voltage loss and current distortion. Experimental results derived from a field-programmable-gate-array-based PWM-controlled inverter are shown to demonstrate the effectiveness.

The integration of high-side and low-side LIGBTs on partial silicon-on-insulator

Partial silicon-on-insulator (PSOI) is a new technology for fabricating power integrated circuits (PICs) in which the buried oxide is patterned to give silicon windows beneath the anodes of the power devices, yielding breakdown voltages and a self-heating effect comparable to those obtained in bulk silicon, yet while retaining the good isolation between the power devices and the low-power CMOS which is inherent in silicon-on-insulator [Popescu A, Udrea F, Milne W. Proceedings of CAS. 1997. p. 102–3; Lim H, Udrea F, Garner D, Milne W. Solid-State Electronics 1999;43(7):1267–80]. For a PIC, both a high-side and a low-side power device are often required. While this is possible when the power devices are LDMOSFETs [Lim H, Udrea D, Garner K, Shen K, Milne W. Proceedings of CAS. 1999. p. 149–52], high-side Lateral Insulated Gate Bipolar Transistors (LIGBTs) are difficult to fabricate in PSOI due to the unacceptably high leakage current which flows from the anodes of the LIGBTs, through the silicon window, to the substrate, and which can constitute 9.3% of the total device current. In this article, we present a novel method of eliminating that current by incorporating a deep n + diffusion between the anode of the high-side LIGBT and the silicon window. Therefore, a PSOI PIC technology is arrived at, which has everything that is required for a PIC technology: a high breakdown voltage, a similarly good self-heating effect to bulk technology, a good turn-off performance, good isolation between power devices and CMOS circuitry, and the availability of both high-side and low-side LIGBTs and LDMOSFETs.

Self-protected low-side power switchagainst abrupt current overload

The authors present a current limit, gate drive and 0.3 Ω low-side power switch circuit which provides fast current regulation (2 µs) to a preset current limit when an abrupt current overload occurs. This efficiency reduces excessive energy dissipation by the switch to prevent the switch from being burnt out.