Jian-Ru Lin

A Direct AC–DC and DC–DC Cross-Source Energy Harvesting Circuit with Analog Iterating-Based MPPT Technique with 72.5% Conversion Efficiency and 94.6% Tracking Efficiency

The proposed cross-source energy (CSE) harvesting circuit can accept universal energy sources, including AC and DC sources. The buck-boost conversion of CSE harvesting circuit automatically converts AC or DC input into DC output without being limited by universal input voltage range. CSE harvesting circuit provides dual outputs, a regulated output and a battery charging output, to optimally arrange harvest energy with 72.5% of power efficiency. A backup converter is designed to cooperate with CSE harvesting circuit to guarantee voltage stability of the regulated output. The proposed analog iterating-based (AIB) maximum power point tracking (MPPT) technique achieves 94.6% tracking efficiency without complex data calculation and storage compared to previous techniques.

12.6 90% Peak efficiency single-inductor-multiple-output DC-DC buck converter with output independent gate drive control

Single-inductor multiple-output (SIMO) DC-DC buck converters, which possess the advantage of compact size, are commonly implemented in portable electronics like mobile phones and tablets. However, their power efficiency is degraded considerably, as illustrated in Fig. 12.6.1, when multiple outputs are requested in a wide range, such as 1.2 to 3.3V for tablets. The use of P-MOSFET [1][2] and N-MOSFET [3] switches results in low efficiency of 64 and 70% at outputs of 1.2 and 3.3V, respectively, because of low gate driving voltages and large on-resistance. This implies that conventional usage of P-MOSFET and N-MOSFET switches is inappropriate in SIMO converters [1-3]. This paper presents a SIMO converter with output-independent gate drive (OIGD) control for all N-MOSFET switches. One of the salient features is that OIGD control achieves output-voltage-independent characteristics on efficiency and keeps peak efficiency of 90% over the range of 1.2 to 3.3V for tablets. The other salient feature is that a low-power deadtime overstress recycling (DOR) technique retrieves 95% of energy loss during deadtime and releases the overstress problem simultaneously.

12.7 A 96%-efficiency and 0.5%-current-cross-regulation single-inductor multiple floating-output LED driver with 24b color resolution

Lighting flicker, a rapid and repeated change over time in the brightness of light, has long been known to cause illness in humans that ranges from headaches to seizures. Thus, [1] has specified the dimming frequency, fDIM, larger than 3kHz to achieve a no-observable-effect flicker level. State-of-the-art LED drivers employ the SIMO topology with four channels in Fig. 12.7.1, to deliver energy to each LED using the time-multiplexing (TM) control technique [2-4], in which the luminance is controlled by the dimming signals. Two major shortcomings for such approaches are: (1) Sequential dimming signals; and (2) Current cross-regulation (CCR) effects. In [2], the LED drivers with TM control result in only 9b color resolution at the dimming frequency of 1.5kHz, which may cause flicker hazard. Besides, the complete white-red-green-blue (WRGB) sequence needs a total of four switching periods to light up the 4 LEDs separately. On the other hand, due to inherent rising and falling delay of the hysteretic current control (HCC) circuit, tdr and tdf respectively, the CCR effect seriously affects the accuracy of the controller when the inductor current slope is varied. For example, with L=15μH, VIN=20V, VR=2.5V, VG=3.5V, tdr=300ns and tdf=250ns, the SIMO will result in 4% CCR between Iavg,R and Iavg,G when the average LED current is 1A. More specifically, with the same color in the sequence, voltage regulation may be disregarded when regulated constant current through the sensing resistor RSEN is used as a negative feedback control. However, when different colors are in sequence, where VO, =VR, VG, VB, or VW, are different, large voltage cross-regulation (VCR) across the RSEN occurs and so does the CCR. The CCR effects become an open question for enhancing LED current accuracy. For alleviating the CCR effect, the discontinuous conduction mode (DCM) has been applied for TM control in [3]. However, with the limited output current in DCM, low output power resulted and large output capacitors were required to suppress the VCR. In this paper, a single-inductor multiple-floating-output (SIMFO) LED driver with an average-current-correction (ACC) technique is presented. The developed ACC technique is used to alleviate the CCR effect to about 0.5%. The developed LED driver using the floating output topology offers the following salient features: (1) A complete WRGB sequence is operated in only one switching cycle; (2) All LEDs can be dimmed simultaneously and each LED can also be dimmed individually to achieve 24b color resolution at fDIM=3kHz without flicker hazard; and (3) Achieving high output power and power efficiency (96%).

95% light-load efficiency single-inductor dual-output DC-DC buck converter with synthesized waveform control technique for USB type-C

The proposed single-inductor dual-output (SIDO) converter can provide wide range in duty ratio control to convert input voltage 5-20V to dual output voltages 3.3V and 1.2V when its switching frequency is raised to 10MHz for compact size solution. The proposed synthesized waveform control (SWC) technique can emulate the inductor current without being affected by switching noise. Thus, the minimum allowable duty ratio can be lowered to 6% to meet the requirement of USB-C in one-stage low duty ratio conversion. Moreover, the switching frequency is dynamically decreased by the derived DC loading information from the SWC technique. Not only the output power MOSFET but also the main power MOSFET switch in a load-dependent switching frequency for power saving. 67% more power reduction can be obtained. 95% and 83% efficiency are achieved at light and heavy loads, respectively, when the silicon is limited within 1400μm*1350μm.

Self-adjustable feed-forward control and auto-tracking off-time control techniques for 95% accuracy and 95% efficiency AC-DC non-isolated LED driver

The non-isolated buck topology for LED driver is proposed to reduce volume and cost without the need of large transformer. Besides, in the entire universal range of AC input voltage, the proposed self-adjusted feed-forward control (SAFFC) technique ensures small variation in the LED current. The auto-tracking off-time control (ATOTC) technique is also adopted to adjust the off time to guarantee the current accuracy is better than that of the peak current control (PCC) technique while and the efficiency is better than that of the hysteresis current control (HCC) technique. Test chip fabricated in VIS 0.5μm 700V ultra-high voltage (UHV) process demonstrates power factor higher than 0.97, averaged 95% high accuracy, and 95% high efficiency.

200nA low quiescent current deep-standby mode in 28nm DC-DC buck converter for active implantable medical devices

The proposed deep-standby mode (DSM) is used in 28nm power management unit (PMU) for long-term usage in active implantable medical devices (AIMD). The PMU can upgrade its normal mode with the proposed embedded auto-cancellation (EAC) technique in order to have high accuracy even if the battery is aging and the PVT variations occur. The test chip fabricated in 28nm CMOS process features low quiescent current of 200nA and output voltage accuracy of 98%. Seamless transition among the DSM and the accurate mode demonstrates both low quiescent current and high accuracy can be achieved in the proposed PMU.

A low quiescent current and cross regulation single-inductor dual-output converter with stacking MOSFET driving technique

The stacking MOSFET structure composed of low-voltage devices suffers from deteriorated transient response or large footprint area when capacitor-free or dominant pole compensation low dropout (LDO) regulator biases the driver. Due to self-stabilized feature, the proposed stacking MOSFET driving (SMD) technique effectively drives the power stage and greatly reduces noise interference from the noisy node to achieve low cross regulation (CR) in the single-inductor dual-output (SIDO) converter. Moreover, two inherent low dropout (LDO) regulators in the SMD technique completely regulate two outputs with low quiescent current at no load condition. Experimental results show the tested chip fabricated in 0.25μm process with low cross regulation of 0.015mV/mA and ultra-low quiescent current of 5μA at no load condition.

Unsymmetrical parallel switched-capacitor (UP-SC) regulator with fast searching optimum ratio technique

Different from conventional multiphase switched-capacitor (SC) DC-DC converters, the proposed unsymmetrical parallel switched-capacitor (UP-SC) regulator provides more controllable input variables to increase available conversion ratios for improved load regulation. Even under higher conversion ratio numbers, the UP-SC regulator uses the fast searching optimum ratio (FSOR) technique to search the destined ratio rapidly and to reduce the transient recovery time. Experimental results show the test chip fabricated in 0.25μm CMOS process increases the ratio number to 187 and 2389 in 3-stage and 4-stage SC regulators, respectively. Transient recovery time reduces from 26μ8 to 1.5μ8 in case of 7mA load current step.

93% Efficiency and 0.99 power factor in pseudo-linear LED driver

The proposed pseudo-linear LED driver can effectively solve the serious flicker in conventional linear LED driver (LLD). Besides, it has good electromagnetic interference (EMI) performance similar to that in conventional LLD at high AC input voltage. In the meanwhile, it has high power factor (PF) similar to boost switching regulator (SWR) LED driver at low AC input voltage. Furthermore, owing to the combination of line filter and the active full bridge rectifier, the pseudo-linear LED driver has a compact solution and high efficiency. The test chip was fabricated in 0.5μm 500V LDMOS process. Experimental results show 93% high efficiency, 6% total harmonic distortion (THD), and 0.99 PF at the power of 7W.

Ultra-low voltage ripple in DC-DC boost converter by the pumping capacitor and wire inductance technique

Overall consideration including bonding wire effects is needed because conventional DC-DC boost converter used in energy harvesting systems suffers from large output voltage ripple in steady state and transient response. Thus, this paper proposed the pumping capacitor and wire inductance (PCWI) technique to suppress output voltage ripple to an ultra-low value. Small steady state voltage across the wire inductance (WI) and continuous WI current can be ensured by an additional pumping capacitor (PC). Moreover, even in case of an ultra-low output voltage ripple, the proposed pseudo-inductor current (PIC) technique regenerates the inductor current information to eliminate the instability problem in conventional ripple-based control techniques. Transient recovery time and output voltage variation can be reduced simultaneously. Test chip was fabricated in 0.18-μm 5V/24V CMOS process when input voltage of 1.8–5.5V is converted to 12.8V. Experimental results show the ratio of output voltage ripple and output voltage is reduced to 0.04%. Measured power conversion efficiency is around 92% at 100mA and 96% at 0.1mA.