title: Supercapacitor-based linear converter for voltage regulator modules

authors: Wickramasinghe, Thilini Chintha Prabha Kumari

subjects: DC-DC converter

abstract: This thesis investigates a linear converter technique suitable for microprocessor voltage regulator modules (VRMs). The original linear regulator is the patented supercapacitor assisted low-dropout regulator (SCALDO). A less complex, lower cost design was achieved by reducing the number of switches in the original SCALDO and adding a second low dropout regulator (LDO).
In the initial implementation of this reduced-switch SCALDO (RS-SCALDO), output regulation failed due to the presence of a parasitic body-diode in standard LDOs. The body-diode forms an unwanted discharge path to ground for the supercapacitor. In order to block this path, an application specific LDO that operates in the third quadrant of a MOSFET current-vs-voltage transfer function was investigated.
A 3.5-to-1.5 V RS-SCALDO was designed with a supercapacitor, two LDOs and two switches. Compared with the standard SCALDO approach, this new design halves the number of switches required. Discrete MOSFET-based high-current LDOs were developed and combined with a common feedback control circuit. Voltage identification (VID) capability was implemented using a digital potentiometer. Theoretically, when an LDO converts 3.5 V to 1.5 V a maximum efficiency of 1.5/3.5(~43%) can be achieved. According to the general theory of SCALDO, a single supercapacitor configuration can achieve nearly twice the linear regulator efficiency. The 3.5-to-1.5 V, 5 A RS-SCALDO achieved an approximate end-to-end efficiency of 80%, thus, agreeing with SCALDO general theory.
Large-signal analysis was used to model MOSFET non-linearities and predict the performance of LDOs, switches and the overall system. Matlab  modeling predictions for body-diode behaviour were cross-checked via SPICE simulation; the results agreed with bench measurements.
RS-SCALDO regulators cycle at very low frequencies, usually in the range of millihertz to hertz. Therefore, electromagnetic interference emitted by high-frequency switched-mode VRMs is not an issue here. Compared to typical high-frequency VRMs, RS-SCALDO topology provides similar efficiencies with the high slew-rate and low noise output of a linear regulator. In generalized SCALDO configuration with n supercapacitors, a total of 3n+1 switches required; in contrast RS-SCALDO reduces the switch count to 2n. With the elimination of the body-diode parasitics, the technique can be extended to much higher currents.

text: Supercapacitor-based linear converter for voltage regulator modules This thesis investigates a linear converter technique suitable for microprocessor voltage regulator modules (VRMs). The original linear regulator is the patented supercapacitor assisted low-dropout regulator (SCALDO). A less complex, lower cost design was achieved by reducing the number of switches in the original SCALDO and adding a second low dropout regulator (LDO).
In the initial implementation of this reduced-switch SCALDO (RS-SCALDO), output regulation failed due to the presence of a parasitic body-diode in standard LDOs. The body-diode forms an unwanted discharge path to ground for the supercapacitor. In order to block this path, an application specific LDO that operates in the third quadrant of a MOSFET current-vs-voltage transfer function was investigated.
A 3.5-to-1.5 V RS-SCALDO was designed with a supercapacitor, two LDOs and two switches. Compared with the standard SCALDO approach, this new design halves the number of switches required. Discrete MOSFET-based high-current LDOs were developed and combined with a common feedback control circuit. Voltage identification (VID) capability was implemented using a digital potentiometer. Theoretically, when an LDO converts 3.5 V to 1.5 V a maximum efficiency of 1.5/3.5(~43%) can be achieved. According to the general theory of SCALDO, a single supercapacitor configuration can achieve nearly twice the linear regulator efficiency. The 3.5-to-1.5 V, 5 A RS-SCALDO achieved an approximate end-to-end efficiency of 80%, thus, agreeing with SCALDO general theory.
Large-signal analysis was used to model MOSFET non-linearities and predict the performance of LDOs, switches and the overall system. Matlab  modeling predictions for body-diode behaviour were cross-checked via SPICE simulation; the results agreed with bench measurements.
RS-SCALDO regulators cycle at very low frequencies, usually in the range of millihertz to hertz. Therefore, electromagnetic interference emitted by high-frequency switched-mode VRMs is not an issue here. Compared to typical high-frequency VRMs, RS-SCALDO topology provides similar efficiencies with the high slew-rate and low noise output of a linear regulator. In generalized SCALDO configuration with n supercapacitors, a total of 3n+1 switches required; in contrast RS-SCALDO reduces the switch count to 2n. With the elimination of the body-diode parasitics, the technique can be extended to much higher currents.

year: 2016

title: Design enhancements of the smart sediment particle for riverbed transport monitoring

authors: Kularatna-Abeywardana, Dulsha

subjects: environmental monitoring

abstract: This paper discusses new enhancements that are being made to the existing ‘Smart Sediment Particle’. The smart sediment particle has been designed and implemented to track its own 3-dimensional trajectory when placed in a riverbed. This device serves as a tool to detect sedimentation in rivers. The device has been developed over the years, with its size diminishing significantly down to a sphere of 2cm radius. The readings obtained from the pebble are accurate and match well with other independent motion sensor readings. Currently a novel IPT (Inductive Power Transfer) based power supply is being integrated to this device, to charge it wirelessly, when it has been extracted from the water. A new low power, miniaturized microcontroller has been introduced to minimize the power consumption and the PCB real estate of the device. The paper discusses these new enhancements in detail and also other potential enhancements such as error compensation and wireless data transfer.

text: Design enhancements of the smart sediment particle for riverbed transport monitoring This paper discusses new enhancements that are being made to the existing ‘Smart Sediment Particle’. The smart sediment particle has been designed and implemented to track its own 3-dimensional trajectory when placed in a riverbed. This device serves as a tool to detect sedimentation in rivers. The device has been developed over the years, with its size diminishing significantly down to a sphere of 2cm radius. The readings obtained from the pebble are accurate and match well with other independent motion sensor readings. Currently a novel IPT (Inductive Power Transfer) based power supply is being integrated to this device, to charge it wirelessly, when it has been extracted from the water. A new low power, miniaturized microcontroller has been introduced to minimize the power consumption and the PCB real estate of the device. The paper discusses these new enhancements in detail and also other potential enhancements such as error compensation and wireless data transfer.

year: 2009

title: Reha Aperahama: a Ngati Rahiri rangatira

authors: Hart, Philip

abstract: Reha Aperahama had an illustrious whakapapa and was affiliated to several hapu. His father was notable as one of the most loyal rangatira (from the Crown’s perspective) in Hauraki, and Reha followed his lead, probably in part because of the financial rewards he received from selling land to settlers. He tried to maximize his income from this source, spending several years pleading for permission to sell his Te Kawana block (near Te Aroha). After opposing Ngati Haua ambitions to acquire the Aroha block, by 1878 he was willing to encourage road building. 
Reha was regularly before the courts because of his inability or reluctance to pay his debts, occasionally perjuring himself to avoid liability. In his later years he had little money. Despite occasionally being drunk and even violent, he was an important figure in Maori society, with a leadership role in his hapu and in the Mormon church. He was also notable for his marital complications.

text: Reha Aperahama: a Ngati Rahiri rangatira Reha Aperahama had an illustrious whakapapa and was affiliated to several hapu. His father was notable as one of the most loyal rangatira (from the Crown’s perspective) in Hauraki, and Reha followed his lead, probably in part because of the financial rewards he received from selling land to settlers. He tried to maximize his income from this source, spending several years pleading for permission to sell his Te Kawana block (near Te Aroha). After opposing Ngati Haua ambitions to acquire the Aroha block, by 1878 he was willing to encourage road building. 
Reha was regularly before the courts because of his inability or reluctance to pay his debts, occasionally perjuring himself to avoid liability. In his later years he had little money. Despite occasionally being drunk and even violent, he was an important figure in Maori society, with a leadership role in his hapu and in the Mormon church. He was also notable for his marital complications.

year: 2016