In this work we demonstrate a synchronous bootstrap power delivery scheme applied to a high level count GaN-based flying capacitor multi-level (FCML) converter. The proposed approach is well suited for high-frequency operation as it eliminates conventional boot-strap diodes and allows for precise on-time control for a maximized conduction duration. Importantly, we note the synchronous boot-strapping scheme's capability for bi-directional energy transfer: Gate driver power can be injected into the chain from either a ground referenced supply, a high-side line referenced supply, or both simultaneously for further reduced voltage droop. A discrete 6-level FCML hardware prototype switching at 500 kHz (2.5 MHz effective) is designed and constructed to validate this approach. A maximum deviation in supply voltage of 156 mV throughout all 10 series stacked gate drivers for converter duty ratios spanning 15-85% is measured. Subsequently the need for local regulation throughout the gate-drive chain is eliminated, which in turn improves efficiency, simplifies design, and reduces cost.

In this work, we present a robust gate drive power delivery approach well-suited for converter topologies, such as the flying-capacitor multi-level (FCML) converter, that contain several series-connected switching elements. The proposed power delivery network leverages internal voltages inherent to the FCML topology in combination with a charge-pump mechanism to provide gate drive power with high efficiency. The charge-pump design operates independently of the primary switching devices, allowing the converter to operate at very low duty ratios without suffering from significant degradation of the floating supplies. The concept is validated in a hardware prototype, demonstrating an estimated 38% reduction in gate drive power delivery losses compared to competing techniques. Moreover, the robustness of the technique is validated through incorporation into a 400V, 2kW 6-level FCML DC-DC converter, achieving a 99.07% peak conversion efficiency and 2.05kW/in power density.

Targeting neurons with light-driven opsins is widely used to investigate cell-specific responses. We transfected midbrain dopamine neurons with the excitatory opsin Chrimson. Extracellular basal and stimulated neurotransmitter levels in the dorsal striatum were measured by microdialysis in awake mice. Optical activation of dopamine cell bodies evoked terminal dopamine release in the striatum. Multiplexed analysis of dialysate samples revealed that the evoked dopamine was accompanied by temporally coupled increases in striatal 3-methoxytyramine, an extracellular dopamine metabolite, and in serotonin. We investigated a mechanism for dopamine-serotonin interactions involving striatal dopamine receptors. However, the evoked serotonin associated with optical stimulation of dopamine neurons was not abolished by striatal D1- or D2-like receptor inhibition. Although the mechanisms underlying the coupling of striatal dopamine and serotonin remain unclear, these findings illustrate advantages of multiplexed measurements for uncovering functional interactions between neurotransmitter systems. Furthermore, they suggest that the output of optogenetic manipulations may extend beyond opsin-expressing neuronal populations.

Many voltammetry methods have been developed to monitor brain extracellular dopamine levels. Fewer approaches have been successful in detecting serotonin in vivo. No voltammetric techniques are currently available to monitor both neurotransmitters simultaneously across timescales, even though they play integrated roles in modulating behavior. We provide proof-of-concept for rapid pulse voltammetry coupled with partial least squares regression (RPV-PLSR), an approach adapted from multi-electrode systems (i.e., electronic tongues) used to identify multiple components in complex environments. We exploited small differences in analyte redox profiles to select pulse steps for RPV waveforms. Using an intentionally designed pulse strategy combined with custom instrumentation and analysis software, we monitored basal and stimulated levels of dopamine and serotonin. In addition to faradaic currents, capacitive currents were important factors in analyte identification arguing against background subtraction. Compared to fast-scan cyclic voltammetry-principal components regression (FSCV-PCR), RPV-PLSR better differentiated and quantified basal and stimulated dopamine and serotonin associated with striatal recording electrode position, optical stimulation frequency, and serotonin reuptake inhibition. The RPV-PLSR approach can be generalized to other electrochemically active neurotransmitters and provides a feedback pipeline for future optimization of multi-analyte, fit-for-purpose waveforms and machine learning approaches to data analysis.

This work presents a distributed regenerative snubber network with reduced part count in multi-level converter designs. The proposed technique utilizes the ordinarily detrimental parasitic commutation loop inductance to harvest COSS-related energy using a network of high-speed diode-capacitor catching circuits. The proposed approach has several attractive features: First, VDS overshoot is greatly reduced, as with conventional snubber design. Second, the speed of switching transitions may be increased substantially for reduced overlap loss. Third, layout design effort is relaxed, with larger commutation loop geometries expected to improve system performance. Fourth, a soft-charged daisy-chain allows multiple snubbers to sequentially transfer harvested energy to a common collection point with high efficiency. Finally, a single active component is used to resonate recovered energy back into the primary power path resulting in increased converter efficiency. A hardware prototype demonstrates intended operation in a 6-level flying capacitor multilevel (FCML) converter, with measured waveforms illustrating further improvement with modified active balancing control.

The series-capacitor buck (SCB) converter is a compact and highly-efficient alternative to the multi-phase buck converter and has recently been demonstrated in data center applications. To achieve high power density, it is desirable to reduce the total flying capacitance in this topology. However, for sufficiently small flying capacitances, a discontinuous capacitor voltage mode (DCVM) manifests, leading to an imbalance in inductor currents. This work provides a detailed derivation of the relationship between the critical capacitance describing the onset of DCVM and converter operating parameters. Moreover, the inductor current imbalance is characterized through the development of a clamped steady-state model. To recover balancing when flying capacitance below the critical value is used, a technique to drive the branches with modified duty cycles in a constant power regime is proposed. Experimental validation of the steady-state model and recovery of inductor current balancing are demonstrated on a 4-branch SCB prototype.

Areas of low voltage electrograms (<0.5 mV) (LVA) are known to correlate with areas of atrial fibrosis and are related to clinical outcomes after ablation. We hypothesized that delay in seeking invasive treatment is linked to larger LVA.