Leaf senescence can be triggered by a high availability of carbon relative to nitrogen or by external application of abscisic acid (ABA). Most Arabidopsis mutants with decreased sugar sensitivity during early plant development are either ABA insensitive (abi mutants) or ABA deficient (aba mutants). To analyse the interactions of carbon, nitrogen and ABA in the regulation of senescence, wild-type Arabidopsis thaliana (L.) Heynh. and aba and abi mutants were grown on medium with varied glucose and nitrogen supply. On medium containing glucose in combination with low, but not in combination with high nitrogen supply, senescence was accelerated and sucrose, glucose and fructose accumulated strongly. In abi mutants that are not affected in sugar responses during early development (abi1-1 and abi2-1), we observed no difference in the sugar-dependent regulation of senescence compared to wild-type plants. Similarly, senescence was not affected in the sugar-insensitive abi4-1 mutant. In contrast, the abi5-1 mutant did exhibit a delay in senescence compared to its wild type. As ABA has been reported to induce senescence and ABA deficiency results in sugar insensitivity during early development, we expected senescence to be delayed in aba mutants. However, the aba1-1 and aba2-1 mutants showed accelerated senescence compared to their wild types on glucose-containing medium. Our results show that, in contrast to sugar signalling in seedlings, ABA is not required for the sugar-dependent induction of leaf senescence. Instead, increased sensitivity to osmotic stress could have triggered early senescence in the aba mutants.
International audienceAn isolated active-clamp flyback power supply with a new resonant operation mode is designed and experimentally tested. A full soft-switching design based on dead-time optimization new approach is implemented. Each topology phase is detailed. An experimental board is presented for high ambient temperature (200 °C) operation. The power supply is dedicated to provide the driver power of wide bandgap power components in a phase-leg configuration. The constraint for galvanic isolation is high and guides the design of the transformer. The power-supply capabilities are 15 V input voltage, 6 V output voltage, 2 W output power, 75% peak efficiency, 11 cm2 footprint, and nominal operation at 200 °C ambient temperature
International audienceA PCB embedded transformer for harsh environment (i.e., ambient temperature above 200 • C) applications is presented and used in the design of a 2 MHz integrated power-supply prototype for gate driver. The main benefits of using this developed PCB embedding process are the capability to customize the air-gap for the flyback transformer and volume reduction for the converter. The easy modulation of the air-gap distance can be achieved using PCB material in specfic thickness. Moreover, the design of a coplanar-winding transformer structure with very low inter-winding capacitance needs a large winding area and raises the interest for the PCB integration approach. Two-machined ferrite pieces in UI shape were sandwiched into a multi-layer PCB laminate with multiple pressing processes. A converter prototype built with the PCB embedded transformer and other components (GaN transistors, gate driver and passives) mounted above it shows 72% of power efficiency. One thousand thermal cycles between −55 • C and 200 • C were performed on the PCB embedded transformer without observation of any major defects, such as delamination and cracking. The thermal reliability test validates the compatibility between the selected ferrite core and PCB materials as well as the feasibility of this developed transformer embedding method. A three-time volume reduction is achieved when comparing with a benchmark converter prototype using discrete transformer
With fast power semiconductor devices based on GaN and SiC becoming more common, there is a need for improved driving circuits. Transformers with smaller interwinding capacitance in the isolated gate drive power supply helps in reducing the conducted EMI emission from the power converter to auxiliary sources. This paper presents a transformer with a small volume, a low power loss and a small intercapacitance in a gate drive power supply to fast switching devices, such as GaN HEMT and SiC MOSFET. The transformer core is embedded into PCB to increase the integration density. Two different transformer designs, the coplanar-winding PCB embedded transformer and the toroidal PCB embedded transformer, are presented and compared. The former has a 0.8 pF inter-capacitance and the latter has 85% efficiency with 73 W/in 3 power density. Both designs are dedicated to a 2 W gate drive power supply for wide-band-gap device, which can operate at 200 C ambient temperature.
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