Date

2018

Author

Kılıç, Emrecan

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Design of efficient and compact switch-mode power supplies (SMPS) is a popular topic in power electronics. Silicon has been used as semiconductor material of switches in DCDC converters for decades. However, preference of using GaN as semiconductor material of switches in these topologies has recently increased due to their superior properties. GaN FETs have lower gate capacitance, lower channel resistance, higher frequency operation, higher breakdown voltage and higher temperature operation than silicon MOSFETs. Those properties provide increase in the efficiency of DC-DC converters and reduction in the size of filter components of them. This thesis focuses primarily on developing an efficient DC-DC converter, and secondly a compact converter. Design of a low-power and radiation hardened PWM (Pulse Width Modulation) controller has helped the DC-DC converter in this thesis has a high efficiency. In order to increase efficiency further, GaN devices have been used as switches because they have lower gate capacitance and channel resistance, which means lower switching and conduction losses, than those of silicon MOSFETs. On the other hand, using GaN FETs has enabled working at high frequencies in order to reduce the size of filter components and producing a compact DC-DC converter as required in most of the applications today. The PWM controller has been designed as integrated circuit, manufactured and tested. 0.18 µm SOI (Silicon-On-Insulator) technology has been used throughout the design. The PWM controller is a current mode controller and has internal blocks which are error amplifier, SR latch, clock generator, voltage reference, current sense and inverter. Error amplifier is designed with 83.8° phase margin in order to have a stable DC-DC converter. Clock of the controller is implemented by a ring oscillator with a duty cycle adjustment circuit whose output gives a clock with duty cycle of %32 and frequency up to 10 MHz. Furthermore, it has an external pin through which an external clock signal might be given. A reference voltage of 1.27 V is produced in order to compare it with the output of the current sense block. A delay generation circuit has been designed by using inverters, which provides reduction of switching losses. Experimental results show that the PWM controller is able to drive a GaN FET, whose input capacitance is 588 pF, at 10 MHz. At this condition, the PWM controller is supplied with 5 V, and it has a power dissipation of 15 mW. Efficiency of the DC-DC converter is measured as 83.1% with 3.2 VDC input. The converter also gives 3 VDC output at 100 mA load with 30 VDC input voltage in a closed loop configuration. The circuit shows stable operation under full-load to no-load transition. The PWM controller chip size is 2.5mm x 3mm. The controller is radiation hardened thanks to the internal resistance of SOI technology.

Subject Keywords

PWM power converters., Switching power supplies., Electric current converters.

URI

http://etd.lib.metu.edu.tr/upload/12622580/index.pdf
https://hdl.handle.net/11511/27517

Collections

Graduate School of Natural and Applied Sciences, Thesis