الفهرس 
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Abstract
The aim of the present thesis is to shed further light on a comparative study of some applications (switch, RC- phase shift oscillator and DC-DC converter: boost and reverse self lift N/O Luo), based on two of the most common active electronic devices: bipolar junction transistors (BJTs) and metal oxide semiconductor field effect transistors (MOSFETs), under the influence of different operating conditions (high temperature ranging from room temperature up-to 135 oC and gamma radiation up-to almost 16 kGy).
In this respect, extensive studies, and experimental works, were carried out on the tested devices; BJT type 2SC2120 connected in the common emitter configuration (CEC) and N-channel Enhancement Mode MOSFET type 2N6660. As well, for designing and implementing the proposed application circuits, a computer simulation using National Instrument Multisim Program Version 13.0 was applied.
In this regard, the study includs the following:
First: A detailed study of the electrical charactersics
The static (I-V) characterstic curves (input / output for BJT, and transfer/output for MOSFET) were plotted. Besides, the dynamic characteristic curves, (C-V), namely: diffusion CD / transition CT capacitances, as well quality Q and - dissipation D -factors, and device impedance Z and phase angle ϕ for the two tested devices.
from the static characterstic curves of the tested devices, several electrical parameters were calculated, at normal conditions, as well, under the infleunce of different environmentanl conditions.
Concerning BJT, its DC current gain (hFE) value was calculated to be 79.4, calculated at room temperature and 240, at 85 oC, while its value was shown to be decreased down to 13, at 5.0 kGy. In Addition, for higher temperature levels, up-to 135 oC and gamma radiation doses up-to 16 kGy, a noticeable saturation in hFE was observed.
Cosidering MOSFET, a noticeable decrease in the drain current from an initial value of 0.22 A, measured at 55 oC, while its value was shown to be increased up-to 0.86 A, whenever exposed to 8.0 kGy of gamma radiation.
Second: Designing and implementation of different application circuits
The electrical parameters of the different application circuits for both devices, were recorded and plotted either at the normal or different environmental conditions.
• Switching circuit:
The design of switching circuit operated at switching frequency (fs)
of 40 kHz, input signal amplitude of 2.5 V and bias voltage of 5.0 V was carried out, and the effect of the environmental conditions on the swich transient times was studied.
Concerning BJT, the switching transient times (rise time, fall time, delay time were measured at normal conditions to be 0.95, 0.48, 0.27μs, respectively. While, during the system application at elevated temperature levels, up-to 85 oC, their values reached 1.36, 0.66 and 0.6 μs, respectively. On the other, when exposed to gamma dose up-to 16 kGy, the differet mentioned transient times were shown to be decreased down to 0.84, 0.36 and 0.18 μs, respectively. While, it was observed that for the different environmental conditions, the storage time was shown to be constant.
On the other hand, the same switching transient times for MOSFET switch were measured at normal conditions to be 0.9, 0.38 and 1.32 μs, respectively. But, as it operates at high temperature up-to 135 oC, the previously mentioned transient times were shown to be increased up-to 1.36, 0.6 and 1.02 μs, respectively. While, it was observed that for the different environmental conditions, the storage time was shown to be constant.
• RC- phase shift oscillator:
The study was extented to include the operation of a sinsoidual RC-phase shift oscillator under the mentioned environmental conditions. where studing the pk-pk voltage value of the output signal and frequency of the oscillator circuit, insures that a noticable decrease in their values was observed whenever either BJT or MOSFET was used. In addition, gamma irradiation causes an increase in pk-pk voltages of the output signals applying BJT, while decreasing in its value whenever MOSFET was used. On the other hand, for both devices, the oscillation frequency was shown to be decreased.
Concerning BJT, the value of pk-pk voltage was decreased by ratio 33.7 % of its initail value, whenever it operates at elevated temperature of 135oC, while the oscillation frequency was shown to be decreased by a ratio of 3.9 %. On the other hand, whenever exposed to gamma radiation up-to 16 kGy, the value of pk-pk voltage was increased by ratio 21.8 %, while the frequency decresed by 20.9 %.
Concerning MOSFET, the value of pk-pk voltage and oscillation frequency were shown to be decreased by a ratio values of 46.2 and 2.07 %, respectively, whenever the device operates at a temperature of 135oC. On the other hand, whenever exposed to gamma radiation up-to 3.5 kGy, the pk-pk voltage and oscillation frequency were shown to be decreased by ratio 90 % and 54.9 %, respectively.
• DC-DC converters:
The thesis was extended to include the study of two types of DC-DC converters, based on the investigated two devices (BJT/MOSFET), as a switch element during the converter operation at the three modes, namely: discontinous, critical and continous- conduction modes (DCM, CrCM and CCM) . In this concern, DC-DC boost- and reverse self-lift N/O Luo- converter were designed, implemented and studied including; measuring of DC output voltage, output voltage ripple, as well spike voltage, parasitic ringing freaquency and pk-pk voltage value at the switch node, whenever BJT/MOSFET switches exposed to the previously environmental conditions.
The experimntal results showed that, for the different operating modes the output voltage of the reverse self-lift N/O Luo converter was higher than that of the boost converter. Also, disappearance of the parasitic ringing frequency at the switch node was observed, whenever the converter operated at the discontinous conduction mode. Where, it is type of converters with voltage lift technique which characterised by; high output voltage with lower ripples, and lower parasitic effects.
The results showed that, slight decrease in the output voltage of the boost converter by ratio of 1.88% and 2.08%, for DCM and CrCM, respectivey, using BJT as a switch element. While, for CCM the output voltage was almost constant during the operating temperature range. In addition, when MOSFET was used, the values of the output voltage was shown to decreased by a ratio values of 1.85%, 4.0% and 2.12 % for the different modes, respectively.
Moreover, for reverse self-lift N/O DC-DC Luo converter, the output voltage values were shown to be decreased by a ratio values of 0.8% and 3.8 % for DCM and CrCM, respectively. While, for CCM its value was almost constant. In addition, when MOSFET was used, the values of the output voltage was a decreased by ratios of 1.69 and 1.9 % for DCM and CrCM, respectively. While, for CCM its value was almost constant
Furrhermore, when BJT device exposed to gamma radiation a slight increse in the output voltage value of the boost converter by ratio of 2.83%, 2.08% and 4.3% for DCM, CrCM and CCM, respectively. Whlie, whenever MOSFET device was applied, the previously mentioned values were shown to be increased by 1.85%, 2.0% and 2.12 % for the different operating modes, respectively. In addition for the reverse self left Luo converter, the output voltage for BJT increased by ratio of 0.86 % , 1.92 % and 2.08 % for DCM, CrCM and CCM respectively. where when MOSFET device used as a switch, the perviously mentioed values were shown to be increased by ratio of 0.84 % , 1.92 % and 2.08 % for DCM, CrCM and CCM respectively.
Third: Computer simulation was applied using National Instrument Multisim Program Version 13.0 for designing and testing the different applications based on proposed devices.