Design and development of 1 KW solid state RF amplifier

Transcription

1 Journal of Physics: Conference Series Design and development of 1 KW solid state RF amplifier To cite this article: Gayatri Ashok et al 2010 J. Phys.: Conf. Ser View the article online for updates and enhancements. Related content - Design aspects of 13.56MHz, 1kW, CW- RF oscillator for plasma production Sunil Kumar, Bhavesh Kadia, Raj Singh et al. - Automatic impedance matching network for ICRH-RF experiments on SST-1 R Joshi, M Singh, H M Jadav et al. - Conceptual design of automation of ICRH vacuum system on Aditya Tokamak Dharmendra Rathi, Kishore Mishra, Ramesh Joshi et al. This content was downloaded from IP address on 21/12/2017 at 23:36

2 Design and development of 1 KW Solid State RF amplifier Gayatri Ashok, Bhavesh Kadia, Pragya Jain, S.V Kulkarni and ICRH-RF Group. 1 Institute for Plasma Research,Bhat, Gandhinagar, gayatri@ipr.res.in Abstract. Since low power tube based RF amplifiers are complicated, occupy a large space and are bulky, the efforts are on to develop indigenously 1 KW solid state technology based RF Power amplifier. A power level of 1KW is chosen for the initial design because RF power Mosfets upto 250 watt are easily available and by clubbing 3-4 stages the power level of 1 KW can be made. Presently design and testing of 100-watt stage is in progress. The first 2 stages are designed to give 5 Watt RF power using bipolar transistors and are operated in CE, Class A to provide low noise level at the output of the system. The 3 rd stage will be MOSFET based MRF 174, which is ideally suited for class A operation and is designed for 100 Watt RF power. The last stage will be MOSFET based ARF446 power MOSFET in TO-247 plastic package. This amplifier will be used in the classical push- pull configuration. This paper describes the design aspects as well as the test results of 100 watt amplifier on 50 Ohm dummy load along with the specifications, design criteria,circuit used, operating parameters of 1 KW Solid State RF power amplifier to be used as driver for 91.2 MHz, 1.5 MW stage for ICRH experiments on SST-1 tokamak. c 2010 Ltd 1

3 1. Introduction Ion cyclotron resonance heating is one of the auxiliary heating schemes for tokamak plasmas. For raising the temperature of the Ohmically heated plasma in SST-1.Tokamak from 200 ev to 400 ev under the existing values of plasma parameters and magnetic fields 1 MW of RF power is required. Our present design involves the development of 1KW RF solid state amplifier which will be a pre-driver stage for 1.5 MW at 91.2 MHZ. Certain design objectives were kept in mind while deciding the outlines and the type of circuits. The circuits would be chosen in such a way that cost and complexity of the circuit is optimized. Simple and conventional devices would be selected to ensure availability and replacement. Proven and latest possible technology would be used to provide reliability, ease in selection of material and fabrication. System would be protected against all possible faults and failures. Operator s safety would be kept in mind while making the layout of the system. Under normal operation or during condition of fault the system should not harm or damage other systems of SST-1. System should be electrically and mechanically compatible the requirements of SST-1. 2.Block diagram representation: FUNCTION GENERATOR OF 500mW STAGE - I OF 5W STAGE - II OF 100W STAGE III 50 Ohm LOAD OF 1KW STAGE V OF 500W STAGE IV Figure1. Block diagram representation of all stages 2

4 Fig 1 shows the block diagram of the amplifier stages. The first stage is transistor based and transistor 2n3866 has been used. Input matching network is used to couple the power to the base of the transistor from signal generator. Output matching network delivers 500mW power to the gate of MRF174.Biasing resistors R1 and R2, R3 and R4 are used to provide the base voltage to 2n3866 and MRF174 of the II nd stage.supply voltage is kept at 24 volts. RF power from the output of II nd stage is efficiently coupled to the III rd stage. (Refer figs.2,3,4,5). Figure 2. Circuit diagram of I st and II nd stage 3

5 Figure 3.Circuit diagram of III rd stage The first 2 stages have been tested upto 5 watt and the output power has been observed. All the remaining stages have been designed and are in the testing phase. The voltage waveforms are as shown in figures 6,7,and 8. Figure 4: Photograph of the developed 500mW stage. Figure 5: Photograph of the developed 5W stage. 4

6 500mV/div,5ns/div 2.2 V/div,5ns/div Figure 6: Input voltage waveform at the base of stage-i Figure 7:Output voltage waveform of stage-i Figure 8: Output voltage waveform of stage-ii 5

7 Conclusions and references: Indigenous development of 1KW solid state RF power amplifier is planned.the first 2 stages upto 5 watt has been tested and the output power has been observed.all the remaining stages are in the design phase. References: [1] Richard Frey,P.E.High Voltage,high efficiency Mosfet RF amplifiers-design procedure and examples(advanced power technology) [2] B.Becciolini Impedance matching networks applied to RF power transistors (Motorola semiconductor application note) [3] James K.Hardy High Frequency Circuit design 6