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| Transistor mystery | ||
| Author naoge Views 4 Posted at 2008/8/26 05:17 [View In Forum] | ||
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How are transistors selected for various practical circuits.pwxy pwxy pwxy Say i want to design a amplifier how do i begin.pwxy pwxy pwxy How to choose bias and various r and c values ?pwxy pwxy pwxy pwxy pwxy pwxy What can be a check for transistor working in active mode and how can the gain be calculated ?pwxy pwxy pwxy pwxy pwxy pwxy Fuh !! lots of question in on stroke !!!! but can' t help it ,i am dying to understand the working of practical transistor circuits.pwxy pwxy pwxy pwxy pwxy pwxy Thanks !! |
| Reply No. | Replier | Total Replies 16 [View All Replies] [New Reply] | Replied at |
| 1 | edu | Transistor mystery Please check any basic electronics books. Milman Halkias is good. In our forum : Teach yourself electronics and electrical is also good as a beginer guide. |
2008/8/26 05:17 |
| 2 | chdd | Transistor mystery As far as the transistor selection you need the Ft value to be greater than the gain x bandwidth of the circuit. Then price and availability further constrict your selection. Then there are specialized needs that dictate JFET or MOSFET as the active device even though they cost more than BJT. Then you select the bias point. The transistor data sheet will tell you what you gain and lose for various values of current and voltage. Then you select the bias circuit. The temperature range and variation of transistor DC parameters between production lots will determine the details of the part values. Then you select the remaining parts for the frequency response and gain you need. Since you seem to be aiming to a hobby circuit and probably do not have a lot of expensive, high performance test equipment, I would suggest the 2N2222 and its variations as a good first try for your circuit. It is not a microwave transistor and so if your circuit self oscillates, you can catch it on an ordinary oscilloscope. The Ft is 750 MHz or so and the performance will be adequate for most amplifiers you make. |
2008/8/26 05:17 |
| 3 | htc2498 | Transistor mystery hi guy, i used to deal with β of the transistor as a coinstant, but when i downloaded a data sheet for the 2N3904 ifound that : there is alot of values β , and all of them depends mainly on Ic, i tried to draw these values to make a charachteristic curves but i shoched when i found it produce nonlinear amplification. is there anyone can explain this to me???????????????????????? [/size |
2008/8/26 05:17 |
| 4 | netlgc | Transistor mystery Yes, the BJT is a very nonlinear device. That is why it is for small signals in the common emitter configuration. Adding feedback in the form of an unbypassed emitter to ground resistor helps a lot. If you want further linearity, use feedback around two stages. The JFET is more linear but costly. If you want larger signals to be linear you will have to use valves/tubes with a 300 V power supply so the signal is a small fraction of the 300 V. |
2008/8/26 05:17 |
| 5 | spacebac | Transistor mystery http://www.allaboutcircuits.com/vol_3/chpt_4/1.html this is a good book for BLT Added after 6 seconds: |
2008/8/26 05:17 |
| 6 | gao51755775 | Transistor mystery Hi, You can also download some SPICE simulator and simulate the general purpose transistor models in the program that you can buy locally, it will help you learn and test the theory of biasing after some self reading on biasing. Also, it will give you a good estimation of biasing resistor values not to mention save you a lot of time messing around building circuits that don't work. Good luck! You can find some freeware SPICE on the forum, just go to the download sofware section. |
2008/8/26 05:17 |
| 7 | mxg330 | Transistor mystery if u want to strengthen ur knowledge in bjts u have to read millman and halkias its THE best resource available... u might find certain things too hi funda at first but keep reading and re reading ..its totally worth it |
2008/8/26 05:17 |
| 8 | wy830115 | Transistor mystery As the questions you posted are quite fundamental, I would suggest you begin with some popular analog IC design books, such as Ken Martin's Analog Integrated Circuit Design or Razavi's book. Typically you need to understand why the transistor needs to work in different regions, what is the principle behind the amplifier design, the purpose of circuit biasing, etc. It is not practical for anyone to address these issues in this single email. |
2008/8/26 05:17 |
| 9 | zunwang | Transistor mystery select transistor based on the gain u want. hfe is the most important thing in the selection of transistors |
2008/8/26 05:17 |
| 10 | ct731 | Transistor mystery transistors are mainly used for two purposes 1. switching 2. amplification in either case the main parameters that govern the selection of transistor is collector current, power disipatted, collecter to emitter volatage, collector to base voltage, gain factor beta etc. |
2008/8/26 05:17 |
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