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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Emitter Follower
HEllo Guys,
I am trying to design a Emitter Follower. I am trying to give the load resistance as 50 Ohm. Could some one tell me how to calculate the Biasing resistance on the Base circuit of the transistor.I am assuming that the Short circuit current gain (Beta = 100). I am using a npn 2n2222a transistor for my purpose. Voltage supply on the collector is 12V. Voltage supplied to the base is from the output of a sound card or a signal generator.So please help me in getting the answers Regards Nitin |
#2
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Emitter Follower
"Nitin" wrote in message oups.com... HEllo Guys, I am trying to design a Emitter Follower. I am trying to give the load resistance as 50 Ohm. Could some one tell me how to calculate the Biasing resistance on the Base circuit of the transistor.I am assuming that the Short circuit current gain (Beta = 100). I am using a npn 2n2222a transistor for my purpose. Voltage supply on the collector is 12V. Voltage supplied to the base is from the output of a sound card or a signal generator.So please help me in getting the answers Regards Nitin I'm curious- why a 50 Ohm load? Is this a college homework assignment by any chance? Dave |
#3
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Emitter Follower
"Dave D" wrote in message ... "Nitin" wrote in message oups.com... HEllo Guys, I am trying to design a Emitter Follower. I am trying to give the load resistance as 50 Ohm. Could some one tell me how to calculate the Biasing resistance on the Base circuit of the transistor.I am assuming that the Short circuit current gain (Beta = 100). I am using a npn 2n2222a transistor for my purpose. Voltage supply on the collector is 12V. Voltage supplied to the base is from the output of a sound card or a signal generator.So please help me in getting the answers Regards Nitin I'm curious- why a 50 Ohm load? Is this a college homework assignment by any chance? Dave Try http://hyperphysics.phy-astr.gsu.edu...nic/npncc.html Arfa |
#4
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Emitter Follower
Dave;
I really hope it's not college level, this should be in high school. Common collector amps are the simplest to design. Actually I'm a bit squeaky when it comes to common emitter and especially common base stages' actual input impedance. In general in those stages I use a heavy handed approach, make it damped (shunted) and linear. Anyway, now that you got me on the subject, people have looked at me funny for saying this; All bipolar transistors operate as common emitter. No exceptions. This was in response to the inability of a buddy of mine in trade school to understand the concept. I had to draw it about 15 different ways but he finally got it. I almost went into sign language !, that is I was to the point of holding up three figners and saying sternly "OK, my thumb is the emitter ok ?" I didn't have to resort to that but it was close. It was a success, and he actually doesn't make more money, but he moved from 90 hours a week to 40 hours a week to make about $50,000. Not bad, it's just about a whole dollar every day. To the OP; In common collector (emitter follower) the resistance presented by the base is approximately the load resistance times the current gain of the transistor. This current is applied (V / RL X hfe) in the direction of whatever is biasing the emitter. As long as the collector is solidly connected to the Vcc, and input is reference to a propely bypassed Vcc return this is close enough. When the collector voltage is allowed to vary, like by a resisor, this is not accurate. I am not abject to giving help on school projects, but if it is please say so. For one, this cheap and dirty formula dfoesn't work with anything else. If you don't learn it the right way you will fall flat on your face later. Also, if RL=50 ohms, your wimpy little transistor will have to dissipate at the very least 720 mW even during quiescence. A 2N2222 is going to have a problem with that, you will at least need a heatsink. In fact you might need Freon ! If you're talking about buffing a soundcard output, this is not the way to go. If you simply get an older soundcard that doesn't require powered speakers you are fine. They will feed 50 ohms no problem. A sig generator, OK, mine for example is 30 volt @ 600 ohms output. But then what would stop you from just feeding that to the soundcard ? JURB |
#5
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Emitter Follower
In article .com,
Nitin wrote: I am trying to design a Emitter Follower. I am trying to give the load resistance as 50 Ohm. Could some one tell me how to calculate the Biasing resistance on the Base circuit of the transistor.I am assuming that the Short circuit current gain (Beta = 100). I am using a npn 2n2222a transistor for my purpose. Voltage supply on the collector is 12V. Voltage supplied to the base is from the output of a sound card or a signal generator.So please help me in getting the answers It's not the correct transistor to drive a 50 ohm load. -- *Real men don't waste their hormones growing hair Dave Plowman London SW To e-mail, change noise into sound. |
#6
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Emitter Follower
"Arfa Daily" wrote in message ... "Dave D" wrote in message ... "Nitin" wrote in message oups.com... HEllo Guys, I am trying to design a Emitter Follower. I am trying to give the load resistance as 50 Ohm. Could some one tell me how to calculate the Biasing resistance on the Base circuit of the transistor.I am assuming that the Short circuit current gain (Beta = 100). I am using a npn 2n2222a transistor for my purpose. Voltage supply on the collector is 12V. Voltage supplied to the base is from the output of a sound card or a signal generator.So please help me in getting the answers Regards Nitin I'm curious- why a 50 Ohm load? Is this a college homework assignment by any chance? Dave Try http://hyperphysics.phy-astr.gsu.edu...nic/npncc.html Arfa Erm, thanks- but you're replying to the wrong post ;-) Dave |
#7
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Emitter Follower
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#8
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Emitter Follower
"Dave D" wrote in message ... "Arfa Daily" wrote in message ... "Dave D" wrote in message ... "Nitin" wrote in message oups.com... HEllo Guys, I am trying to design a Emitter Follower. I am trying to give the load resistance as 50 Ohm. Could some one tell me how to calculate the Biasing resistance on the Base circuit of the transistor.I am assuming that the Short circuit current gain (Beta = 100). I am using a npn 2n2222a transistor for my purpose. Voltage supply on the collector is 12V. Voltage supplied to the base is from the output of a sound card or a signal generator.So please help me in getting the answers Regards Nitin I'm curious- why a 50 Ohm load? Is this a college homework assignment by any chance? Dave Try http://hyperphysics.phy-astr.gsu.edu...nic/npncc.html Arfa Erm, thanks- but you're replying to the wrong post ;-) Dave Dave - I was referring the OP to that site, and not replying specifically to your question about the 50 ohm load. The site has information relevant to his query about how to calculate the values of bias resistor for a common collector stage, with BIGGGG simple diagrams ... Sorry if it confused - I was just tacking onto the bottom of the thread for the benefit of those following it, rather than sticking my bit in the middle. Arfa |
#9
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Emitter Follower
"Arfa Daily" wrote in message ... Dave - I was referring the OP to that site, and not replying specifically to your question about the 50 ohm load. The site has information relevant to his query about how to calculate the values of bias resistor for a common collector stage, with BIGGGG simple diagrams ... Sorry if it confused - I was just tacking onto the bottom of the thread for the benefit of those following it, rather than sticking my bit in the middle. Arfa No worries, Arfa, we've all done it! Dave |
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