Kevin Weddle Posted October 21, 2004 Report Share Posted October 21, 2004 I have this weird circuit that I can't devulge too much about. It involves feedback and high current transistors and time delay. What I would like to know is if the beta of a high current transistor can change drastically. If I apply a large signal to the base, I get a large change in current. This large change in current produces a large change in base current. My impedance is reduced by the large change in base current resulting in a reduction of base voltage. Now before you comment, the circuit is already biased, built and tested with many transistors. What I get with feedback and some time delay is a halving of voltage. Does a halving of voltage mean something to anyone and can the beta change enough to lower my impedance so that I get a halving of voltage? Quote Link to comment Share on other sites More sharing options...
ante Posted October 22, 2004 Report Share Posted October 22, 2004 Kevin,Please post the circuit so we can see what you are talking about. Quote Link to comment Share on other sites More sharing options...
surajbarkale Posted October 25, 2004 Report Share Posted October 25, 2004 Weird Description ;D Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted October 26, 2004 Author Report Share Posted October 26, 2004 There is an update to the circuit I posted. It works fine. I am still getting a halving of the signal but I think it is arbitrary. It was not a change in beta that was the problem. It has to do with source of the signal and the feedback which is secondary. You can only create a certain amount of response with the signal source before you negate the whole thing. The resistance was the other part of the problem. I figured I could increase the change in current to get the gain, and it does, but only to the extent dictated by the signal source. So I am left with the feeling that there is something special to the voltage halving. Although I really can't say that it is exactly half. I would like to think it's about half, to be determined by the change in current. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted October 26, 2004 Author Report Share Posted October 26, 2004 There is another update to my circuit. It is amazing that the calculations prove to be correct. The problem I was experiencing was from excessive signal amplitude. You should probably use less than 1Vpp when analyzing your circuit. Quote Link to comment Share on other sites More sharing options...
Kevin Weddle Posted October 26, 2004 Author Report Share Posted October 26, 2004 And one final update. The impedances do win. The calculations even with feedback prove to be true. It was not the signal amplitude. It was a mere fact of impedance. However in my circuit, I am going to allow the feedback signal to produce the same change in base current as the signal source. The impedance and the voltage will allow me to do this. Quote Link to comment Share on other sites More sharing options...
ante Posted October 27, 2004 Report Share Posted October 27, 2004 Yes, this sounds like a very weird circuit! I wish I could see it though. Quote Link to comment Share on other sites More sharing options...
audioguru Posted October 28, 2004 Report Share Posted October 28, 2004 However in my circuit, I am going to allow the feedback signal to produce the same change in base current as the signal source. The impedance and the voltage will allow me to do this. Huh? That's weird.How can the feedback produce the same change in base current as the signal source, unless it is positive feedback?I've always thought that negative feedback cancels some of the input, therefore reducing gain.Where's the circuit that "you posted"? Quote Link to comment Share on other sites More sharing options...
ante Posted October 30, 2004 Report Share Posted October 30, 2004 Is it just me, or Quote Link to comment Share on other sites More sharing options...
MP Posted October 30, 2004 Report Share Posted October 30, 2004 Kevin, please post the circuit. I think you are having fun with a riddle?MP Quote Link to comment Share on other sites More sharing options...
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