Timeline for Confusion with current in voltage-out amplifier
Current License: CC BY-SA 3.0
29 events
| when toggle format | what | by | license | comment | |
|---|---|---|---|---|---|
| Feb 3, 2016 at 1:02 | vote | accept | user16307 | ||
| Jan 22, 2016 at 14:07 | comment | added | LvW | @Andy aka-ohh no, it was my reply to user`s16307 question "do you use them when designing transistor circuits"? You can trust me, I am aware of your technical competence. Sorry, I forgot to write down to whom it was concerning (linguistic OK?). | |
| Jan 22, 2016 at 13:53 | comment | added | Andy aka | @LvW is your comment starting "of course" aimed at anyone? It sounds like you are informing me!! | |
| Jan 22, 2016 at 13:37 | comment | added | LvW | SPICE is a very versatile tool to demonstrate that a designed circuit works as desired, but it should not be used for designiung the circuit. This would be nothing else than a trial-and-error game with questionable results. | |
| Jan 22, 2016 at 13:34 | comment | added | user16307 | ok i was thinking you design emprically with SPICE simulators in 2016. | |
| Jan 22, 2016 at 13:30 | comment | added | LvW | Of course, we all use h parameters (for low frequency applications) and y-parameters (conductances) for high-frequency circuits. But you should know that different symbols are in use: hfe=beta (current gain), hie=r,pi (base-emitter dynamic resistance). Both parameters are needed for designing an amplifier stage (with DC bias resistors) and for calculating the voltage gain. | |
| Jan 22, 2016 at 13:14 | history | edited | Andy aka | CC BY-SA 3.0 |
added 893 characters in body
|
| Jan 22, 2016 at 13:08 | comment | added | Andy aka | Yeah I know what h parameters are LOL!!! Do I use 'em - not much - every now and then I look at what the hFE is to make sure I can drive a transistor into saturation correctly. | |
| Jan 22, 2016 at 13:06 | comment | added | user16307 | many textbooks use equivalent circuit of transistors and sometimes they use things like h parameters(heard also g but now i dont remember where). they model the transistor to make analysis easy with current sources diodes ect. you know what i mean for sure. im just wondering do you use them when designing transistor circuits or they teach them just to explain the concepts like input output impedance? | |
| Jan 22, 2016 at 12:58 | comment | added | Andy aka | What are "h g parameters"? Nothing is perfect i.e. a perfect voltage-in-amplifier still takes a bit of input-current but, for a specific voltage-amplifier, it's the volts on the input that drives the volts on the output and, any current the input might take (or any current taken by the load), is incidental to the main aim and that main aim, in this example, in this comment, is a voltage amplifier. The BJT is largely regarded as a current-out device but that falls down when the collector voltage is low and it's almost as if the output is a variable resistor. | |
| Jan 22, 2016 at 12:58 | comment | added | rdtsc | This edit and the transistor and the Shockley Diode Equation chart are what @user16307 is looking for and answers why the base behaves as a current input. +1. | |
| Jan 22, 2016 at 12:53 | comment | added | user16307 | by the way do you guys use h g parameters and such theory when designing circuits with transistors? | |
| Jan 22, 2016 at 12:38 | comment | added | user16307 | @LvW my confusion is when I look at for example a 3 stage audio amplifier there are transistors in cascade. and voltage amplifying transistors are NPN or PNP. By looking at the input and output of these transistors is it possible to say if they are current in voltage out or voltage in voltage out or current in current out. just by looking at the circuit can we say that. how? because always some current in and some current out.. and some voltage in and some voltage out as well.. at the same time | |
| Jan 22, 2016 at 12:35 | comment | added | LvW | @user16307, since you are asking for a device "current-in, voltage-out": There is one IC called "NORTON amplifier" with two low-resistive current inputs. But - as mentioned - you can use a voltage-in device (opamp) with feedback as a current-in amplifier (better: I-V converter). | |
| Jan 22, 2016 at 12:29 | comment | added | LvW | I was referring to your diagram (Andy aka) and the replies from user 16307. | |
| Jan 22, 2016 at 12:27 | comment | added | Andy aka | Which answer and which picture and which replies? | |
| Jan 22, 2016 at 12:25 | comment | added | LvW | OK - I was referring to the picture in the first answer - and your replies. | |
| Jan 22, 2016 at 12:17 | history | edited | Andy aka | CC BY-SA 3.0 |
added 1069 characters in body
|
| Jan 22, 2016 at 12:16 | comment | added | user16307 | im not asking about opamps | |
| Jan 22, 2016 at 12:13 | comment | added | user16307 | made an edit to the question | |
| Jan 22, 2016 at 12:12 | comment | added | LvW | @user16307, regarding opamp applications as a TIA: You strictly must discrimnate between the stand-alone unit called "opamp" and an application with external feedback which can be a "current-in" device. The terms "in" and "out" refer to the quantities which are (a) the controlling and (b) the controlled quantities. | |
| Jan 22, 2016 at 12:09 | comment | added | Andy aka | You can make a single BJT TIA of sorts by using collector-base feedback resistors but, because the open-loop circuit gain of a single transistor is rock-bottom compared to an op-amp, it doesn't make a very good TIA. | |
| Jan 22, 2016 at 12:06 | comment | added | user16307 | yes but when you consider its model i mean. different than single transistor amplifier. i mean are you saying with single transistor BJT CE amplifier we cannot say it is current in or voltage in? | |
| Jan 22, 2016 at 12:05 | comment | added | Andy aka | An op-amp is a type of transistor amplifier and you could build a TIA from discrete BJTs if you wanted but who would LOL? | |
| Jan 22, 2016 at 12:04 | comment | added | user16307 | do you mean this terminology makes sense with opamps rather than transistor amplifiers? | |
| Jan 22, 2016 at 12:01 | comment | added | Andy aka | A BJT (getting down to the nitty gritty in the physics) is ultimately a voltage input device but current also flows because of the base-emitter region is a forward biased diode. An op-amp is a bunch of BJTs with negative feedback (Rf) so, in a way there kind of is a BJT equivalent. | |
| Jan 22, 2016 at 12:00 | history | edited | Andy aka | CC BY-SA 3.0 |
added 149 characters in body
|
| Jan 22, 2016 at 11:59 | comment | added | user16307 | is there a transistor equivalent of this? Let me expound on my confusion here. Consider a BJT common emitter amplifier. What if I know both input current and voltage? Will it be voltage in or current in??? | |
| Jan 22, 2016 at 11:57 | history | answered | Andy aka | CC BY-SA 3.0 |