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common emitter circuitry.

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as you all know i'm still learning. i'm trying to learn now about the common transistor circuits(CC, CB,CE) i'm working with this circuit right now.


with a pn5551 trans. i have a question. which resistors can i change with out blowing the trans?

I have yet to play with the circuit to much because i want to get the kitchen done B4 i get busy with this. but i do have it together with all the same resistors here just a dif trans.

Thanks for any info! _Chris:D
 

AllVol

New Member
The included attachment might be of interest to you, if you will study it.
 

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ljcox

Well-Known Member
mybuickskill6979 said:
as you all know i'm still learning. i'm trying to learn now about the common transistor circuits(CC, CB,CE) i'm working with this circuit right now.


with a pn5551 trans. i have a question. which resistors can i change with out blowing the trans?

I have yet to play with the circuit to much because i want to get the kitchen done B4 i get busy with this. but i do have it together with all the same resistors here just a dif trans.

Thanks for any info! _Chris:D
The site you posted is a good source of info. And the circuits posted by AllVol are also good.

Transistors can be blown by:-
  1. Too much collector current
  2. Too much base current
  3. Too much power dissipation.
So you need to study the data sheet of the transitor in question and look at the maximum limits.

The power dissipation is at a maximum at half voltage and half current.

For example, if you have say a 10 Volt supply connected via a 10k resistor to the collector of an NPN and the emitter connected to gnd, then the max diss is when the collector is at 5 Volt so the collector current is (10 - 5)/10 = 5 mA.

Hence the power diss is P = Vce * Ic = 5 * 5 = 25 mW.

When the transistor is off, Vce = 10 Volt, but Ic = 0 so P = 0

When the transistor is saturated, Vce = 0.1 Volt approx, Ic = 10 ma so P = 0.1 * 10 = 1 mW.
 
awesome. will definitely take this into consideration i'm gonna have the neighbor print the datasheet out( im out of ink lol) and keep it by me while messing with it!!
 

Roff

Well-Known Member
ljcox said:
<snip>And the circuits posted by AllVol are also good.<snip>
No they're not. The configurations are identified correctly, but the transistor in Fig. 4A is nearly saturated, and could be biased for much higher signal swing, and somewhat lower input capacitance (due to higher Vcb). The transistor in Fig. 4B is saturated. The transistor in Fig. 4C is nearly cut off. The transistor in Fig. 7 has collector and emitter swapped (emitter-base junction is used as a zener when connected correctly).
 

AllVol

New Member
Yeah, and your picture looks just like you.


Seriously, don't blame me. I just copied them for reference from one of the tutorials.

Edit: If what you say is correct, then its a sad commentary on some of the supposedly accurate tutorials found on the internet. That particular composite came from a web site of a guy who is pretty prominent on the 'net and pops up in many searches. If he is wrong, then how does a noobie differentiate? Or must we hobbists just chuck the whole thing because what we're being told is false information.

(I think an ear tuck would do wonders for your self-esteem. hehe)
 
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Roff

Well-Known Member
AllVol said:
Yeah, and your picture looks just like you.
Amazing how that works, huh? :D


Seriously, don't blame me. I just copied them for reference from one of the tutorials.
I wasn't blaming you. I was just warning unsuspecting hobbyists.
 

Roff

Well-Known Member
AllVol said:
Yeah, and your picture looks just like you.


Seriously, don't blame me. I just copied them for reference from one of the tutorials.

Edit: If what you say is correct, then its a sad commentary on some of the supposedly accurate tutorials found on the internet. That particular composite came from a web site of a guy who is pretty prominent on the 'net and pops up in many searches. If he is wrong, then how does a noobie differentiate? Or must we hobbists just chuck the whole thing because what we're being told is false information.

(I think an ear tuck would do wonders for your self-esteem. hehe)
I got the common base stage all wrong. With a beta of 100, the collector current is only about 160uA, making the collector voltage about 8.24V. Not sure what I was thinking, as the transistor actually needs more current, not less. I was right about the other two. The graphics look like **broken link removed**, although I didn't find those drawings when I looked for them. There are some good-looking transistor tutorials there, although they may have schematic errors - I didn't check.
 

Sceadwian

Banned
It's a good rule of thumb, though not much used anymore, especially in journalism or in any facet of life to 'check all your facts'

Which leads to my favorite movie quotes of all time.

"Assumption is the mother of all **** ups" from Dark Siege 2

The second most favorite one being.
"I am Invincible" Famous last words from "Boris" in a James Bond movie said just before he's drenched in a few hundred gallons of liquid nitrogen.

"But he said" is often times used as an excuse when all is said and done, and that's just as bad when making assumptions on designs from the Internet as it is from people in an army taking orders from a superior officer when lives are on the line.
 

Roff

Well-Known Member
AllVol said:
Yeah, and your picture looks just like you.

(I think an ear tuck would do wonders for your self-esteem. hehe)
Yeah, I see you just started using a picture of yourself as your avatar. You are one fine-lookin' dude!
Regarding my ears - how are you at Photoshop?
 

AllVol

New Member
Ron H said:
Regarding my ears - how are you at Photoshop?

I haven't sprung for that program... figure I spend too much time at this keyboard as it is. I can do some light photo editing in Microsoft Paint, which is a more powerful program than many realize.

Yeah, those came from one of Tony's tutorials... I didn't want to ID him as such. Surprising... and I thought the transistor used as a zener was right!

But speaking of Photoshop, did you catch the guy in another thread who said he only had Sketchup? I checked it out, and downloaded the free version. Really interesting program designed primarily for the architect or engineer who wants a quick visual of an idea. It renders in perspective, and the image can be rotated, orbited and zoomed among other things. The pro model (read pay for) can do much more, naturally.

Thanks for the comment on my appearance. I try not to use my real image for fear people will recognize me and cause lots of grief. You know how that is.
 

fingaz

Member
Sceadwian said:
It's a good rule of thumb, though not much used anymore, especially in journalism or in any facet of life to 'check all your facts'

Which leads to my favorite movie quotes of all time.

"Assumption is the mother of all **** ups" from Dark Siege 2
QUOTE]

I always believe that if you 'assume' it makes an ASS of U and ME
 

AllVol

New Member
Ron H The graphics look like Tony Van Roon's although I didn't find those drawings when I looked for them .[/quote said:
Well, here they are: **broken link removed**
 
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audioguru

Well-Known Member
Most Helpful Member
The University of Guelph is out in the sticks. They specialize in agriculture and verterinary stuff, not electronics.
 

ljcox

Well-Known Member
Ron H said:
No they're not. The configurations are identified correctly, but the transistor in Fig. 4A is nearly saturated, and could be biased for much higher signal swing, and somewhat lower input capacitance (due to higher Vcb). The transistor in Fig. 4B is saturated. The transistor in Fig. 4C is nearly cut off. The transistor in Fig. 7 has collector and emitter swapped (emitter-base junction is used as a zener when connected correctly).
It looks as though I should have studied them in more detail.
 

Roff

Well-Known Member
ljcox said:
It looks as though I should have studied them in more detail.
Note that I made a later post where pointed out that I was in error about the common base circuit. It could use some redesign, but my initial comments were wrong.
 
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