Discrete opamp bjt front end

[Eeyore]

Here it is winter with summer temperatures,

It's very mild here too.

I just went out in jeans and T-shirt.

Graham

 

[Jim Thompson]

martin griffith wrote:
Ok, this is a classic audio doofer
http://johnhardyco.com/pdf/990.pdf

[snip]

What a piece-a-crap.

I've got to get into this audiophool business... looks like all kinds
of dummies sitting there ready for the taking ;-)

...Jim Thompson

Talking shit about politics does not qualify you for talking shit about
electronics.

DNA

I thought I had already earned the second ?

...Jim Thompson

 

[Genome]

[snip]

What a piece-a-crap.

I've got to get into this audiophool business... looks like all kinds
of dummies sitting there ready for the taking ;-)

...Jim Thompson

Talking shit about politics does not qualify you for talking shit about
electronics.

DNA

 

[Genome]

"Fred Bartoli"

martin griffith a écrit :


One clicked at random from all the list...

http://pag.csail.mit.edu/~adonovan/dilbert/show.php?day=6&month=2&year=1999

What are the chances of that!!!!!!!!????????

Sales Rep.....

Has to roll up his shirt sleeve to take a shit.

DNA

 

[Genome]

martin griffith wrote:
Ok, this is a classic audio doofer
http://johnhardyco.com/pdf/990.pdf
[snip]

What a piece-a-crap.

I've got to get into this audiophool business... looks like all kinds
of dummies sitting there ready for the taking ;-)

...Jim Thompson

Talking shit about politics does not qualify you for talking shit about
electronics.

DNA

I thought I had already earned the second ?

...Jim Thompson
--

Oh, alright then.

Talking shit about electronics does not qualify you for talking shit about
politics.

However, it seems you might be confusing the issues with rights. Try to stay
on subject.

DNA

 

[Ban]

Actually there is.

Graham

That's interesting, where is it?

 

[Jim Thompson]

"Fred Bartoli"


What are the chances of that!!!!!!!!????????

Sales Rep.....

Has to roll up his shirt sleeve to take a shit.

DNA

So he's a _normal_ sales rep ?

...Jim Thompson

 

[Eeyore]

That's interesting, where is it?

CR11,12. If the output current x Remitter exceeds the diode forward voltage, it
clamps the drive. It's not very intuitive though.

Graham

 

[Ban]

CR11,12. If the output current x Remitter exceeds the diode forward
voltage, it clamps the drive. It's not very intuitive though.

Graham

Nope. Bad shot, Graham.
These diodes are there to pull up the base in case of inductive kickback
current. This is better than putting them to the rails, because then the
transistor breaks down with negative Vbe.
If they were for current limiting, they had to be turned around and
doubled(or a red LED) to allow also for the Vbe of the transistor.

 

[Fred Bartoli]

Ban a écrit :

Nope. Bad shot, Graham.
These diodes are there to pull up the base in case of inductive kickback
current. This is better than putting them to the rails, because then the
transistor breaks down with negative Vbe.
If they were for current limiting, they had to be turned around and
doubled(or a red LED) to allow also for the Vbe of the transistor.

Didn't say anything 'cause I waited to see.
The thing is, there's still current limitation.

Think harder

 

[Robert Latest]

On Thu, 30 Nov 2006 08:22:14 +0100,
Fred Bartoli wrote

Didn't say anything 'cause I waited to see.
The thing is, there's still current limitation.

Imax = Ub/3.9. That's a limit.

Actually it's four diode drops / 3.9 Ohms, that's .7 A.

robert

 

[Fred Bartoli]

Robert Latest a écrit :

On Thu, 30 Nov 2006 08:22:14 +0100,
Fred Bartoli wrote


Imax = Ub/3.9. That's a limit.

Actually it's four diode drops / 3.9 Ohms, that's .7 A.

Actually it's not four diode drops.

 

[Eeyore]

Nope. Bad shot, Graham.
These diodes are there to pull up the base in case of inductive kickback
current. This is better than putting them to the rails, because then the
transistor breaks down with negative Vbe.
If they were for current limiting, they had to be turned around and
doubled(or a red LED) to allow also for the Vbe of the transistor.

It told you it wasn't intuitive.

It limts the base-base voltage to 3 diode drops.

Look at it again.

Graham

 

[Eeyore]

On Thu, 30 Nov 2006 08:22:14 +0100,
Fred Bartoli wrote


Imax = Ub/3.9. That's a limit.

Actually it's four diode drops / 3.9 Ohms, that's .7 A.

Four ? I make it 3. And you forgot to take away the Vbe.

Graham

 

[Robert Latest]

On Thu, 30 Nov 2006 09:36:54 +0100,
Fred Bartoli wrote

Robert Latest a écrit :

Actually it's not four diode drops.

Right. Vbe counts in the other direction, so it's two drops.

robert

 

[Eeyore]

On Thu, 30 Nov 2006 09:36:54 +0100,
Fred Bartoli wrote


Right. Vbe counts in the other direction, so it's two drops.

~ 2 x Vf / Remitter is indeed the current limit.

It's more obvious if you redraw the circuit.

Graham

 

[Ban]

~ 2 x Vf / Remitter is indeed the current limit.

It's more obvious if you redraw the circuit.

Graham

Then how long will it survive an accidental short O/P to V+/- ? That
makes 46.5V *.38A =17.88W dissipation in one transistor. Good luck.

 

[Eeyore]

Then how long will it survive an accidental short O/P to V+/- ? That
makes 46.5V *.38A =17.88W dissipation in one transistor. Good luck.

In its intended application that simply won't happen. Why would it short to
supply anyway ?

Graham

 

[Jan Panteltje]

Then how long will it survive an accidental short O/P to V+/- ? That
makes 46.5V *.38A =17.88W dissipation in one transistor. Good luck.

Is the current not also limited by beta x the current drive?

The drive current (bottom transistor) is 0.7 / 110 = 0.6mA.
The beta of the MJE-171 is perhaps about 50, so the I max is 30mA.
At half supply 24V makes .03 x 24 = 720mW in the pulldown.
Pullup will be about the same.

Grin

 

[Jan Panteltje]

Is the current not also limited by beta x the current drive?

The drive current (bottom transistor) is 0.7 / 110 = 0.6mA.

Correction, math, 0.7 / 110 = 6.3 mA

The beta of the MJE-171 is perhaps about 50, so the I max is 30mA.

now 300.
oops.