2N3055 barrier height potential

[Tim Wescott]

Well, he did reinforce the point that simulation sometimes produces
wildly unrealistic results. People need to get out of their chairs,
get vertical, and measure a real part once in a while. Seems like some
goodly fraction of the youngsters playing with this stuff these
believe that electronics *is* simulation. I'm told that many college
EE "lab" courses just simulate.

John

My very favorite undergrad professor of all time retired about five
years after I graduated when my alma mater went to all-simulation in the
EE labs. It's a pity -- building op-amps from transistor arrays on
those crappy little white proto boards really teaches you about
bypassing and the difference between a line on a schematic and a real
(or really bad) conductor.

Conversation between Tim the Teaching Assistant and a fraternity kiddie
in the 4th-year analog circuits lab:

Kiddie: "There's something wrong with this circuit, the voltage is all
wrong"

Tim: "Have you looked at it with a scope?"

Kiddie: "Scope? I'm putting DC in"

Tim: "Look at it with a scope"

(Kiddie reluctantly acquiesces): "Hey! It's outputting this weird
square-wave thingy".

Tim: "Check your circuit, I'll come back"

(5 minutes later)
Kiddie: "It all matches, my transistor arrays must be bad"

Tim: "Why don't you try bypass caps?"

Kiddie: "Bypass caps?"

(note: professors at WPI don't teach about bypass caps, seem unaware of
their existence. They also don't teach about polarity of electrolytics,
but that's another story...)

(Argument ensues about necessity of bypassing a 5-chip circuit on a
protoboard hanging on 5-foot power cables, ends with...)

Tim: "I can't help you until you put in bypass caps. If you come to me
again and I don't see bypass caps I'll just tell you to put them in.
Put in 0.1uF caps here and here, and come get me when you're done"

(Tim ignores that part of the room for 10 minutes, comes back)

Tim: "How's it going?"

Kiddie, in bafflement: "It all works now, but why did putting in these
useless capacitors make a difference?"

 

[colin]

I think it's down to me, I suspect. I really shouldn't have continued
to use that same circuit fragment in an attempt to investigate Vbe.
It's better achieved with the current source technique Genome posted
elsewhere.

*blows of dust from big box of 2n3055's and puts fluke 77 acros them*

lowest i got was 430 mv highest just over 500mv seems 2n3055A (hepetaxial or
someithing i think the diference is) have a lot lower vbe than standard
2n3055 (actualy i fnd one a lot lot lower but decided to throw it out)..

vbe changes 60mv per dacade of curent. 350mv sounds way to low for any
reasonable curent.

COlin =^.^=

 

[John Larkin]

My very favorite undergrad professor of all time retired about five
years after I graduated when my alma mater went to all-simulation in the
EE labs. It's a pity -- building op-amps from transistor arrays on
those crappy little white proto boards really teaches you about
bypassing and the difference between a line on a schematic and a real
(or really bad) conductor.

Conversation between Tim the Teaching Assistant and a fraternity kiddie
in the 4th-year analog circuits lab:

Kiddie: "There's something wrong with this circuit, the voltage is all
wrong"

Tim: "Have you looked at it with a scope?"

Kiddie: "Scope? I'm putting DC in"

Tim: "Look at it with a scope"

(Kiddie reluctantly acquiesces): "Hey! It's outputting this weird
square-wave thingy".

Tim: "Check your circuit, I'll come back"

(5 minutes later)
Kiddie: "It all matches, my transistor arrays must be bad"

Tim: "Why don't you try bypass caps?"

Kiddie: "Bypass caps?"

(note: professors at WPI don't teach about bypass caps, seem unaware of
their existence. They also don't teach about polarity of electrolytics,
but that's another story...)

(Argument ensues about necessity of bypassing a 5-chip circuit on a
protoboard hanging on 5-foot power cables, ends with...)

Tim: "I can't help you until you put in bypass caps. If you come to me
again and I don't see bypass caps I'll just tell you to put them in.
Put in 0.1uF caps here and here, and come get me when you're done"

(Tim ignores that part of the room for 10 minutes, comes back)

Tim: "How's it going?"

Kiddie, in bafflement: "It all works now, but why did putting in these
useless capacitors make a difference?"

Yeah, Spice has those cool zero-impedance supplies, beta=100.00
transistors, 1 pH inductors, zero-dissipation resistors, and lots of
other stuff you won't find in the Digikey catalog.

John

 

[Paul Burridge]

Bloggs! Get back in your kennel at once, Bloggs!!!

Well, he did reinforce the point that simulation sometimes produces
wildly unrealistic results. People need to get out of their chairs,
get vertical, and measure a real part once in a while. Seems like some
goodly fraction of the youngsters playing with this stuff these
believe that electronics *is* simulation. I'm told that many college
EE "lab" courses just simulate.

I'd have happily measured the part, John, but I must be the only
electronics expert in the UK without one to hand.
Seriously, I used to have a bucket full of 'em from a bunch of old
power supplies, but they were too big and bulky to store tidily.
But you're on to something with the simulation business. I find it's
more fun than building stuff for real. It's certainly a heck of a lot
*quicker* and far less hassle than making boards, trimming components
and sodering them in place by hand. It is virtually an end in itself
for some people, from what I read elsewhere!

 

[Kevin Aylward]

I used a real 2N3055 and a voltmeter. Only beginners need to simulate
stuff this simple.

Add make sure your not using the stock PSpice model. It has a 10 ohm
rbb, resulting in 10V when you feed 1A into the base!!!

Kevin Aylward
[email protected]
http://www.anasoft.co.uk
SuperSpice, a very affordable Mixed-Mode
Windows Simulator with Schematic Capture,
Waveform Display, FFT's and Filter Design.

 

[J M Noeding]

Yeah, Spice has those cool zero-impedance supplies, beta=100.00
transistors, 1 pH inductors, zero-dissipation resistors, and lots of
other stuff you won't find in the Digikey catalog.

John

Indeed, it seem to be based on the theory we already had 35 years ago

-JM