[Al_The_Man]

The bottom line is that if base current flows, wether PNP or NPN the transistor would turn on. Base current in either causes emitter-collector current to flow.
They are both switches and both turn on when current is applied.
I believe the confusion is arising because you may be looking from the voltage level perspective and not current.
The PNP does NOT stop conducting when base current appplied.
If you want an analogy to turning on a tap, imagine two taps side by side but one you turn CW for flow, the other CCW for flow, both can confuse.
Al.

[fkaCarel]

PNP and NPN are mirrored devices. You apply current to an NPN make it conduct. Base voltage higher then emitter. You draw current from an PNP. Base voltage lower than collector.

Carel

[Al_The_Man]

PNP and NPN are mirrored devices. You apply current to an NPN make it conduct. Base voltage higher then emitter. You draw current from an PNP. Base voltage lower than collector.

Carel

But wether the current is 'in' or 'out' of the base, current still flows for turn on in each.
As I pointed out, the voltage term should not be used in bipolar transistors because they are current devices.
The confusion can arise when the action is viewed from the voltage perspective.
Al.

[martinw]

060517-1846 EST USA

Libraries or your own books are the best way to do this.
.

The very best book ever written is The Art of Electronics by Horowitz and Hill.

You do not need a degree in electronics to benefit from it. It is refreshingly light on maths, brilliantly written, and enormous fun. I would urge anybody to get a copy. ( No, I am not on commission!)

Martin

[lwill]

Not to be more confusing, but in a sence you are all three right. the poarity of the voltage will determin current flow therefore applying a positive voltage (relative to emmiter) to base of NPN causes current to flow from base to emmiter and a larger current from colletor to emitter, PNP is the other way around, negative voltage to base (reletive to emmiter) causes current from emmiter to base and larger from emmiter to collector. it is all relitive to the refferance point you look at. Also depends if you are talking conventional current flow or electron flow (learnd one way and was latter taught the other so always get them confused) so in a sence if you change your point of refferance then it will appear to be turning "off" a common error. In my mind I don't care as long as you under stand which gives you the expected result you want. I still think of an NPN as an inverter, apply a 1 and get a 0 (turn it on, and is comes close to a short to ground) even though it is "ON" it looks "OFF" in relitive tearms. PNP is the same way if you measure relitive to possitive. this inconsistance is can be confusing, but if you mind works the way that mine does it makes more sence in everyday use and only have to think about it when questions like this come up. But to a true engineer it annoys the heck out of them!
NC, it is like when I talk to my gear head freinds about cars. I tend to transpose tearms fefering to manual and automatic trans (clutch and toruqe convertor, etc) or carb and FI and it drives them nuts!
ie. does "apply the clutch" mean to make it engage and move, or pressing (appling) the pedel to make it disengage? Depends on your point of refferance.
Back to electronics, just don't ever talk to an EE about voltage "flowing", thier head will elplode!

[gar]

060519-1001

As has been pointed out a bipolar transistor is a three terminal current controlled device. This has essentially two diode junctions constructed together is such a way that that current flow in one junction modulates current in the other junction. One junction is forward biased and the other is reversed biased.

The sum of the currents at any point is zero. Consider a simple wire and pick any point on that wire. Assume the current flowing to the point from one side is positive, then the current flowing to that point from the opposite side is negative, and therefore the sum is 0.

Now consider the three terminal transistor. The normal transistor mode is the base to emitter junction is forward biased, and the collector to base diode is reverse biased. It takes only a small base current to produce a large change in collector current. The beta of a transistor is the ratio of collector current change to base current change. For a junction transistor current gain from emitter to collector is always just slightly less than 1 and is a function of beta.

With zero current to the base there is a small current flow from collector to emitter. This is called the collector leakage current, and it is temperature dependent and grows with increasing temperatrure. This is similar to the reverse leakage current of a diode.

Notice I have said nothing about NPN or PNP.

The difference is that for transistor action an NPN will have its emitter more negative than base and collector. Positive current to the NPN base causes positive current flow to the collector to increase. Thus, the sum of the positive base and positive collector currents flowing into the transistor equals the positive current flowing out of the emitter, or the negative current flowing into the emitter. For a large beta notice that collector current almost equals emitter current.

For an PNP just change my positives to negatives. Otherwise the operation is the same. The difference is only a matter of the direction of current flow.

Since the base to emitter junction looks like a diode it has the same kind of forward biased nonlinear voltage current curve. A small forward bias voltage change at the base relative to emitter produces a large current change in the collector circuit.

Some more on educational philosophy.

The original question was:

"I take a 7406 Inverter chip (SL74LS06), no resistors and a 5VDC power source.

With the chips Vcc connected to 5VDC and the GND connected to GND, why does 5VDC on an input pin not give a LOW voltage on the corresponding output pin and why does 0VDC on an input pin not give a HIGH voltage on the corresponding output pin?

Should I be concerned about amperage or using pull-up or pull-down resistors?"

Later RotorRouter said he had spent a very great amount of time to studied the data sheet and did not understand the data sheet. This should have been part of the question.

Also should have been asked if the 7406 was the best solution for the application. Further, if the load was to be an electromagnetic relay, then there are problems related to the inductive kick on turn off. If the load was another TTL gate, then maybe a TTL output would be better. If only one channel was needed, then maybe a 2N7000 would be a good choice.

First, a 7406 with Vcc applied, and a +5 signal on the input does give an essentially 0 V output and also a moderately low output impedance to common in contrast to what was stated in the question. The second part of that question sentence is OK.

The TI data sheet clearly states in words that the output is an open collector device at the very top of the sheet. Then later in the data sheet a circuit diagram shows the output as an open collector.

My criticism here is not particularly with RotorRouter but with what I see prevalent in interent forums of questioners not having a basic understanding of the subject area with which they are playing. And their interest in the answer is to a very limited question without wanting to know the fundamentals so that in the future they can answer their own question. This goes beyond the internet.

I think that RotorRouter lacks an understanding of transistors, basic electrical theory, what TTL is, or RTL, etc. This is where basic understanding is important and it is best obtained from books where the author has spent a lot of time researching the subject and how to present the material clearly. Random responses from people on the internet do not necessarily produce correct answers, and usually not the theory behind the subject.

Ohms law, power dissipation, conservation of energy, temperature rise, thermal resistance, heat transfer, friction, the meaning of ratings, absolute ratings, sum of the voltages around a loop, sum of currents at a point, Norton's equivalent circuit, Thevenin's equivalent circuit, RMS vs peak or average, and waveform, logic equations, Boolean algebra, number theory, magnetic fields, electric fields, etc. are many of the basics that you need for an understanding of electrical products.

A number of years ago I was called to do a service call on a pinion shim machine that was producing erratic results. This was a unionized plant and I got along fine with the workers. But it meant I had to have two machine repairmen, an electrican, and pipefitter to help. It became apparent the problem was mechanical so the electrican and pipefitter disappeared. The machine repairmen did the repair under direction but were unwilling to understand the cause, and thus prepare themselves to solve a similar problem in the future on their own. Had these been some Japanese visitors they would have been all over the machine trying to figure out how it worked in every detail.

.

[lwill]

Another point of confusion, more to the point of the original post. When I first started working with logic gates I tended to think of them in terms of reverse logic. That is, since I was dealing with gates that were internaly pulled high on input and output, apllying power (logic 1) to a pin didn't have any effect on the output but apllying ground (0) did. Sitting with no connection, the pins think they are high already which was contrary to simple thinking. In tearms of a switch like a NO push button it is off untill you press it, but a gate with a internal pull up on an input is already on untill you turn it off, to my way of thinking "if I didn't hook anything to it, it must be off, right?" The oppisit is true on the output, measuring a OC output with a meter to ground (with no pull up connected) shows no change in output, but measure it relitive to possitive and "Vala!" it seems to work.
My main point is, in everyday use (for non-engineers) figure out how it works in your own terms that make sence to you and stay consistant and you will be ok. Just beware of talking to others in your terms with out knowing the proper ones, you may get some strange looks.

[lwill]

I saw a excelent speaker on PBS once (Loel Caddet? Cattlet?) who said in the futer the answers will be easy, we will have calculators and the internet on our wrist. The problem is asking the right question! Does memerising multiplecation tables make us smarter? If it teaches you "how to learn" then yes, ohter wise remembering the answer does no good if you can't solve a problem since you don't know the question to begin with. Teach critical thinking and problem solving, don't teach answers.
On the other hand, this is not a school, it is a forum to get questions answered, and knowled horded is knowledge wasted. Albert E. found more questions than answers and where would we be if kept what he learned to himself and didn't share?

[RotorRouter]

NC Cams

Your position has strong validity, particularly for those who have the need or the desire, plus the time, to delve deeply into a subject. For me, the building of a CNC controller is interesting, but it is also a means to an end.

I know little about electronics and therefore expiditiously seek specific information from books, Google and knowledgeable people.

Conversely;

I have acquired some technical knowledge about rotorcraft. It is freely offered on the Internet by a web site with over 1,000 pages[UniCopter], and by two-way communication on related rotorcraft Forums. This web site has been a lot of work, but over the years it has been a wonderful way to provide and acquire information.

Want to build a helicopter?

Dave

[NC Cams]

RotorRouter: You have to read deeper into my replies as I'm trying to comply with the policy of this m/b as in, "...resist the urge to curse, flame, degrade, insult or embarrass someone in your post...." I find it hard sometimes to comply with this request.

I find it VERY hard to comprehend how people will get involved with a project that REQUIRES the utilization of basic electical engineering principles and NOT take the time to learn them.

Yet, they'l mess with stuff before they even tried to learn even the basics as clearly apparent by many questions. Ignorance is associated with a person who has a lack of knowledge. Stupidity is reserved for someone unwilling to try to learn. Big difference.

In today's world, it is NOT hard to find the answers to darn near anything, especially if you have access to Google, Ask.com, etc and are willing to do even a BIT of research.

For example, if you're going to try to conjure up your own power supply, doesn't it seem even slightly reasonable to expect folks to do a bit of reasearch into the how's and why's? Especially if/when you're going to work with electrical power that could KILL you???.

Anyway, from this M/B, I learned of

http://www.cnczone.com/forums/showth...015#post142015

http://forums.bit-tech.net/showthread.php?t=108208

http://www.campbelldesigns.com/files...ply-part-1.pdf

all of which can be found without a lot of effort

Similarly, we have the perenial "what wire do I use" question:

Answer:
http://www.cnczone.com/forums/showthread.php?t=17350

http://www.cnczone.com/forums/showth...480#post136480

Don't forget the repeatedly asked "stepper vs servo" question:

http://www.cnczone.com/forums/showthread.php?t=17419


If you'r going to retrofit a Bridgeport, wouldn't a simple "CNC retrofit" or "CNC retrofit bridgeport" google search be a starter???

The prior sentence is how I found this website and have been a participant/contributor since.

However, like GAR says, at some point BASIC electronics knowledge is ESSENTIAL, no MANDATORY when it comes to DIY CNC.

How did I learn??? Earth science in high school (35 years ago) and lots of reading of Popular Electrnics and many model train electronics books and/or Radio Shack books since then.

The Popular Electonics mags and model train books from Kalmbach Publishing will get ANYBODY enough DC circuit knowledge to go from being ignorant to reasonably informed - and asside from the power levels, will give nearly anybody the fundamentals to DC motor control.

Too bad model trains aren't as popular as computers anymore - Learned a lot about wiring from my Lionel days....

Once you get to a point of "model train knowledge", some of the Forrest Mims books will further enlighten even mechanical engineers (his presentation was something even I could understand).

To which I must contribute the following:

http://www.forrestmims.com

http://www.amazon.com/gp/product/pro...lance&n=283155

The neophyte DIY CNC'er should buy some of Mims books.

Add a dab of understanding of Ohms laws (E=IR) and power equations (P= I*I*R) and a lot of the redundantly asked questions get answered and knowledge, not answers, get passed on.

A link to the source found in Post #24 above if found below:

http://www.amazon.com/gp/product/052...lance&n=283155

http://www.amazon.co.uk/exec/obidos/...924843-3042007

I've ordered from UK and shipment to USA takes about a week.

Currently, I'm not in the market to get involved with helicopters. But rest assured, the day I do, I'll be hunting down your site and any others.

Why? To learn the lingo BEFORE I go to your or anybody's website and ask even the most elementary of questions.

I am currently ignorant of moveable wing aircraft but if I get interested in them, I won't allow myself to be perceived as being stupid.

I too don't have the time to learn electronics to the level of GAR. However, due to a lack of funds, I've had to learn how to fix, connect and maintain my shop equipment which has allowed me to learn a lot about stuff I NEVER planned to learn about.

This includes 20+ year old Fanucs (TTL circuits are real insensitive to ground currents), 12 year old Bridgeport ExTrak (numberous posts about which are on this website) and a like new but designed in the 60's Berco cam grinder (Italian made and DON'T get me started on Italian logic).

My problem solving training as an engineer is what enables me to self service equipment that isn't supported anymore or I can't afford to pay somebody to come in and pay to fix. Dare I say the many of the DIY'er CNC guys are doing the same thing for the EXACT same (financial reasons).

Since I walk in their shoes, I will close by urging/encourabing those who are interested in building their own CNC to learn the basics - links are provided above. Move away from ignorance and don't allow yourself to become stupid.

The basic knowledge is helpful, no ESSENTIAL to understanding and trouble shooting DIY CNC equipment. This is something that WILL inevitabley have to be done sooner or later...

If man made it, sooner or later, it will malfunction.