Bnch of transistors trying to wire them up now
whiteoxe
Posts: 794
Is there an east way to tell by looking at thre transistor with the flat area facing you laying on the table , which is the emitter, the one on the right hand side ?
Comments
In the olden days I would look it up in a big book. These days, I get on Google, type the part number (eg BC547) and click on Images.
Also, if you add the word PDF to the search it can find a spec sheet.
I like to use this online resource as well :
http://nte01.nteinc.com/nte\NTExRefSemiProd.nsf/$all/AB409E070C58A7B9852579A30083D4B5?OpenDocument
-Phil
double-check with the transistor tester on your multimeter if it has one or the diode-testing mode if not. That also catches most
duds
Easiest way is to test with the meter on diode range, that way you can confirm which is the base and whether it's NPN or PNP obviously, and by observing the diode voltage drop you can pick out which one is the emitter and collector as the collector reads ever so slightly less.
However most small signal transistors are like this:
..B
E..C
=== FLAT
(BOTTOM VIEW)
The heavier duty TO92s will use the center pin for the collector though as that is simply the way it's constructed with the silicon bonded to the internal metal tab that becomes the middle pin.
I think you meant, "top view."
-Phil
Have fun!
Interesting link Erco, Ill try part numbers though. And my multi meter was a bargain, like 20 bucks, I even used it in the ceiling of my brothers house when running new wires everywhere, just had to know which wire was positve or ground. But other than that i don't know what to use it for or how other and voltage and ohms, its also got amps selector so I really need to begin using that. Here a pic, my close ups are still poor i really need to read the direction manual! THe 5+ Megabytes is ridiculous for this photo, I can set it to take kilobytes but Ill experiment to see how they enlarge ? .
Sounds good ,Feels good
There is no where to plug in components, it will test capacitors which Ive only just noted . But its good for the price around 20 dollars and I really like the automatic ranging when testing resistors. I once had a $10 multimeter but it was a pain to use.
and PS. I bought a cheap pair of 4+ magnifed reading glasses so i didnt have to always use that little monacle type magnifier., even soldering its useful but the +2 glasses seem to keep me away from the fumes better when its over hot, the iron. Im saving up my 1 dollar coins to buy a better iron. Ive seen my 60 watt iron, or one just like it on ebay for $3 no postage. no wonder its junk. I just hope its insulated properly
try 2sc337
Its an NPN C337
and this is my crude way using a simulator to see it work by lighting up a LED by applying voltage to the base.
I coulnt find a microcontroller symbol so this will have to do. There is a lot more current flowing to the base than needs be but it didn't blow up so its an OK start at simulating I think !
The next step is actually using a breadboard until it works !
edit:current ....voltage one of them , volts is what i meant to say.
@Phil, IC's are normally shown top view but transistors traditionally are shown bottom view.
-Phil
That is an interesting circuit to play with. It's not what you want to light up the LED but educational.
My guess was that those 1K resistors are trying to set the base to 3v. Given the voltage drop base to emitter and the voltage required to push current through a LED no base current can flow into the base, the transistor is not switched on and the LED won't light.
We could crank up the supply voltage. Eventually the base is lifted above those voltage drops I mentioned and current runs through it through the emitter and LED. But now we are turning the transistor on quite hard and a lot of current falls down through the collector due to the current gain of the trany. Poof the LED explodes. Well, except you have that 200 ohms to limit that emergency a bit.
A quick simulation shows this is so. Somewhere above 6v supply the LED current runs away. See attached plot from LTSpice.
Notice the voltage across the LED (green) flattens out around 3.8v. This varies with LED colour. Notice how the LED current shoots up out of control around that voltage level.
Notice here transistors are tipped on their side to show the bottom view just like they did with the old tubes/valves which preceded them. This pic has the base inline but on many others the base is bent away as in my diagram:
..B
E..C
=== FLAT
(BOTTOM VIEW)
So bending the base back in it is still correct. Yes/No?
EBC
=== FLAT
(BOTTOM VIEW)
In a grounded emitter the voltage divider only works as such when the input voltage is less than 0.6V but since is 1:1 so half Vin it only needs 1.2V in before it will turn on and clamp and then practically all the current will flow through the base emitter. In Mike's emitter follower circuit I would say that the voltage divider is low enough in resistance to not be affected too much by the combined Rbe*Hfe so it should hold close to 3V while the LED will see 2.6V except it will clamp (within it's limits of course) close to 1.8V for a red LED with >10ma. So yes, Mike's circuit is all wrong for this type of thing.
@Heater, I'm puzzled by the traces, do you have the correct values there? Can you post the schematic as well?
BTW, I'm expecting the LED to exhibit real resistance just like Rbe does too, maybe the sim doesn't take that into account.
But there something very interesting going on with the collector voltage in there:
In my experience, that's an unusual pinout. This is much more common:
Every TO92 BJT I've ever used has the above pinout, both NPN and PNP.
-Phil
Whiteoxe, Chapter 9 of What's a Mirocontroller gives a good introduction to transistors and the 2N3904 is a very common NPN. Your meter looks like it has a diode check feature. Remember that you can think of a transistor as 2 diodes back to back.
NPN ---> N-P / P-N
PNP ---> P-N / N-P
The Base to Emitter will be one diode and Base to Collector will be the other.
A diode conducts in only one direction.
Heater, can you explain biasing because I know the resistors adjust the voltage levels but I never understood how it looked. In Parallax circuits there is usually only a base resistor but in hobby and hobby circuits there are resistors all over the place and the values can vary from circuit to circuit.
How you bias a transistor is all to do with what you want it to do. Will it just be a switch? Or a linear amplifier? Or a voltage follower? And so on.
In amplifiers you might want to set up the biasing so that the output of the transistor with no signal present sits at half the supply voltage, that gives the maximum room to wiggle up and down when delivering the output signal. That might take three resistors all ready and perhaps a capacitor. You probably want some feed back around that to control the voltage amplification and lower distortion, so there is another resistor or two and perhaps a cap.
In the case of whiteoxe and his LED we only want a transistor to work like a switch.
So first we need a resistor to limit the current through the LED. A normal white [ See edit below ] LED will consume say 10ma and require a 3v drop across it to do that. Our power supply is 6v so we need to drop 3v across that resistor. Ohms law tells us the resistor should be 300 ohms.
We put the transistor at the bottom of this chain, emitter to ground collector to LED.
Now we need to put some current through the base of the transistor to turn it on and light the LED. How much current? We put our finger in the air and guess about 250uA. Why? Because we might expect out transistor to have a current gain of about 40. One 40th of the 10ma we want in the collector is 250uA we need into the base.
Given an input signal rising to 6v Ohms law tells us what the resistor in the base should be to get 250uA. About 20K.
We build this in the simulator with a common transistor and some standard resistor values and we get this:
Poking around in the simulation we see: 9ma current through the LED, 200uA through the base resistor.
We notice that the transistor's collector gets down to 92mv and that the base is at about 700mV when the thing is on.
NOTE We have current into the base but our input signal hardly appears there as a voltage!
Edit: Changed "red" to "white". As peter points out this is a white LED in the circuit. It's data sheet indicates a 3.2 volt drop at 20ma so this circuit should be tweaked to give a 20ma load current.
You may have accidentally invented a new collective noun there. The "bench". As in a "I have a bench of transistors", "I bought a metric bench load of components".
A bit like a "bunch" more appropriate for electronic parts.
Or at least that's what I got from your thread title.
Red LEDs start conducting at 1.6V and normally drop 1.8V at 10ma or more. I use LEDs for low voltage references as they are very accurate, have a sharp knee etc. So where did you ever get a 3V figure from? That's more like a white LED.
Sorry, I was very distracted before and ready to go out, so I only quickly glimpsed the posts. I also just mentioned 3V but that was from your last post where you refer to the LED as red when that one is white.
The 2N2222 has a different pinout than P2N2222 in the TO92 package - I have been caught!
Well spotted. The NSSW008CT-P1 LED that I selected at random in LTSpice is in fact a white LED. It's data sheet suggests a forward drop of 3.2 volts running at 20ma which seems about right in the simulation. So that second circuit above should be tweaked for 20ma load.
I think my hand waving circuit descriptions still apply.
http://www.elenco.com/admin_data/pdffiles/PK-101_REV-G.pdf
Heater, I understood some of what you said.
Even fromthe stastes that postage seems very steep. I have often boughjt books from amazon, that would have weighed more than this kit and been a largewr package and Ive not paid such expensive postage. I dont think they want orders from OS.
What might be a good idea is something like this, but without having to buy the arduino with it http://www.ebay.com.au/itm/1-Set-24-Lessons-Starter-Kit-With-Motor-Relay-LCD-Servo-for-Arduino-Uno-R3-A803-/271528159477?pt=AU_Gadgets&hash=item3f3856e8f5
This is the kit I gave to my nephews , it is over $80 on aussie ebay local postage. I paid less than $40 from amazon. how do they justify that kind of markup ?