right now i'm tinkering with MOSFETS and NPN Trainsistors. Focusing on transistors, more specifically the "ON Semiconductor P2N2222A NPN" According to the specs here the transistor has a maximum emitter voltage of 40VDC and a collector current rated at 600mA. So just for fun i hooked up a 12VDC motor that according to my "RIGOL DP832A Programmable Power supply" is consuming about .145 A. letting the motors run at 12V for numerous hours consuming .145A the transistor is hardly warm. On the motor i have a flywheel diode and a filtering cap however if i raise the voltage about 19.0 volts something happens to the transistor and it seems as if it shorts to the on position because when i pull the base low the motors is still running and the transistor begins to heat fast. this is especially true if i cold start the motor at 20 or higher volts. my base resistor which i blindly picked from the 2k200 OHM pile is connected to a 5VDC Source along with a 10kOHM pull_down resistor on the base of the transistor. can someone please explain to me what im experiencing here? thanks
Did you look in the datasheet of the 2N2222?
Did you measure the current of the motor at 19 or20V? You will probably have around 0,25A? Also remember that start-up current and loaed current of a motor will be a lot higher than when it's coasting with no load.
Did you measure the voltage from emitter to collector?
The breakdown voltage might be a lot higher, but did you take power dissipation into account? You cannot dissipate a lot of power in the 2N2222 before it will let out it's magic smoke!
Also, if you do not supply enough base current the transistor will not turn fully on, meaning that there will be a higher voltage across collector-emitter which means more power dissipated in the transistor, which means it will get hot and let out the smoke.
2k2 ohm might be too big a value! Maybe you need more base current.
Or you a more suitable transistor, maybe you have something in a TO-220 package?
Actually you might be on to something. I just checked the current the motor draws at 24 volts the motor was drawing about 2.1A when its stalled. When at 28VDC the motor is using roughly .250A. if i simply raise the voltage from 12 to over 21volts "Slowly" the transistor fails "as in when i pull the base low the motor continues to run slowly while the transistor heats until failure. it always fails if i start the motor at a voltage over 20VDC. i do have CHEAP RIGOL 100mhz 4 channel scope if there is something specific i could check for please tell me. so far with the scope i can tell the transistor is saturating because the collector voltage pretty much matches the emitter voltage"i say pretty much because my meter is only 2.5 digit. and the base is not floating when turned off.
from what i can tell i limited the base current to 3.0v 10mA tried a motor that uses about 200mA at 28 VDC and it would start and stop fine at those voltages until i put a load on the motor and it blows the transistor every time. i was trying to figure out if this is lack of protection circuitry or lack of transistor.
Right... Look in the data sheet of the 2N2222.
You have put a 2k2 resistor with 5V on your base, you will drop about 0.7V from base to emitter, that means that there will run about (5 V - 0.6 V) / 2200 = 2mA through your base.
Now look at the table from the data sheet about the Collector Saturation Region.
If you look at the graph for 150mA you will see that with 2mA base current you will have a Vce (collector-emitter) of about 0.15 V, which is probably okay since you will have very low power dropped, 0.15V * 0.15A = 0.0225 W.
Also in the data sheet you can see that the transistor will heat up 200 °C per Watt dissipated.
0.0225 * 200 = 4.5 °C. This is okay, and the transistor will be fine!
BUT, back to the saturation range, if you increase your collector-emitter current you will move further right on the graph, look at how far right the 500mA graph is, at 500mA your 2mA base current would create a huge voltage drop across collector-emitter! This means that at motor startup, or if you increase motor current too much you will have a dramatic heating in the transistor, probably welding collector-emitter to a short-circuit!
Try increasing base current to maybe 10mA. Or using a more suitable transistor!
wow thank you. this is exactly the information i'm trying to absorb . however i'm a bit confused when looking at the saturation region. please excuse my knowledge but can you please explain to me the collector-emitter Vce i'm confused when looking at the graph. the way im looking at it , at 2.0mA of base current at .6 volts will provide 150mA of collector-emitter saturation current? i'm pretty sure i'm wrong but i really want to know what i'm looking at
At 2mA of base current, if your collector-emitter current is 150mA, the Vce will be about 0.15V.
Vbe will be more or less constant at about 0.6-0.7V and will only vary slightly with conditions.
The graphs are at different collector currents, hence the "Ic = 1.0mA" / 10 mA / 150 mA and 500 mA graphs
I can add that the blue line in the picture i attached was something I drew to symbolize if you have a higher Vce, like 200 or 250mA, what consequence a low Ibe has to the Vce! 
When using a transistor as a switch, the dc current gain figure is of no use to you, because it
doesn't apply to saturation where the collector-emitter voltage is low.
Assume you need to provide at least 5% of the collector current into the base, maybe upto 10%.
So for a 600mA collector current, you need at least 30mA base current to get it
properly saturated - if you don't the emitter-collector voltage could rise until the base-collector
junction is reverse-biased, and the transistor will dissipate more power.
Typical Vce for saturation is 0.05 to 0.3V,
Typical Vce not in saturation, 1V or more.
The simple test is to measure the Vce voltage and check its low enough - there are usually figures
and graphs about this in the datasheet if its a switching transistor.
Also, always confirm transistor saturation with a scope.
the part i dont understand is,
""If you look at the graph for 150mA you will see that with 2mA base current you will have a Vce (collector-emitter) of about 0.15 V, which is probably okay since you will have very low power dropped, 0.15V * 0.15A = 0.0225 W.""
im not sure where you got the 0.15v from?
i think i see the 0.15v region your talking about but the way im looking at this to me it looks like the transistor is more saturated at 1.0mA than 2.0mA? surely this is not the case?
Don't be mislead by graphs, they are typical device graphs, individual variation and temperature variation
is not shown.
Stick to Ib = 1/20 Ic and you'll be fine.
Don't get the pinout confused between P2N2222A and 2N2222A.
The graphs can be a great guide of what's happening to you. Ib = 1/20 or 1/10th Ic is a great advice though, and everywhere in the data sheet where they are talking Collector Emitter Saturation voltage they have actually used Ib = 1/10 Ic! But other transistors may need even more base current or maybe much less to go into saturation.
To explain how to understand the graph I have tried doodling a bit on it.
It's plain "luck" that 150mA is actually one of the options on the graph since they have only graphed 4 different values for Ic!
If you maintain your collector current, but change your base current, Vce will change, that's basically what I'm trying to say. If you change your collector current but maintain your base current, Vce will also change!
You can imagine it like lowering or increasing your collector current basically moves the black graph left or right.
What you want to have when using a transistor to drive a load is to have a Vce as low as possible, always!
A BJT is basically a "current amplifier", you put in a current on the base and will have out "x times more current" on the collector. A MOSFET is actually similar but with the difference that it's a voltage to current amplifier (simplified), so that if you change the gate voltage you will have a change in the source current!
So both with a BJT and a MOSFET you have to pay attention to what your are doing (sufficient base current or sufficient gate voltage). That's why I suggest always look in the data sheet.
The datasheets show that for use as a saturated switch, the base current should be 10% of the max collector current.