Transistor Guru's Needed, Help me, Help the community

[burners]

Recently I took on a rather ambitious project which entails controlling some PC fans based on tempurature and other variables.
I broke the project up into sections and have each section done except controlling the fans. What I'm confused about is Transistors in general.

Just to give some background, I'm a level 3 sys admin and am extremely knowledgable in PC's but not electronics. I have some programming background and have always had a love for electronics but only recently got into the hobby seriously.

I have read a few books to help build up my electronics knowledge and since I know VB and not C which is what most Micro's use, I have also been learning C++ and C# for use on .Net Micro controllers like the FEZ. Currently I am playing with a few Arduino's because they appear to be able to do what I want and are easy to program.

As I finish each section of my project I have been detailing the steps to post on my website so others can learn from my experience. I would like to give a lesson on Transistors for the next step in my project but I myself have some questions, so I was hoping I could get some answers from experienced individuals which effectively will be compiled into a nice lesson for others to learn from.

I understand a few things and will rattle them off as I understand them, if I am wrong please correct me. I also have some questions I would like help with.

1- I get the NPN and PNP part, from what I get NPN means a positive Base will connect the input voltage on the Collector to the output line of the Emitter, is this correct?

2- For an NPN Mosfet Transistor a positive gate will switch a negative source input connecting the Source to the Drain output, is this correct?

3- PNP would be oppisite of these, correct?

4- From what I get it seems like a transistor is used as a switch basically but what confuses me is I read something about the gate / base voltage needs to be different by an exact measure when compaired to the source voltage. Can someone explain this better?

5- For Mosfets and transistors I see some have faster switching compabilities which I get, these would be good for PWM control, what I dont get is the Voltage they are rated for. The Amperage makes sense, its the nominal and max Amperage the part can handle but the voltage on most of these are 25 Volt or 100 Volt etc.. Does this mean these can't be used for a 12 Volt source?

6- Based on this link given below what is the difference between what they categorize as a "Power" transistor and a "Mosfet" transistor? I get what each is but I thought Mosfets where best for power switching so why do these "Power" transistors make them good for power applications?
Transistor's Main Page

7- Based on the part linked below, the specs for this transistor are 50 Volt (Drain & Source), 33 Amp continuous. Does this mean I need 50 Volt or can I use 12 volt? If I can use 12 volt will the part handle more Amperage since its less voltage?
BUZ11 Datasheet

7- Based on the same part, the specs for the gate are "Gate Threshold Voltage" "min 2.1" "Typ. 3" "Max 4" "Unit V". I'm guessing this means a minimum of 2.1, typical 3 and maximum of 4 volts is needed for the gate to connect the Source with the Drain, is this correct?

I have some more questions but these are it for now.
Like I said I plan to share what I have learned which is why these questions are so broad. If your interested in my exact project and need for this knowledge I plan to be working with a 12 Volt source and I have a microcontroller which puts out 5 volt. I want to use the 5 volt line to switch on and off fans that will run on 12 volt BUT it goes deeper than that.
First I will take the incoming 12 volt and use a voltage regulator to regulate it down to 9 Volt for the microcontroller (Already built this part) then the 12 volt will branch off to a Voltage Booster which will Boost the voltage to 14 Volt.

The reason for this is because if I worked with 12 volt to the end of the circuit by the time it hit the fans it would be around 11 volt due to voltage drops and effeciency of the electronic parts, I also decided that the math for losing amperage while gaining voltage is exceptable in this case because the maximum amperage draw of the fans is far less than the power supply can put out. In other words I have plenty of amps to spare but need a few more volts.
I would like the voltage to hit the fan at around 12.4 volts max. Most PC fans can be driven with up to 14 volts and minimum 12.5 stable and safe.

From there will come the fast switching high amperage mosfets, these will be driven with PWM to switch the 5 volt or lower signal from the micro to the 12 volt or higher voltage needed for the fans. I also will add water pump support so these mosfets need to handle up to 30 watts each or aproximately 2.5 amps @ 12 volts.

Thanks Everyone

 

[audioguru]

First we must erase all your wrong ideas about how transistors operate.
But I don't want to teach everything about transistors in one reply here.
Look in Google for a good tutorial about transistors.

 

[burners]

First we must erase all your wrong ideas about how transistors operate.
But I don't want to teach everything about transistors in one reply here.
Look in Google for a good tutorial about transistors.

Done that, I've read a few chapters in books and about 20 articles on the internet on just transistors and this is where I am now.

 

[ronv]

Transistors

Sounds like you are having fun.

Recently I took on a rather ambitious project which entails controlling some PC fans based on tempurature and other variables.
I broke the project up into sections and have each section done except controlling the fans. What I'm confused about is Transistors in general.

Just to give some background, I'm a level 3 sys admin and am extremely knowledgable in PC's but not electronics. I have some programming background and have always had a love for electronics but only recently got into the hobby seriously.

I have read a few books to help build up my electronics knowledge and since I know VB and not C which is what most Micro's use, I have also been learning C++ and C# for use on .Net Micro controllers like the FEZ. Currently I am playing with a few Arduino's because they appear to be able to do what I want and are easy to program.

As I finish each section of my project I have been detailing the steps to post on my website so others can learn from my experience. I would like to give a lesson on Transistors for the next step in my project but I myself have some questions, so I was hoping I could get some answers from experienced individuals which effectively will be compiled into a nice lesson for others to learn from.

I understand a few things and will rattle them off as I understand them, if I am wrong please correct me. I also have some questions I would like help with.

1- I get the NPN and PNP part, from what I get NPN means a positive Base will connect the input voltage on the Collector to the output line of the Emitter, is this correct?

"Yes"

2- For an NPN Mosfet Transistor a positive gate will switch a negative source input connecting the Source to the Drain output, is this correct?

"Yes"

3- PNP would be oppisite of these, correct?

"Yes"

4- From what I get it seems like a transistor is used as a switch basically but what confuses me is I read something about the gate / base voltage needs to be different by an exact measure when compaired to the source voltage. Can someone explain this better?

"Most FETs require about 10 volts gate to source to fully turn on."

5- For Mosfets and transistors I see some have faster switching compabilities which I get, these would be good for PWM control, what I dont get is the Voltage they are rated for. The Amperage makes sense, its the nominal and max Amperage the part can handle but the voltage on most of these are 25 Volt or 100 Volt etc.. Does this mean these can't be used for a 12 Volt source?

"No the voltage rating is the maximum across the device."

6- Based on this link given below what is the difference between what they categorize as a "Power" transistor and a "Mosfet" transistor? I get what each is but I thought Mosfets where best for power switching so why do these "Power" transistors make them good for power applications?
Transistor's Main Page

"Sometimes on is better than the other. For example if you have 3.3 volts to turn on a power device a transistor may be easier because it only needs .7 volts on the base to turn it on whereas the FET would be harder to find at that voltage.
As power gets above a few amps FETs are better because they have a resistace drain to source as opposed to a voltage. For example a FET might have .002 ohms when on at 30 amps -- 1.8 watts whereas the transistor might be .3 volts Collector to Emitter or 9 watts."

7- Based on the part linked below, the specs for this transistor are 50 Volt (Drain & Source), 33 Amp continuous. Does this mean I need 50 Volt or can I use 12 volt? If I can use 12 volt will the part handle more Amperage since its less voltage?
BUZ11 Datasheet
"You can use 12 volts, but the amperage is limited by the power in the "on" state. You need to make sure it doesn't get to hot. Specs are usually with a really big heatsink."

7- Based on the same part, the specs for the gate are "Gate Threshold Voltage" "min 2.1" "Typ. 3" "Max 4" "Unit V". I'm guessing this means a minimum of 2.1, typical 3 and maximum of 4 volts is needed for the gate to connect the Source with the Drain, is this correct?

"Correct, but the on resistance will be higher around the theshold. You will usually see curves in the data sheet with different gate voltages."

I have some more questions but these are it for now.
Like I said I plan to share what I have learned which is why these questions are so broad. If your interested in my exact project and need for this knowledge I plan to be working with a 12 Volt source and I have a microcontroller which puts out 5 volt. I want to use the 5 volt line to switch on and off fans that will run on 12 volt BUT it goes deeper than that.
First I will take the incoming 12 volt and use a voltage regulator to regulate it down to 9 Volt for the microcontroller (Already built this part) then the 12 volt will branch off to a Voltage Booster which will Boost the voltage to 14 Volt.

The reason for this is because if I worked with 12 volt to the end of the circuit by the time it hit the fans it would be around 11 volt due to voltage drops and effeciency of the electronic parts, I also decided that the math for losing amperage while gaining voltage is exceptable in this case because the maximum amperage draw of the fans is far less than the power supply can put out. In other words I have plenty of amps to spare but need a few more volts.
I would like the voltage to hit the fan at around 12.4 volts max. Most PC fans can be driven with up to 14 volts and minimum 12.5 stable and safe.

From there will come the fast switching high amperage mosfets, these will be driven with PWM to switch the 5 volt or lower signal from the micro to the 12 volt or higher voltage needed for the fans. I also will add water pump support so these mosfets need to handle up to 30 watts each or aproximately 2.5 amps @ 12 volts.

"Pwming fans can be tricky so be careful. Here is a good link. **broken link removed** Remember the power is in the on position so it will be quite low (much less than 30 watts)"

Thanks Everyone

 

[audioguru]

The threshold voltage for a Mosfet is the gate-source voltage when it is barely turned on with a conduction current of only 0.25mA through the Mosfet's drain-source. It is actually almost turned off.
Mosfets need a lot more gate-source voltage to be fully turned on, usually 10V but 12V can be used if it is available.

 

[BrownOut]

I'll try to get the ball rolling for you:

The Amperage makes sense, its the nominal and max Amperage the part can handle but the voltage on most of these are 25 Volt or 100 Volt etc.. Does this mean these can't be used for a 12 Volt source?

The voltage is a MAXIMUM specification. So, if it says 50V, it can be used UP TO 50V, so using it at 12V is prefectly OK.

7- Based on the part linked below, the specs for this transistor are 50 Volt (Drain & Source), 33 Amp continuous. Does this mean I need 50 Volt or can I use 12 volt? If I can use 12 volt will the part handle more Amperage since its less voltage?

That's the same question, and the answer is likewise the same. Using a 50V part at 12V is acceptable.

I'll see if I can answer more when I have the time.

 

[burners]

Thanks for the help thus far, its really appreciated. I'm glad you guys are taking the time to help me instead of just telling me to search like the first guy that responded. Like I've said I have done hours upon hours of searching and reading for several days straight on this.
I even went out and bought a bunch of random NPN, PNP, MOSFET's and some voltage regulators to play with.

The MOSFET was of N type and I have a question about that, I misunderstood originally and hooked up 12V Positive on the Source and a fan on the drain and it conducted without any gate voltage, is this because I fried it open immediately from hooking up POS where a NEG should be? I thought if I smoked it I would have heard it or smelled it but nothing.

The Transistors I bought where weak so I smoked those but they worked for a minute or two, it was fun learning experience but I bought them from Allelectronics.com with some other stuff and wish I would have waited and placed my order with Futurlec instead because they are pennies on the dollar compared to allelectronics pricing on the same parts.

I'm going to possibly be placing a Digikey order soon or a Futurlec order so I will have more parts to try out and play with.
Digikey is a PITA to find parts when you dont have an EXACT need of what your looking for.
Example would be looking for the 3 Pin fan headers, I found these after about an hour of searching, and I wanted right angle headers for the board
Digi-Key - WM4641-ND (Manufacturer - 26-60-5030)
Digi-Key - WM4301-ND (Manufacturer - 22-05-3031)
**broken link removed**
Others I found, not right angle
Digi-Key - WM4201-ND (Manufacturer - 22-23-2031)
Digi-Key - WM4621-ND (Manufacturer - 26-60-4030)

After a few minutes on Futurlec I found these
Connectors - Polarized Headers - POLHDRR3

Right angle or straight and only .08 Cents each compaired to the cheapest ones on Digikey which are .35 cents each. Now I just wish Futurlec had 4 Pin female Molex connectors. This is the cheapest 4 pin Molex I can find and its $1.45 EACH
Digi-Key - WM6987-ND (Manufacturer - 15-24-4557)

 

[burners]

DAMN I just posted a big reply and when I hit post it was gone, I was using the quick reply function so maybe it doesnt work with Google Chrome browser???

Anyway, I wanted to say thank you to everyone who is helping and I really appreciate it very much. I appreciate that the other responses I received are not like the first response where someone just says search. I have already done so much searching and reading, literally for hours out of days.

So basically in my last lost message I was just saying how I bought some various transistors, mosfets and voltage regulators to play with. I believe I burnt up the mosfet which i will ask about in a second. I know I smoked a few transistors hehehe, it was good learning fun though.

Before I knew what I know now about transistors and mosfets, I hooked up a 25 volt, 25 amp N mosfet to a 12v and a fan. Now what I did was opposite of how its supposed to work, I hooked up the 12 v positive to the source and 12 volt out to the PC fan, I then grounded the gate BUT before I even grounded the gate the source and drain were already closed and power was flowing. Is this because I hooked it up wrong so it fried? I didnt hear or smell the familiar stuff so it just seemed weird. Seems it would take more than that to smoke it.

 

[shortbus=]

There is a integral diode in a mosfet that conducts when wired in reverse. No gate voltage needed.

 

[audioguru]

I began playing with electronics when I was about 8 or 10 years old, about 57 years ago.
I copied a lot of circuits by the time I was 15 and designed some when I was 17. Then I went to university to learn all the details.

You seem to have all the basics wrong and backwards.
I never fried anything because I connect parts properly. Most of the circuits I design work perfectly when first turned on or need a little tweaking. None of the many circuits I have designed have failed except for one that had a person (not me) install an IC backwards and another where a brand new Name-Brand electrolytic capacitor was shorted.

 

[tytower]

I began playing with electronics when I was about 8 or 10 years old, about 57 years ago.
I copied a lot of circuits by the time I was 15 and designed some when I was 17. Then I went to university to learn all the details.

You seem to have all the basics wrong and backwards.
I never fried anything because I connect parts properly. Most of the circuits I design work perfectly when first turned on or need a little tweaking. None of the many circuits I have designed have failed except for one that had a person (not me) install an IC backwards and another where a brand new Name-Brand electrolytic capacitor was shorted.

Ho Hum Yawnnnnn
If true then you would never have experimented ,what egotistical rot

burners - connect a multimeter set to read diodes across the various leads of a transistor. Write each connection and the result down and study it . Each transistor is two diodes .Understanding that will help and I've blown up hundreds

 

[audioguru]

Ho Hum Yawnnnnn
If true then you would never have experimented ,what egotistical rot

burners - connect a multimeter set to read diodes across the various leads of a transistor. Write each connection and the result down and study it . Each transistor is two diodes .Understanding that will help and I've blown up hundreds

No. I experimented a lot. But I experimented properly.
I have never blown up a transistor, diode nor LED. Each one has a max allowed current rating that I have seen on their datasheets and I have never exceeded.
I have also never blown the current fuse in a multimeter.

 

[burners]

I began playing with electronics when I was about 8 or 10 years old, about 57 years ago.
I copied a lot of circuits by the time I was 15 and designed some when I was 17. Then I went to university to learn all the details.

You seem to have all the basics wrong and backwards.
I never fried anything because I connect parts properly. Most of the circuits I design work perfectly when first turned on or need a little tweaking. None of the many circuits I have designed have failed except for one that had a person (not me) install an IC backwards and another where a brand new Name-Brand electrolytic capacitor was shorted.

Oh well that's great and good for you. I'm a level 3 sys admin & network engineer for Nuspire networks (the leading network security company in the US) and I taught myself to write software, at 23 I wrote several programs in a language I taught myself and put several companies out of business that made similar software. I dropped out of high school and went to college for less than a year, now I'm writing a book based on my personal life experiences entailing how someone with no college or even a diploma can reach 6 figures by the age of 30.
So now that were done measuring our dicks I'm sure your a genious in your own rights but what I'm trying to do here is help the community by making things easier to understand. I whole heartily believe that a great idea or device could be designed and made by someone with little or no electronics experience, it may not be optimal but it could be something that hasn't been thought of or just a clever way of doing something that has already been done.

I also find it odd that you say I have everything backwards yet others are saying it's correct.

Never the less I would appreciate it if you stayed out of my threads if you have nothing positive to add. If you want to bicker and be an obnoxious ******* then there are forums for that, if you want to take personal shots at me then you can send me a private message and keep it out of the forums.

 

[burners]

No. I experimented a lot. But I experimented properly.
I have never blown up a transistor, diode nor LED. Each one has a max allowed current rating that I have seen on their datasheets and I have never exceeded.
I have also never blown the current fuse in a multimeter.

You also never blew up a processor from overclocking or smoked a video card because your water cooling system leaked on it. We get it, your perfect and don't take risks in life.

I've smoked so many processors I started making key chains out of them like it was my new business, was good times. A lot of fun, something you obviously don't know much about.
So I blew up some .50 cent transistors whooooooooop-di-doooooooo-da

 

[burners]

Sounds like you are having fun.

Thanks and I checked out the maxim products you linked. I must have read a dozen articles and a few articles from others using the circuits. They seem great but one thing is the added cost and complexity if i add them to my circuits. More complexity would come from getting the microcomtroller to read the data that is meant for the LMBus. I will do some homework to see how difficult this is.

Another thing I thought is that these would be great for the Arduino duemilanove since it only has 2 interrupts which means it can only read 2 fans at a time.
I planned to use the Arduino Mega in my final work because it has 6 interrupts, the final specs would be
Read RPM of up to 6 fans
PWM control up to 12 fans (could have fans in zones)
Read up to 12 temp sensors
Display to an LCD
6 way external control
Software on Windows for software control, monitoring & alerting
And much more

The end goal is have full documentation so others can remake the project, I would also like to offer a cheap kit that will come with all parts needed (less the micro controller & LCD since LCD color and prefs vary) and including the custom circuit board for mounting the electronics. I planned to outsource the circuit board and just get a few dozen of them so I can resell them cheaper than if someone where to just buy one.

 

[audioguru]

You also never blew up a processor from overclocking

Nope.

or smoked a video card because your water cooling system leaked on it.

Nope.

We get it, your perfect and don't take risks in life.

I might be perfect. I am not stupid enough to burn out things.

I recently climbed up a very high tree to retrieve my RC electric model airplane and my wife and daughter were going to call the fire department.
I drove my new car at the fastest speed it goes (140km/hr) when the speed governor shuts off the engine.
I survived a heart attack. Then a surgeon fixed the problem.
When I was young I blew up a few electrolytic capacitors.
I made bombs that went up like rockets and my rockets blew up.
Just a few risks of many.

 

[Diver300]

Another thing I thought is that these would be great for the Arduino duemilanove since it only has 2 interrupts which means it can only read 2 fans at a time.
I planned to use the Arduino Mega in my final work because it has 6 interrupts, the final specs would be
Read RPM of up to 6 fans

While interrupts can be used, you can probably read lots of fan speeds without interrupts.

If you have programme that scans the inputs sufficiently quickly, and notes the time when the signal has changed, you can read the speeds effectively.

 

[burners]

While interrupts can be used, you can probably read lots of fan speeds without interrupts.

If you have programme that scans the inputs sufficiently quickly, and notes the time when the signal has changed, you can read the speeds effectively.

I was able to do something like this when the code was simple and didn't do much else besides read RPM but after all the other code is added it becomes a huge timing issue and then anytime the code is changed the timing is thrown off again.

 

[Diver300]

You need to have a hardware timer running. As long as you can scan the inputs fast enough, when a fan input changes, you can read the timer and work out how fast the fan is running.

 

[burners]

You need to have a hardware timer running. As long as you can scan the inputs fast enough, when a fan input changes, you can read the timer and work out how fast the fan is running.

Is this something the Arduino would be capable? I know it has some time functions and the way I had this working before was something like so

wait 10 milliseconds
check input 1
check input 2
check input 3
check input 4
check input 5
check input 6
Record 0 or 1 in a variable set for each input if the value is high

Do this function 100 times and then take each variable value x 60 and that would be approximately the RPM of the fan if the divider is 1

Now the problem comes as I add code because reading the inputs and doing other things take time, so although the code I posted above would be very accurate once I added more code and functions that take 1-10 milliseconds that is time lost and the average would no longer hold true.

Now on the other hand if I use external interrupts the input is read constantly while other code is running and if the input goes high the value is wrote in the background while other code is running.

Can you give me a good example of reading RPM with a timer that wont be effected by other code?