Author Topic: Transistor Tutorial For Idiots, (Like Me)  (Read 809 times)

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Transistor Tutorial For Idiots, (Like Me)
« on: September 29, 2019, 08:27:30 am »
I will be Talking about a Transistor here. First, I will make this Quick. NPN Transistors and N Channel Fets has a (Faster Electron Sharing Rate) than a PNP. or P Channel. P Channel Fets Use a Negative Gate Trigger.

I will lay some math Down in due time. I will Cover some Basics Quickly here Soon. What I Will Quickly Cover for you today is the following, So that if you do not know, you will today very quickly. The point of this post is to Very quickly School Dumb Idiots Like Myself. Trust me, This stuff is not as known as you might think. Just Please Remember what I am about to post and you will be quickly cleared up on transistors if you find yourself confused quickly when trying to work with them.
This is a REDNECK Teaching by ME, This is MY stuff, Not something you will read in a book. I compiled this stuff in my brain to help me, Now it is yours to keep.

Hydrocars says this, ( Not Taught By Others) By My teachings! My Methods! Here we go;

NPN has 3 letters, the First Letter of Both (N)PN and (P)NP Idicates something, It tells you somethings.
The First Letter of the Chosen Transistor Tells you the Polarity of the (Emitter). The Rule of My Thumb is the Collector (Always Goes to the Load). With this being said, if you was confused, This should have Just Cleared it up for you.

Fact! A Transistor Needs to have a way to Shut off, Or Else it will Remain in the On State To Long, or Not Properly Perform. Always Remember A NPN Transistor Needs a Resistor Connecting Its Gate to the Negative Terminal. As  PNP Needs A resistor Connecting its Gate to the Positive Terminal to Ensure It Will Not Remain ON. Another Fact, Operating a Transistor Abover Its Saturation Point is Just Plain Usless and Stupid. You Need DataSheets to find the transistors Saturation Point for this, usually .60 Volts. Signals Such as a Microphone Must Be Between Base and Ground on a NPN Transistor, A Microphone Should Be Placed Between Base and Positive Volts on a PNP Transistor. Do Not Use PNP Type Transistors, See Google for Record Setting Transistors for Fastest Electron Rates. You will Quickly Learn NPN is the Only Option.

More Later.

Fact, Take your Saturation Base Voltage, (Redneck school here). Lets say its .65 Volts to become Saturated. Let me show you How a Redneck Makes this Happen.

Take your Supply Voltage and Divide it by 0.0001777 To get your answer. (Round The Answer you get Up Or Down to the Closest Home.) This Will Give you the Size of PotentoMeter You Need.

Say you're using 12 volts, Divide that By 0.0001777 to get 67529K ohm Pot, Round Down and use 67500 Ohms, Ad a Resistor To the Pot on the Positive Most Pot Leg for a NPN Transistor to get the Calculated Value if you dont already have the Right Pot.

To Tune The Pot.

Take the Needed Saturated Voltage From The DataSheet, In This Case 0.65 Volts and Do the Following.

Divide 0.65 Volts (Since This is what you Need at the Base, and Divide This Value By the Current Flow you used, 0.000177 to get a rounded 3600 Ohm Resistor. So Subtract 3600 from the 67500KOhm Pot and that is where your Pot shall Be set. Meaning you need 3.6K Ohms on One Side of the Pot, and 63.9K on the Other. So Now you dont even need a pot. Those are for Testing to find the Right Values.

The Above Redneck Artical Just Completely Ignored any Resistors added to the Emitter Or Collector. Take This With A Grain Of Salt.

To Find The Voltage Drop Across ANY Series Resistor, you simply Add each resistor Value to sum up the Total Resistance. Then you take that Sum and Divide it by the Target Resistance you're trying to find the Voltage Drop Across. You Dont Need To Know the Current, you will Get the current.

So, you have a total of 5 500 Ohm Resistors. Thats 2.5k Ohms, Take The sum, 2.5k Ohms and Divide it by the First 500 ohm resistor to get what I call a sub point Tracking Value( My Redneck Term.) 2500/500 = 5   Divide the Source Voltage By that (5) to get 2.4 volts if your using 12 volts for a supply, thats .024 MA, availible in this area, this can be confusing... He he..

2500 Total Ohms/the Third Resistor, and its Value is 1500 Ohms Total Resistance From Q Point as I call it, 2500/1500 = 1.666 so VSS 12V/1.666 = 7.6 Volts at this Point in the circuit, From VSS to This Point. and 2500/2000 Ohms from the Ground, =1.25, So 12 Volts \1.25 = 9.6 volts here and since its 2 Kilo Ohms you have 12/2000 .006 Milliamps at this point at 9.6 Volts, from Plus Volts To This Point in the Circuit. 

You See, You Do Not need The Current Flow to figure this out. You Can simply Get it! And Use it to Attack the Circuit Like the master you are. Last Example On this.

You have 20 Volts, and you have a series of Resistors that Equals 5000 Ohms, and You are Using 5 1Kilo Ohms Resistors. You take the Total Resistance, 5k, and you Divide that by the Total Resistace you are at in the Circuit From the ground! Say 3 resistors from Ground you are at 3000 Ohms so, Simple as Pie! Again, Do This.

Total Resistance/Target Point Resistance written as , 5000/3000 = 1.66 (Take That Number) Divide your Voltage whatever it may be (20 volts here) into 1.66 to get the Voltage Drop in that area! Wala! You just got 12 volts! because 20/1.66 is 12 volts. Guess what, You can Draw 20v/3000 .006 (6 Milliamps) From this point in the circuit from VSS to this Point.

Guess what.. at 20 Volts and a resistance of 5k ohms, According to Ohms Law you Must have 20/5000 .004 (4 Milliamps) Flowing threw All Resistors! How so?
Take the above example we used with the 3kilo ohm resistor... We know .004 x 3000ohms will give us 12 volts... So how did we determine the voltage without Ever even knowing about the total current flowing threw the total resistance?

We Used The Supply Voltage, and Resistor Values ONLY to Calculate the Voltage Drop! We did not Indroduce Current Flow Into this formula!

Every thing I just shown you, It can all be read in a Mirror! That's Right! Voltage Potential Goes Both Ways! It just Depends on where your Coming From and Where you're going!

If you dont believe me, Draw 5 resistors on a Peice of Paper, Top To Botom, Write the Voltages at each point, Write the Offered Current Flow at each Point, Write the Source Voltage on top of the Highest Vertical Resistor, and Write 0 on the Lowest Series Connected Resistor, and Read your Values and Look at it. This is All Very Basic Simple Stuff, In Fact it is so basic it is the Foundation of which electronics is Built on, Yet, Everyone So Easily over looks it, and Nobody Ever Notices it at all. I know there is some that does.

Guys, Please Start Thinking, Stop Pushing Components Together if you dont understand them. Please Read this post of mine, Please Read it until you can take a Calulator and Do just what I've shown here. I beg you if you do not understand this basic stuff, Please Please Learn it as what I have shared here is So so so easy to do but hard to remember.

Do you know what happens when you put Capacitors in series? The Capacitance is Equal to the Smallest Capacitor in the Chain! The Advantage is the Voltage Increases! Just like a Series of 400 AA Batteries, if one is Damaged the Rest Suffer!

Do you know what Happens when you Put Capacitors In Parallel? Each Time The Capacitance is Increased, C1 + C2 + C3 and so on, But The Disadvantage is the voltage can only go as high as the Lowest Voltage Rated Capacitor will let it go.

So guess what you do to solve the Problem, The Solution is just as this. Its simple.

You Get the Voltage you need!!! Then you get the Capacitance you need! Can Anyone Understand just what I said? I'm not really asking for you to answer me, Im asking you, Do you see the Parable I speak of?

Do you guy's know (and I know most of you do know this) But for you others that dont, Did you know Mosfets are Not Current Consuming Devices at their gates? They are voltage Potential Controlled only, This is why you can make a H Bridge, Look it up. You Can not do this with a Transistor, it would Blow to peices immediately! Transistors are Current Consuming Devices. I know Mosfets are sometimes Confused as a Transistor, This is not the case. When you read such Jibberish, Know Next time with Confidence, A Mosfet is NOTHING like a Transistor, It is very much Different Because it is Not a Current Controlled device!

and Just as the Transistor, Mosfets are like this...

a N Channel Mosftet has a Gate, Drain Source... a N channel Fet must have a Positive Charge at its gate to turn on in most cases, Some are Permanitly on unless you otherwise cause them to turn off.

Gate is always Opposite of its Channel, so N Channel Means it must have a Positive Gate to Operat!and you must have a method (pull up resistor) from Gate to Ground to ensure it turns off or else you will not get your signal accurate.  the Term GDS, Gate Drain Source is Just as it is ment to be. The N Channels Drain Most of the time Goes to the Load, then to VSS, and I say Most of the time because,, (since you can connect the gates Together, Unlike Transistors) In Some Cases such as the H Bridge, you will Notice why Transistors Can Not be used in Certain Cases!

The Source is Always the ground! Even if its threw the Load 2 percent of the Time, it is Grounded~ Even If It gets its ground threw the Load...

I would Like to add this, For Those that Is already using Fets, (Try using a 9 volt battery between Signal and Gate) when using inductors. (Try it) You might be amazed when you realize there was a power control there most people never knew existed!

Isolate your Heat Sink from your Fets when using a H Bridge with the proper plastic heat sinking material, or else you may be in for a surprise! and a very bad one.

I will share what I can when I can, Im sorry to be all over the place, and sorry if I seem a little bit Contradicting.

Please Understand, What I have Posted here is My Very on Personal Ways, and Learnings, they are not facts, but can be learned from. I wish I could have read this post many years ago. I have short term memory loss so I can not remember Many Formulas. I guarantee you I will Referee Back to this Very Post Monthly Probrably even Weekly to Use the information in my own post for my very on personal use just because I simply Can Not Remember.

BTW, Parallell resistors, The Formula is Basically the same for Capacitors.

You have a number of Resistors In Parallel. Quickly Find the Value. You have 4 330 Ohm Resistors, Quickly Calculate the Value. The Answer is 82.5 Ohms.

1/330+1/330+1/330+1/330 = 0.01212121212121212121212121212121
Always Use 1 an Divide it like so, 1/0.01212121212121212121212121212121 = 82.5 Ohms, That is The Same Exact Formula For Calculating Capacitors In series, It is Just that Simple.

Take the Following, 3 Capacitors, 100 UF, 400 UF and 3000 UF. You use the above formula to get a total of 77.92 UF.