Maker Pro
Maker Pro

Electronic Parts [Explained] pls..

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
i learned from that site that the small current or voltage applied to the base the larger the voltage is allowed to flow on the other two leads, but what does collector and emitter will do? I did not get your point there sir. More details pls
 

davenn

Moderator
Sep 5, 2009
14,254
Joined
Sep 5, 2009
Messages
14,254
i learned from that site that the small current or voltage applied to the base the larger the voltage is allowed to flow on the other two leads, but what does collector and emitter will do? I did not get your point there sir. More details pls

Voltage doesnt flow :) its the current that flows

OK for a NPN type transistor, the collector will be going to + Volts possibly via a resistor or other load
The emitter will be going to -Volts
Think of the contact point between the collector and emitter as a one way valve and the base as a tap. As you increase the voltage to the base (turn the tap on a bit more), it opens the collector emitter valve a bit more and alows more current to flow
Decrease the base voltage and the collector emitter valve closes a bit. Drop the base voltage below 0.6V and the valve closes completely

Dave
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
omg! What a simple explanation.

now i know! I love you! Hahahaha.

ok now that i know how it works,
can you tell me how to control the base voltage?
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
hey guys, guess what?

i reviewed all of these and cant believe that i did improve about these things.. thanks to you again. but still bit confuse.. just still maybe i need to reread it again.. hahahaha..

can you now tell me on how to make my own design? as usual my favorite an amp.. any amp (im referring to power amp) and powered by batter.. i want to practice with batteries first before going to ac supply coz im afraid getting electrc shock
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
can you tell me how to control the base voltage?

You don't.

Essentially the base voltage will rise from zero up to about 0.6V before anything happens and then it stays relatively constant.

It it the current flowing into the base that is the issue.

How do we amplify voltages then? (since that is typically what we want to do)

The answer is... use a resistor!

If we have a voltage which varies between 1 and 2 volts and we place a 1k resistor between that and the base. Now the current will vary between (1-0.6)/1000A (0.4mA) and (2-0.6)/1000A (1.4mA).

That change in base current may allow a collector current (say) 100 times larger. So that's 40 to 140mA. If that flows through a 50 ohm resistor then we have a voltage swing of 5V at the output.
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
Wait wait wait.. Should i use ohm's for that??

Let's say i have 9v and need a 0.6v then i would use R=V/I right?? But how much current do i need??
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
Wait wait wait.. Should i use ohm's for that??

Let's say i have 9v and need a 0.6v then i would use R=V/I right?? But how much current do i need??

That question doesn't make sense.

To use Ohms law you need to have two of V, I, and R, and want the third one.

So if you have a 9V signal, and you want to get 0.1mA of current into the base of a transistor, THEN you can ask what value resistor to use.

In this case the voltage across the resistor will be 8.4V (approximately) and the current is 0.0001A, so the resistance is 8.4/0.0001 = 84000 ohms (84k)
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
No no wait wait, i asked a not so clear question

Wht i mean is, how much current do i need to activate the transistor.. Do i need to look on its datasheet?

I know how to use ohm's law now... To find its resistance i need to know the I and the V first.. But in this case i dont know thr current that's what im asking... Is it more clear now?
 

(*steve*)

¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd
Moderator
Jan 21, 2010
25,510
Joined
Jan 21, 2010
Messages
25,510
Wht i mean is, how much current do i need to activate the transistor.

More than zero.

Essentially, the collector current will try to be the base current times the gain of the transistor.

The transistor's gain will vary with current, and the datasheet will tell you that.

What you do is:

1) determine the collector current you require
2) determine the gain of the transistor at that collector current
3) determine the bas current required (collector current divided by gain)
4) apply any fudge factors (advanced)
5) determine how to get that base current (it is often just calculating a resistor value)
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
Omg steve never knew that transistor is so easy as 1 2 3

Why didnt you tell me that before.. Wahahahaha i learned a lot again today

So to find out how much base current is needed i need to find the gain and the collector currrent and divide the collector current by gain which i can find on the datasheet.. Is that right??

So how would find the gain?? Is there a formula or is it written on the datasheet??
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
What a noob question.. Well maybe its becoz i did not know this before

Uhm question again, what is the current of an audio signal like a guitar's signal? So i know what transistor to use..
 

CocaCola

Apr 7, 2012
3,635
Joined
Apr 7, 2012
Messages
3,635
Uhm question again, what is the current of an audio signal like a guitar's signal?

VERY VERY low, and fully dependent upon how fast the strings are vibrating, how many are vibrating at any given time and the design of the pickups... That is unless the guitar has an internal power source and amplifier...
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
Aw c'mon so you mean i'll just assume it?? How would i know?? Oh wait, ok let's say it is amplifed already.. The current went out to the collector, is there a difference between 100 and 200 amp?? What i mean is will it make it louder? More sensitive to strings vibration (gain)?? I know i can control the output by controlling it with a resistor after the collector.. But what's the difference??
 

CocaCola

Apr 7, 2012
3,635
Joined
Apr 7, 2012
Messages
3,635
Aw c'mon so you mean i'll just assume it??

No you measure, there are lots of varibles and no one can give you the answer as no single answer exist... Let's equate this to how many miles per gallon does a vehicle get, do you have an answer?

How would i know??
You measure or find technical data from someone that measured...

is there a difference between 100 and 200 amp??
Of course there is a difference between 100 and 200, that is preschool level math...

What i mean is will it make it louder?
About 1/10 louder to the human ear between 100 and 200 Amps, if all else remains the same...

More sensitive to strings vibration (gain)??
Electric guitars produce a very small amount of electricity as the string vibrates over a magnetic coil (pickup)... The more they move the more electricity they make...

I know i can control the output by controlling it with a resistor after the collector.. But what's the difference??
You are now talking about a amplifer, not what the guitar itself is doing...
 

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
Seems like you are frustrated and mad at my noobidity..

So high gain would be louder... Ok now it is answered. Now im done on collector and gain thing and about the base current i need.. Next thing is emitter.. What does it do?? The base is amplifie on the collector by the gain but what about the emitter???
 

CocaCola

Apr 7, 2012
3,635
Joined
Apr 7, 2012
Messages
3,635
Seems like you are frustrated and mad at my noobidity..

Don't confuse or equate you not liking the answer or not understanding the answer to me being frustrated, you are so far off on said comparison that it's hardly worth my acknowledgment...
 

CocaCola

Apr 7, 2012
3,635
Joined
Apr 7, 2012
Messages
3,635
Ok.. Hmm can i use a multimeter to measure the guitar's input current?

You mean output current? This is a factor of mostly the number and size of the windings on the pickups and the degree of movement of the strings... Just like the voltage output from these coils the current also varies all over the place, it's not a constant... And just like my vehicle analogy EVERY coil type and brand will produce different values...

As for how to measure you would use an AC ammeter that measures real low currents, from what I gather you are in the nanoamps range, aka not practical for most people to measure without costly equipment...

I'm not sure where you are going with this though...
 
Last edited:

electronoobz

Jan 14, 2012
226
Joined
Jan 14, 2012
Messages
226
Ok forgot those current, i'll just a low-noise high r low gain (depends on what i want) transistor to make an amp

Ok so to start on let's i have 9v battery and the the guitar's output

Should i do this?

9v + guitar's output ==> biasing resistor ==> transistor's base

Or

9v ==>biasing resistor ==> guitar output + transistor's base??
 
Top