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DexterMccoy
03-01-2014, 10:41 PM
What is this type of transistor called, and what kind of circuit's is it used in and for?

The Transistors have a X crossing in the Servo amplifier, what does this X crossing do?

DexterMccoy
03-01-2014, 10:43 PM
here are the schematics for them

DexterMccoy
03-01-2014, 10:45 PM
This transistor has Two Emitters, look at the schematic

What is it called and what kind of circuits is it used for and why does it have 2 emitters?

DexterMccoy
03-01-2014, 10:50 PM
Servo Amp Q25 goes to Q29
and Q26 goes to Q28

What does this do? it's an X crossing pattern

shteii01
03-01-2014, 10:55 PM
That is not X crossing. There is no big black dot in the middle of the X.

What you have is two wires that run from emitter of one transistor to the base of another transistor. The two wires are not connected to each other.

DexterMccoy
03-02-2014, 12:15 AM
It seems they are used for RF modulation or modulation circuits for somereason but why 2 emitters?

shteii01
03-02-2014, 12:26 AM
It seems they are used for RF modulation or modulation circuits for somereason but why 2 emitters?
One goes to transformer, another goes elsewhere.

DexterMccoy
03-02-2014, 12:30 AM
But why use the 2 emitters to do this? for what reason?

Papabravo
03-02-2014, 05:03 AM
But why use the 2 emitters to do this? for what reason?
They are the basis of TTL circuits and perform an AND function.

DexterMccoy
03-02-2014, 05:09 PM
But why the 2 emitters? what does having 2 emitters do? why not 2 bases? or 2 collectors?

Papabravo
03-02-2014, 05:22 PM
But why the 2 emitters? what does having 2 emitters do? why not 2 bases? or 2 collectors?

Well an emitter will source current. So in a logic gate, if both emitters are high, there is no current flow from collector to either emitter and the transistor is off. This allows the collector to be pulled high.

In logic terms "A high AND a high is a high"

If either of the emitters is pulled low then the transistor is on and the collector is pulled low as well.

DexterMccoy
03-02-2014, 07:08 PM
does a Base sink or source current?
Does a collector sink or source current?

Papabravo
03-03-2014, 11:23 AM
In an NPN the base and collector will both sink current and th emitter will source current. For PNP it is the reverse.

DexterMccoy
03-03-2014, 01:19 PM
So why do they want to "choose" the pins that source current than to sink current?

They aren't using the multiple emitter transistor as an ampilifer

They are using the multiple emitter transistor as a Switch? so choosing sourcing current or sinking current shouldn't be a problem right? they could hook the signals to any pins of the transistor because it's used as a switch

DexterMccoy
03-03-2014, 01:27 PM
SERVO AMP PICTURE:

servo Amp Q25 goes to Q29
and Q26 goes to Q28

What does this do? it's an X crossing pattern

shteii01
03-03-2014, 04:30 PM
SERVO AMP PICTURE:

servo Amp Q25 goes to Q29
and Q26 goes to Q28

What does this do? it's an X crossing pattern
The two wires don't actually connect in the middle, so the current from one wire DOES NOT enter the other wire.

DexterMccoy
03-03-2014, 11:58 PM
The two wires don't actually connect in the middle, so the current from one wire DOES NOT enter the other wire.

Yes I know that, I'm not asking about that

The X crossing pattern is a push pull arrangement?

Because Q25 goes to Q29 WHY?
Why does Q26 goes to Q28?

Is this some type of push pull arrangement or what?

ifixit
03-04-2014, 01:20 PM
The circuit is an H bridge motor driver. The two sides of the "H" must work in an opposite manner with respect to each other... hence the crossover connection.

Billy Mayo
03-04-2014, 06:02 PM
Why do servo motors need an H bridge driver? What does the crossover connection do? If no crossover connection what will happen?

Papabravo
03-04-2014, 06:32 PM
The purpose of an H bridge is to steer the current through the motor coil in both directions. In one of the directions the motor moves in the clockwise direction, and in the other direction it moves counter clockwise. A uni-directional servo motor is only useful for producing a controlled velocity. For position control it is like a WOM (Write Only Memory)

shortbus
03-04-2014, 09:48 PM
Hey Dexter and Billy, will Vancastillo be joining ACC too?

DexterMccoy
03-04-2014, 11:04 PM
The purpose of an H bridge is to steer the current through the motor coil in both directions. In one of the directions the motor moves in the clockwise direction, and in the other direction it moves counter clockwise.

Thanks for the info

So what does the crossover do? why do you need the crossover?

alfacliff
03-05-2014, 12:39 PM
the two emitter transistor, or tetrode transistor was an early type used for higher frequencies than the point contact transistors of the time. google up 3n22 transistor.
cliff

Billy Mayo
03-05-2014, 01:21 PM
Do you know what kind of circuit they are used for?

alfacliff
03-05-2014, 02:09 PM
telephone company equipment and military mostly. they worked to 15 mhz according to one source on the net. that is faster than most other transistors available back then.

Billy Mayo
03-05-2014, 06:09 PM
Yes they are used in high frequency circuits it says , but what does having two emitters do? Is the 3n22 used as a switch or ampilifer? It seems that it has to have a high state on both emitters at the same,e time for it to be switched on or to amplify? If one of the emitter signals is a low state , the 3n22 will not operate?

alfacliff
03-05-2014, 06:41 PM
if you check the sources on the net, you see that it is an amplifier, the other emitter was used as a bias to increase the electron mobility to inrease hrequency of operation. back in the point contact transistor days, not very many worked as high in frequency as the am broadcast band, so they were trying things to improve frequency.

Billy Mayo
03-05-2014, 08:35 PM
I'm new to understand about how transistors are different depending on frequency? So each transistor has a range of what frequenecys it can amplify or not or their will be a roll off of gain? What determines the frequency of a transistor?

Billy Mayo
03-05-2014, 08:38 PM
My coworker said that a 3n22 is like two transistors with only one input , you drive the on input which is the base and you get two outputs