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Please help about transistor as switch

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michael 1978 said:
please can you help, explain me in easy way this circuit
https://obrazki.elektroda.pl/2237673700_1387888073.jpg

normal must be
swith in position A
q1 on
q2 off
q3 on

switch in position B
q1 off
q2 on
q3 off
Click to expand...



When switch of q1 connected to ground, q1 could not be work so 9.20 voltage sufficient to start q2.
when q2 is working q3 won't get sufficient voltage to its base to switch ON. so, it will be switched OFF.

but when q1 connected to battery it will work as switch and at that time q2 won't get sufficient voltage at its base to on. so, it will goes off and due to this 9.98v goes to base of q3 so, it will switched ON.
 

You can perform this analysis yourself, just deducing that each transistor Q invert signal from Basis to Collector.

It means that 10v placed at any Basis, produces 0v at its collector.
Due Basis of next transistors are connected to previous transistor Collector, signal will be inverted again and ahead.

In other words, this circuit performs a cascaded inverter.




michael 1978,
Please, don´t ask for same subject on different threads.



+++
 

THNX FOR REPLY BUT HOW CAN I MAKE THE CIRCUIT TO WORK

swith in position A
q1 on
q2 off
q3 on

switch in position B
q1 off
q2 on
q3 off
THNX
 

What logic you presumed to define "circuit working" in terms of terminology ON/OFF you mentioned ?


+++
 

michael 1978 said:
THNX FOR REPLY BUT HOW CAN I MAKE THE CIRCUIT TO WORK

swith in position A
q1 on
q2 off
q3 on

switch in position B
q1 off
q2 on
q3 off
THNX
Click to expand...

The circuit should work as intended unless you have incorrectly wired them. Double check your wiring
 

andre_teprom said:
what logic you presumed to define "circuit working" in terms of terminology on/off you mentioned ?


+++
Click to expand...

yes on off

- - - Updated - - -

iimagine said:
The circuit should work as intended unless you have incorrectly wired them. Double check your wiring
Click to expand...


CAN YOU HELP PLEASE HOW TO WIRE OF IF YOU HAVE TIME TO DRAW ON CIRCUIT ON OFF ON, OFF ON OFF? THREE TRANSISTORS
 

What seems to be the problem? Have you breadboarded the circuit? What do you mean by drawing...?

PS: You can get rid of R1, it is not needed, just connect switch to ground
 

godfreyl said:
Is this what you want?

Click to expand...

YS THIS IS WHAT I WANT BUT HOW I HAVE TO CONNECT TO WORK IN YOU CIRCUIT?, i see in book they work like this but with the lamp, so is like you in circuit they work , on off on, off on off, so when i simulate they work on on on, and on on off WHY? how i have to work? thnx for reply
 

I think the problem is that you didn't fully understand the operation of the circuit. (I must confess that I also didn't realize the built-in problem at first sight).

By design, you get 9.9V across the load resistor when the transistor is "on" and still 9.3 V for Q1 and Q2 when they are "off". Only the voltage at the Q3 load resistor drops to zero in off-state. This happens because the base-emitter voltage of the succeeding stage can't rise above 0.7 V.

To get a clear off-state for Q1 and Q2, you need to add base series resistors of e.g. 10 or 20 K.
 

michael 1978 said:
when i simulate they work on on on, and on on off
Click to expand...
Are you sure?

In the picture you showed, the transistors are off on off.

If that picture is from your simulation, then it is working correctly.

To see if a transistor is on, probe the current flow at it's collecter.
 

so i have to add resistor in base? like this he doesnt work?

- - - Updated - - -

FvM said:
I think the problem is that you didn't fully understand the operation of the circuit. (I must confess that I also didn't realize the built-in problem at first sight).

By design, you get 9.9V across the load resistor when the transistor is "on" and still 9.3 V for Q1 and Q2 when they are "off". Only the voltage at the Q3 load resistor drops to zero in off-state. This happens because the base-emitter voltage of the succeeding stage can't rise above 0.7 V.

To get a clear off-state for Q1 and Q2, you need to add base series resistors of e.g. 10 or 20 K.
Click to expand...

so i have to add resistor in base? he doesnt work like this
 

michael 1978 said:
so when i simulate they work on on on, and on on off WHY? how i have to work? thnx for reply
Click to expand...

This could never be! Is this some kind of a joke? What kind of simulation software are you using? Forget about the other 2 transistor, just simulate one. See if you can manage to get it to turn on/off!
 

iimagine said:
This could never be! Is this some kind of a joke? What kind of simulation software are you using? Forget about the other 2 transistor, just simulate one. See if you can manage to get it to turn on/off!
Click to expand...
i use circuit wizard student version,

- - - Updated - - -

godfreyl said:
No.

Measure the current in the transistor collectors
Click to expand...
there is no current on transitor 1 , there is current on transitor 2, there is no current on transistor 3 when switch is in position B so off on off in position b on off onn current
 

michael 1978 said:
there is no current on transitor 1 , there is current on transitor 2, there is no current on transistor 3 when switch is in position B so off on off in position b
Click to expand...
Good. The circuit works correctly.
 

godfreyl said:
good. The circuit works correctly.
Click to expand...
yes but i read one book, he put three bubles so when i switch in position a they work q1 and q2 bubles glouw and q3 not? And in switch b 3 bubles work why?
 

What are bubles?

Can you show the circuit in the book?
 

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