please help transistor as switch help


by michael1978
Tags: switch, transistor
michael1978
michael1978 is offline
#19
Jan2-14, 03:05 PM
P: 133
Quote Quote by Jony130 View Post
Who told you that?
Vce(sat) is always greater than zero.
See this 2N2222 datasheet
http://www.fairchildsemi.com/ds/PN/PN2222A.pdf


?? We use uppercase (capital) letters for the quantity symbols for voltage, current and power.
Also capital letter M is use in electronic as a Mega = 1 000 000 = 1M
HI
I RELLY DIDT KNOW, YOU MEAN THIS 2 parameters


I know johny, about letters, but i writte like that, but i will write good now,
you know Johny i am an amateur i like to learn electronics, the last circuit wich i send you, , why Vbe have that value? how do you calculate

Johny thnx for answer goodnight
but
Attached Thumbnails
PARAMETERS.gif  
Jony130
Jony130 is offline
#20
Jan3-14, 11:35 AM
P: 389
Quote Quote by michael1978 View Post
HI
why Vbe have that value? how do you calculate
I did not done any Vbe calculation, it is impassible to calculate Vbe and Vce(sat) voltage.
Why ? Because we don't know nothing about transistor you use in simulation. In real life we have very similar situation, and this is why we almost always use approximate value, around 0.7V.
Assuming 0.7V (or 0.65V or whatever between 0.5V....0.8V) across a forward biased silicon junction is just a rough approximation, or rule of thumb. It may be good enough for making rough estimates of circuit conditions.
Try red this :

http://electronics.stackexchange.com...-active-region
michael1978
michael1978 is offline
#21
Jan3-14, 01:51 PM
P: 133
Quote Quote by Jony130 View Post
I did not done any Vbe calculation, it is impassible to calculate Vbe and Vce(sat) voltage.
Why ? Because we don't know nothing about transistor you use in simulation. In real life we have very similar situation, and this is why we almost always use approximate value, around 0.7V.
Assuming 0.7V (or 0.65V or whatever between 0.5V....0.8V) across a forward biased silicon junction is just a rough approximation, or rule of thumb. It may be good enough for making rough estimates of circuit conditions.
Try red this :

http://electronics.stackexchange.com...-active-region
hey Johny thnx for reply, i read but is difficult to understand, but i understand you, did you hear about this book, Electronic Principles by albert malvino i like to buy this book but i dont know is good of not. i hear from one friend is good
Jony130
Jony130 is offline
#22
Jan4-14, 09:57 AM
P: 389
I measure Vbe(base-emitter voltage) vs Ib (base current) for BC337-40
The power supply voltage was Vcc = 10V

RB = 680kΩ....Vbe = 0.614V....Ib = 13.8ľA

RB = 470kΩ....Vbe = 0.616V....Ib = 20ľA

RB = 220kΩ....Vbe = 0.624V....Ib = 42.61ľA

RB = 100kΩ....Vbe = 0.639V....Ib = 93.61ľA

RB = 50kΩ......Vbe = 0.659V....Ib = 187ľA

RB = 10kΩ......Vbe = 0.719V....Ib = 928ľA

RB = 5kΩ........Vbe = 0.748V....Ib = 1.85mA

RB = 2kΩ........Vbe = 0.787V....Ib = 4.6mA

RB = 1kΩ........Vbe = 0.819V....Ib = 9.18mA

RB = 500Ω......Vbe = 0.856V....Ib = 18.29mA

RB = 200Ω......Vbe = 0.989V....Ib = 45mA

And as you can see the base current change 45mA/13.8μA = 3260 times. But Vbe change only by 375mV. This very small change in Vbe compared with the huge changes in the base current can be ignored in some cases. And this is why we use Vbe= 0.6...0.7V in hand calculations.
Also if you want to fix the issue with the bulbs, simply add resistor in series with the transistors bases. This resistors will reduce the current that is flowing through the bulbs. So the bulbs will give no light.

did you hear about this book, Electronic Principles by albert malvino i like to buy this book but i dont know is good of not. i hear from one friend is good
Yes I also heard that this is a good book, but I never read it. Why you don't buy book in your your native language?
michael1978
michael1978 is offline
#23
Jan4-14, 07:40 PM
P: 133
Quote Quote by Jony130 View Post
I measure Vbe(base-emitter voltage) vs Ib (base current) for BC337-40
The power supply voltage was Vcc = 10V

RB = 680kΩ....Vbe = 0.614V....Ib = 13.8ľA

RB = 470kΩ....Vbe = 0.616V....Ib = 20ľA

RB = 220kΩ....Vbe = 0.624V....Ib = 42.61ľA

RB = 100kΩ....Vbe = 0.639V....Ib = 93.61ľA

RB = 50kΩ......Vbe = 0.659V....Ib = 187ľA

RB = 10kΩ......Vbe = 0.719V....Ib = 928ľA

RB = 5kΩ........Vbe = 0.748V....Ib = 1.85mA

RB = 2kΩ........Vbe = 0.787V....Ib = 4.6mA

RB = 1kΩ........Vbe = 0.819V....Ib = 9.18mA

RB = 500Ω......Vbe = 0.856V....Ib = 18.29mA

RB = 200Ω......Vbe = 0.989V....Ib = 45mA

And as you can see the base current change 45mA/13.8μA = 3260 times. But Vbe change only by 375mV. This very small change in Vbe compared with the huge changes in the base current can be ignored in some cases. And this is why we use Vbe= 0.6...0.7V in hand calculations.
Also if you want to fix the issue with the bulbs, simply add resistor in series with the transistors bases. This resistors will reduce the current that is flowing through the bulbs. So the bulbs will give no light.


Yes I also heard that this is a good book, but I never read it. Why you don't buy book in your your native language?

Johny thnx for reply i understan now, but the problem in my language we dont have so much book in electronics, also in Belgium i try to find book in biblothek and in store but they explain not so good clear i mean....for example i start one course via online in holland basic electronics, but this nothing they teach you a little bit, not to do some experiments, they dont go deep in electronics, i see the last time not so long Basic Electronics, i read i little bit but pffff nothing
have a nice sleep thnx


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