voltage drop & transistor question

[Rumieus]

transistor voltage drop

what voltage drop for?
how to know which transistor to use when design circuit?
eg. 2n3404. 2n its npn,and the number?
i follow a book and design a simple circuit using multisim.. and when i want to select the transistor, i get confiused.. i dont which transistor to use..

 

[Audioguru]

what is the voltage drop of a transistor

Every transistor has a datasheet with spec's.
The 2N3904 transistor has a high current gain at a low collector current of less than 50mA.
A 2N4401 or BC337 has a much higher current gain at 50mA.

Just compare the datasheets.

 

[Rumieus]

transistor voltage loss

where do i get the datasheet for all transistor?

and voltage drop.. what its for? all the calculation for vd is used for what? tq quys

 

[subharpe]

voltage drop using transistor

Most importantly,

1. whether npn or pnp,
2. requirement of beta,
3. power dissipation: This will decide the packaging of the transistor,
4. maximum Ib and Ic.

 

[Rumieus]

transistor volrage drop

em.. that's the problem.. Beta by default is 100. The current passing through Ib and Ic is determine by R that we place in. Is that right?

So the problem is, when i try to make switch NPN circuit using Multisim, i dont know what transistor to choose..

there are a lot of transistor in multisim database.

as i stated above, if the current is decide by resistor, so it doesnt matter what transistor i choose? 2N2303 or 2N4040 as long as its NPN?

 

[Audioguru]

minimum transistor drop

hFE is used when a transistor is a linear amplifier when it has plenty of voltage between its collector and emitter.

"Max saturation voltage" is used when a transistor is used as a switch. A 2N3904 transistor has a max saturation voltage loss of 0.2V when its collector current is 10mA and its base current is 1mA. Its max saturation voltage loss is 0.3V when its collector current is 50mA and its base current is 5mA.

The datasheet has curves that show a "typical" saturation voltage loss of 0.08V when its collector current is 50mA and its base current is 5mA.
You don't know if your transistor is good or is not very good so it is best to use a base current that is 1/10th the collector current.

A 2N4401 transistor performs better than a 2N3904 at higher current.
A 2N5089 transistor has a high hFE when it has some voltage across it but its max saturation voltage loss is high at a current of 10mA and more, even with a base current that is 1.10th the collector current.

I get datasheets from www.datasheetarchive.com where I can select from different manufacturers. There are many other datasheet sites.

 

[arman_arian2005]

how to use 2n3904 in multisim

Hi

Design starts with the statement of the specification: for example u may wish to design a single stage transistor having gain 100 output resistance 1kΩ and input resistance 100kΩ. Then, assuming u choose to use a silicon BJT transistor, U could proceed to pick a suitable operating point, voltage supply, bypass and coupling capacitors, and finally circuit topology. Form these, a batch of requirements is obtained for the transistor to satisfy, like a minimum of beta, a minimum of Ic, a minimum of power dissipation capability, and a minimum of Ft. considering these, you could choose a transistor. However being familiar with the popular transistors may help U a lot because not every transistor might be available at a reasonable cost. Also, remember that operating the transistor at the verge of its power dissipation capability might not be a good idea so use transistor at least with two times power.