Saturating a BJT

[afesheir]

hi engineers ...

I have an 2N2222 npn BJT and I want to operate it in saturation region with supply voltage of +5V

my calculations yielded 30 Ω and 260 Ω but when using them, I didn't get satisfying results ...

can anybody can help finding these resistor values ...??

the 2N2222 datasheet is attached ...

Thanks in advance

 

[crutschow]

Need to see the circuit diagram. You don't give enough information to know what the circuit is doing.

 

[audioguru]

Your zipped datasheet is not a valid zip file so I could not open it. Attach it as the original PDF file.

I found a datasheet for the old 2N2222 from Central Semi and it shows a max saturation loss of 0.4V when its collector current is 150mA and its base current is 15mA. Then its base-emitter voltage has a max of 1.3V.

So a 5V supply and the transistor saturating with a loss of 0.4V results in 4.6V across the 30 ohm collector resistor so the current is 153mA.

The 260 ohm base resistor has 3.7V across it so its current is 14.2mA which is pretty close to the recommended 15.3mA. 260 ohms is not a 5% value. Use 240 ohms for a base current of 15.4mA.

 

[afesheir]

Need to see the circuit diagram. You don't give enough information to know what the circuit is doing.

The circuit is just a logic inverter ... and this is the circuit diagram ...
**broken link removed**

I found a datasheet for the old 2N2222 from Central Semi and it shows a max saturation loss of 0.4V when its collector current is 150mA and its base current is 15mA. Then its base-emitter voltage has a max of 1.3V.

I don't know why did the zip file failed but it is clear that the datasheet u obtained is the same as the attached one ...

thank you for ur help and i will try the new values ...

 

[audioguru]

A logic inverter cetainly does not need to have a current as high as 150mA!

 

[Hero999]

Increase the value of Rc to 4k7 and the Rb to 470R.

 

[audioguru]

Increase the value of Rc to 4k7 and the Rb to 470R.

Backwards?
Rc should be 470 and Rb should be 4.7k.

 

[Hero999]

Yes, sorry about that.

 

[ste5442]

You could also just use a FET - an FDV301N is a 'logic' FET ideal for the job.

Depending on the rest of the cct you may need a pull down on that base ;-)

S.

 

[afesheir]

A logic inverter cetainly does not need to have a current as high as 150mA!

yeah but the datasheet stated that ..??

thanks for you all for your respective replies and help ...