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Old 8th May 2011, 03:13 AM   #1
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Default CE (common emitter) Amplifier help

in a nut shell, im trying to build an amp. im using a NE5532 to take my line voltage to amplify it to 20Vp. from there i want to use common emitter using 2N2222A/2N2907 to get my rail voltages of +/-30V. From that, it will go to my main driver transistors (tip31/32) in a push-pull configuration.

I did the calculation and what not, but on my scope things aren't working as they should.

Normally I think id be able to fix this on my own but im hitting a brick wall and i know when i need to humble myself to people who may know much more.

Below is are Multisim screen shots that can help. Ill try to answer any questions you need asap.
Sadly, i cannot provide an entire schematic at this time since i dont have a scanner fr my notebook but i hope this helps:
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Old 8th May 2011, 03:27 AM   #2
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Quote:
Originally Posted by SCKentrol View Post
I did the calculation and what not, but on my scope things aren't working as they should.
I don't suppose it would. Look at what you did there: With R2= 200R and R3= 5K, you have:

V= 30(5000) / (5000 + 200)= 28.85Vdc at the base of the 2N2222. That means an emitter current of:

Ie= (28.85 - 0.6) / 1000= 28.25mA

The drop across the 15K collector resistor wants to be:

15(28.25)= 423.7V

You only have 30Vdc, therefore you've driven the 2N2222 way way way into saturation.

What, exactly, are you trying to accomplish here? If it's a simple gain stage with Av= 15, you sure don't need such huge resistors to get that much gain from a 2N2222 (or any other BJT).
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Old 8th May 2011, 03:31 AM   #3
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Quote:
Originally Posted by Miles Prower View Post
I don't suppose it would. Look at what you did there: With R2= 200R and R3= 5K, you have:

V= 30(5000) / (5000 + 200)= 28.85Vdc at the base of the 2N2222. That means an emitter current of:

Ie= (28.85 - 0.6) / 1000= 28.25mA

The drop across the 15K collector resistor wants to be:

15(28.25)= 423.7V

You only have 30Vdc, therefore you've driven the 2N2222 way way way into saturation.

What, exactly, are you trying to accomplish here? If it's a simple gain stage with Av= 15, you sure don't need such huge resistors to get that much gain from a 2N2222 (or any other BJT).
Yea, i was actually just looking over what i did, and i realized i did all kinds of stupid stuff there. lack of sleep will do that. ill repost soon with better concept >_< thanks
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Old 8th May 2011, 07:52 AM   #4
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