Author Topic: Pulling my hair out here ....  (Read 2261 times)

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Offline RtwoTopic starter

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Pulling my hair out here ....
« on: November 30, 2019, 09:04:43 pm »
... OK, I don't have much left so not really  :)

But I'm certainly getting frustrated at where I'm going wrong with this common emitter amplifier circuit.
12VDC powering the circuit
1KHz/1V signal going into the base from a function generator

Could someone give me a clue where to start looking at why I'm just not seeing an amplified signal out?
I've replaced all the components a couple of times in case I've fried them .... I'm stuck ...................HELP

Breadboard


Input


Output
 

Offline StillTrying

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Re: Pulling my hair out here ....
« Reply #1 on: November 30, 2019, 09:21:39 pm »
I can't see an obvious fault on the breadboard, are the emitter and collector inserted far enough in to the board.

DC measurements such as checking there's some voltage across the 220R emitter resistor, and that the base is 0.6V higher than the emitter should find it!
.  That took much longer than I thought it would.
 

Offline silverback

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Re: Pulling my hair out here ....
« Reply #2 on: November 30, 2019, 09:23:40 pm »
Cannot clearly see if the capacitor from the collector is connected to the output.
 

Offline RtwoTopic starter

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Re: Pulling my hair out here ....
« Reply #3 on: November 30, 2019, 09:27:00 pm »
I can't see an obvious fault on the breadboard, are the emitter and collector inserted far enough in to the board.

DC measurements such as checking there's some voltage across the 220R emitter resistor, and that the base is 0.6V higher than the emitter should find it!

thanks, I'll double check
 

Offline RtwoTopic starter

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Re: Pulling my hair out here ....
« Reply #4 on: November 30, 2019, 09:27:45 pm »
Cannot clearly see if the capacitor from the collector is connected to the output.

Yeah, it definitely is - poor photo
 

Offline nali

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Re: Pulling my hair out here ....
« Reply #5 on: November 30, 2019, 09:36:20 pm »
1nF input/output cap is too small - at 1kHz it will have an impedance of 159k so your 3k3//20k biasing resistors will squash any AC input signal. Try something in the uF range.
 

Offline RtwoTopic starter

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Re: Pulling my hair out here ....
« Reply #6 on: November 30, 2019, 09:49:21 pm »
OK thanks

More things to try tomorrow  :-+

 

Offline andy3055

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Re: Pulling my hair out here ....
« Reply #7 on: December 01, 2019, 12:07:06 am »
I can hardy make out the transistor orientation. But I feel your collector and the emitter is switched. I may be wrong though. :-//

Most of the resistor leads seem to be stretched all the way. Are they making proper contact in the b/board?
« Last Edit: December 01, 2019, 12:09:20 am by andy3055 »
 

Offline Dacke

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Re: Pulling my hair out here ....
« Reply #8 on: December 01, 2019, 01:54:06 am »
Just a quick thought.  Some of the resistor leads are a bit long.... When you got them,  did you pull them out of the adhesive tape that sticks them together or did you cut the ends of the leads off just before the tape?  If it's the former,  that adhesive residue can stick to the leads and cause bad connections in a breadboard.
 

Offline not1xor1

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Re: Pulling my hair out here ....
« Reply #9 on: December 01, 2019, 06:56:18 am »
Do you know what "subject" means?
Please edit your thread subject
 
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Offline LateLesley

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Re: Pulling my hair out here ....
« Reply #10 on: December 01, 2019, 10:10:09 am »
I'll second what silverback says. That output capacitor is not connected to the pin with the yellow wire.

The output capacitor is connected at row 14 - row 13, but the pin and yellow wire are on row 12, unconnected.

At least from what I can see in the pic.
 

Offline austfox

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Re: Pulling my hair out here ....
« Reply #11 on: December 01, 2019, 02:37:15 pm »
I agree with Andy that you have the collector and emitter around the wrong way. Emitter (pin 3) should be going to ground, looks like it is going to 12V.
 

Offline g0mgx

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Re: Pulling my hair out here ....
« Reply #12 on: December 01, 2019, 03:00:33 pm »
Looks like the output cap is connected to fresh air.

I really dont like the 2 separate resistors in the same hole connecting to the base either.
 

Offline RtwoTopic starter

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Re: Pulling my hair out here ....
« Reply #13 on: December 01, 2019, 06:42:55 pm »
Plenty to look at, thanks all

Unfortunately I've not had time today to look at it further.
I'm now away at work until Christmas so I'll revisit it then.
 

Offline Rigolon

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Re: Pulling my hair out here ....
« Reply #14 on: December 03, 2019, 01:22:08 pm »
I agree with Andy that you have the collector and emitter around the wrong way. Emitter (pin 3) should be going to ground, looks like it is going to 12V.

Transistor seems to be OK. 2n2222a pinout is Emitter (1) - Base (2) - Collector (3).
Emitter will be pin 3 with the p2n2222a (PNP transistor)

But I agree that output capacitor is not connected with yellow wire and test pin. That should be your problem, and I didn't do the math but double check if you are biasing your transistor correctly.
 

Offline austfox

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Re: Pulling my hair out here ....
« Reply #15 on: December 04, 2019, 08:10:24 am »

Transistor seems to be OK. 2n2222a pinout is Emitter (1) - Base (2) - Collector (3).
Emitter will be pin 3 with the p2n2222a (PNP transistor)
.

Oops, I was indeed looking at the P2N2222A datasheet. It seems both are NPN transistors. To cause even more confusion, at least one retailer is linking their 2N2222As to a P2N2222A datasheet.
« Last Edit: December 04, 2019, 09:24:41 am by austfox »
 

Offline Jwillis

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Re: Pulling my hair out here ....
« Reply #16 on: December 05, 2019, 07:25:28 am »
The P2N222A and 2N222A are both NPN . The only difference is the PN222A is a plastic case and the 2N222A is a metal case. You have the plastic case . Pin 1 is collector ,2 Base and pin 3 Is the emitter.

2N222A https://www.onsemi.com/pub/Collateral/P2N2222A-D.PDF

P2N222A https://media.digikey.com/pdf/Data%20Sheets/ST%20Microelectronics%20PDFS/2N2219A,%202N2222A.pdf

Besides you take you out put signal from the collector not the emitter.

your transistor is backwards
« Last Edit: December 05, 2019, 07:43:24 am by Jwillis »
 

Offline mikerj

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Re: Pulling my hair out here ....
« Reply #17 on: December 05, 2019, 09:03:41 am »
The P2N222A and 2N222A are both NPN . The only difference is the PN222A is a plastic case and the 2N222A is a metal case. You have the plastic case . Pin 1 is collector ,2 Base and pin 3 Is the emitter.

For extra confusion, there is also the PN2222A that uses the more common EBC pinout.
 

Offline Ed.Kloonk

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Re: Pulling my hair out here ....
« Reply #18 on: December 05, 2019, 09:04:25 am »
Do you know what "subject" means?
Please edit your thread subject

Being that it was posted in Beginners area of the forum, what did you honestly really expect them to say?

iratus parum formica
 

Offline austfox

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Re: Pulling my hair out here ....
« Reply #19 on: December 05, 2019, 11:04:50 am »

Being that it was posted in Beginners area of the forum, what did you honestly really expect them to say?

Maybe ‘Problem with my common emitter amplifier circuit’.

They have a scope so are probably a bit more advanced than a true beginner.
 


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