I like problems that have lights in the circuit so I can see if it works.
Anyhow, this is what I am working on and I cannot get the micro amp meters to move.
I have torn it down and rebuilt it 3 times and still no love.
I have taken meter readings at various points but frankly I don't know what is correct or not.
I don't have a 1m pot so I substituted a 1m resistor.
The voltage reading that I get, emitter to collector, is 9v and I suspect that it is wrong but dont really know.
So, could someone tell me where to take readings and what to expect?
Thanks.

 

How is your milliammeters positioned? They are in the circuit, not just a temporary parallel connection like a volt meter. They MUST be the only path for current to flow because, unlike a high resistance volt meter, an ammeter is very low resistance.

 

As drawn your base current will be about 8.2 uA assuming as Gopher mentioned your uA meter is in series and assuming the potentiometer is 1 Meg Ohm. What were you expecting to see and what is the range of the microampmeter?

Ron.

 

1. Did you measure the voltage of 9V battery?
2. Do you know the resistance of the micrometer?
You could try other way to get the uA current, that is to use the millivolts meter cross on 10K to get the voltage and calculates the current I = V/R.

 

Let's take a quick estimate of what the collector-emitter voltage would be for the given circuit.

Your base current will be about 9 μA (9V / 1 MΩ). Assuming a β of 200, that means that the collector current will be about 1800 μA, or call it 2 mA. That means that the voltage across the collector resistor will be roughly 1 V. So your collector-emitter voltage should be something in the 8 V range. But if the β of the transistor were only 100, you'd be in the 8.5 V range. Your base current is actually going to be less than 9 μA, so that will push the Vce even higher. If you 9 V battery is nice and fresh it might have a voltage greater than 9 V, meaning that a Vce reading of 9 V does not necessarily mean no collector current.

So while I would expect you to see something a bit less than 9 V, I can't completely rule it out.

What voltage do you measure across the collector resistor? This is generally a better way of getting a current measurement.

Put several of your 1 MΩ resistors in parallel to get you some decent base current flowing. Do you have any resistors that are in the 10 kΩ to 100 kΩ range?

 

I like problems that have lights in the circuit so I can see if it works.
Anyhow, this is what I am working on and I cannot get the micro amp meters to move.
I have torn it down and rebuilt it 3 times and still no love.
I have taken meter readings at various points but frankly I don't know what is correct or not.
I don't have a 1m pot so I substituted a 1m resistor.
The voltage reading that I get, emitter to collector, is 9v and I suspect that it is wrong but dont really know.
So, could someone tell me where to take readings and what to expect?
Thanks.View attachment 140216

It was more common with European transistors - but some types can have a choice of pin layouts.

A DMM diode check function can identify the 2 P/N junctions, but not tell the difference between collector and emitter - getting those the wrong way round should just cause very low gain.

 

It was more common with European transistors - but some types can have a choice of pin layouts.

A DMM diode check function can identify the 2 P/N junctions, but not tell the difference between collector and emitter - getting those the wrong way round should just cause very low gain.

I hadn't thought of that -- I always assume that people check their pinouts when something doesn't seem right. But newbies often don't and it's not unreasonable for them to think that all transistors in the same case should have the same pinout (because, damn it, they SHOULD!). This could well be the problem.

 

I will have to wait until tomorrow to get back to it but some things i can answer. The 9v supply is rock solid from a desktop power supply. I am reasonably certain that i have the micro amp meter connected in series correctly. I have triple checked it and will do so again.
I have a lot of resistors so can put together pretty much any combo.
I seem to remember that I tried it with 500k, as well as 100k, with no difference.
What would happen if I had the collector and emitter reversed ? I don't think that i do but stranger things have happened.
I also read that the base voltage should be 5v. Though I don't know if that was a max, ideal, or turn on voltage.
Does that mean that this transistor will act as a switch, 5v, passes current, anything less is nada.
Lots to learn.

 

I hadn't thought of that -- I always assume that people check their pinouts when something doesn't seem right. But newbies often don't and it's not unreasonable for them to think that all transistors in the same case should have the same pinout (because, damn it, they SHOULD!). This could well be the problem.

American transistors usually have the same BCE layout as Asian transistors - but neither are 100% in every case.

Some American transistors have the option of European EBC layout. Some RF transistors have a different layout.

 

I will have to wait until tomorrow to get back to it but some things i can answer. The 9v supply is rock solid from a desktop power supply. I am reasonably certain that i have the micro amp meter connected in series correctly. I have triple checked it and will do so again.
I have a lot of resistors so can put together pretty much any combo.
I seem to remember that I tried it with 500k, as well as 100k, with no difference.
What would happen if I had the collector and emitter reversed ? I don't think that i do but stranger things have happened.
I also read that the base voltage should be 5v. Though I don't know if that was a max, ideal, or turn on voltage.
Does that mean that this transistor will act as a switch, 5v, passes current, anything less is nada.
Lots to learn.

The base to ground voltage is likely 0.6 to 0.7 (a diode drop), current into the base will determine the max possible current from emitter to collector(which can be further reduced by your 510 ohm resistor.

Use ohms law to estimate current into base. 9v - 0.6v

If you have C and E reversed, you'll have a gain of about 1 instead of 100. No damage. Just turn it around and try again.

 

Also, make sure your 1M ohm potentiometer is wired correctly. You are wiring it as a rheostat (current limiter instead of voltage divider).

 

Note that, at the present time, he is not using a pot at all, but substituting a fixed resistor for it.

But it's a good heads up for if/when he gets a pot.

Right now my money's on a reversed or damaged transistor.

@Hextejas : Your original schematic indicates a 2N3904 transistor. Is that actually the transistor you are using? What is the case style?

 

Have you tried other corrent measurements with the meter? It could have a blown fuse.

Bob

 

It is a 2N3904, T-92 pkg.
I tried swapping it out for a 2N2222 and it made no difference. I might try a different breadboard cause this is a new one and is difficult to insert stuff into it.

 

As BobTPH suggests, do verify that your meter works. Put it in series with just the 9 V supply and the 1 MΩ resistor and see if you get something near 9 μA. Do the same with the meter (or range) you are using in the collector leg using a 10 kΩ resistor and see if you get something on the order of 0.9 mA. Blown meter fuses are a common problem. I tend not to think of this issue because I don't think I have a single meter that does NOT have a blown fuse, but since I always measure current using a current-sensing resistor and a voltmeter, it doesn't bother me.

 

Just read the voltage across the resistor

 

I hadn't thought of that -- I always assume that people check their pinouts when something doesn't seem right. But newbies often don't and it's not unreasonable for them to think that all transistors in the same case should have the same pinout (because, damn it, they SHOULD!). This could well be the problem.

How do I check the pin out ? Is there a way to use a multimeter to do this ?
Thanks

 

https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07


2N2222 and 2N3904 in plastic packages will be have the leads arranged like this (above).

 

https://vetco.net/blog/test-a-transistor-with-a-multimeter/2017-05-04-12-25-37-07

View attachment 140287
2N2222 and 2N3904 in plastic packages will be have the leads arranged like this (above).

That image assumes you have the pins pointing UP to you.

 

That image assumes you have the pins pointing UP to you.

I've always hated that the pinout images aren't more obvious. I prefer ones like this that leave no room for doubt: