Can you post a diagram of your test circuit, voltages, test points etc?

 

Can you post a diagram of your test circuit, voltages, test points etc?

I'll try to remember exactly what I did and replicate it in a simulator.

Meanwhile... then is it? is hFE supposed to be the ratio between base-emitter current and collector-emitter current?

as in: base-emitter current X hFE = collector-emitter current

 

What I did was to first calculate the resistance to get the desired base current, which I decided it should be 20mA from a 3v DC power supply. I deducted the 0.7v from the base-emitter from the 3v and divided it by the 20mA to get the resistance, which came to 215Ω (I used 2 x 220Ω resistors in parallel as it was the closest I could get)... and put it all together in this way:

Than measured the current going into the collector and divided it by the measure I got for the current going into the base; the result was around 40. The results above is not what I got, that's what the simulator gives me with virtual components.

 

Forget about it; just did the test again and the current through the collector is more than what my multimeter can measure (more than 200mA).

I probably did something wrong the other day.

 

I think I burnt the transistor; it's not working any more.

And the other BC547C I have, which is the one I used the other day, must also have something wrong, because it gives me the wrong results again: 15 times more current on the emitter than in the base.

But the multimeter is testing both as good.

 

I would suggest using a higher voltage supply (12-15 volts) so you have some more range to play with.

 

What I did was to first calculate the resistance to get the desired base current, which I decided it should be 20mA from a 3v DC power supply.

A BC547, according to the datasheet, has an absolute maximum DC collector current of 100mA. The minimum DC current gain is 110, so that means the maximum base current should be 100mA/110 = 0.9mA.

hFE is rarely used directly as a value circuit performance depends on since it varies so much between devices. You should first think of what you want a circuit to do, then ask questions about the best way to go about it. If you just want to investigate the current gain of a transistor out of curiosity, you will get wildly differing results that don't have as much impact on real circuits as you might think.

 

I'm not currently making anything, just investigating the hFE out of curiosity.

The circuit I did should have sent a minimum of 1.8 AMPS through the collector... with a maximum of 100mA no wonder why it burnt.

And there also must be something wrong with the other BC547C; it just multiplies the base current by 15 in my test circuit, the same circuit that burnt the previous transistor. But the multimeter is still testing it as 650 hFE.

I'll try it again tomorrow with another set of transistors...

 

How much current can your 3VDC supply deliver?

 

How much current can your 3VDC supply deliver?

It's regulated. I kept on going up until it passed 200mA, then lost track because I was in the 200mA range in both the power supply and the meter... and that's when suddenly the transistor stopped... well, transisting.

 

and that's when suddenly the transistor stopped... well, transisting.

The technical term is transistor'ing. HA! Just kidding It's probably in saturation.

 

In your test setup add a resistor between the collector and V+.
Calculate it to allow the max current the transistor can handle.
There is also a power calculation at work here. (volts x current)

There's no better way to learn than to make components stop
component'ing once in a while.

 

I'm not bothered about using other people's designs; it's about not having to look for a circuit every time I need to do something -you need to know its name, how it works, where to find it, how to modify it, etc- a lot of knowledge that I don't have and that I didn't thought was necessary;

Hi, that is my problem too. Now I am trying to learn every basic circuits and know deeply how it work and I can draw it on my own.

 

Hi, that is my problem too. Now I am trying to learn every basic circuits and know deeply how it work and I can draw it on my own.

I'm about to start from the point were I left it in my last course: power supplies, which was the first circuit on the program. I found my old electronics book and going to start with it, then check out these 2 websites for basic circuits:
Basic Electronics Tutorials and Revision and, of course, All About Circuits. Then I'll continue with this one which has many books on practical circuits with explanations of how they work: Talking Electronics.

If any of you know other websites or ebooks explaining very basic circuits, please let me know.

The technical term is transistor'ing. HA! Just kidding It's probably in saturation.

In your test setup add a resistor between the collector and V+.
Calculate it to allow the max current the transistor can handle.
There is also a power calculation at work here. (volts x current)

There's no better way to learn than to make components stop
component'ing once in a while.

I'm sure that will not be my last transistor that stops transistor'ing. Maybe the BC547 is not the idea transistor for me to play with.

I think that were I made the mistake was in setting the base current on 20mA -apart from not checking out what's the maximum that can go through the collector-. I mean, If I was expecting those 20mA to be multiplied by 650 that would have given me 13A, which is 6 times more than what my power supply can supply. I should have calculated the base current to be 0.15mA in case the experiment worked and I got the 100mA on the collector.

If I used a collector resistance, that would be limiting the current and wouldn't be able to check if the ratio was correct; Am I right?

 

Hello,

You might also like the pages of the EDUCYPEDIA:
http://educypedia.karadimov.info/electronics/electronicaopening.htm

There you will find a lot of linkpages with information on all kinds of electronics subjects.

Bertus

 

Hello,

You might also like the pages of the EDUCYPEDIA:
http://educypedia.karadimov.info/electronics/electronicaopening.htm

There you will find a lot of linkpages with information on all kinds of electronics subjects.

Bertus

Thanks... it looks more advanced than the other 2 but also more complete in terms of circuits. I'll add it my bookmarks and leave it for when I finish the other 2.

 

I'm about to start from the point were I left it in my last course: power supplies, which was the first circuit on the program. I found my old electronics book and going to start with it, then check out these 2 websites for basic circuits:
Basic Electronics Tutorials and Revision and, of course, All About Circuits. Then I'll continue with this one which has many books on practical circuits with explanations of how they work: Talking Electronics.

If any of you know other websites or ebooks explaining very basic circuits, please let me know.





I'm sure that will not be my last transistor that stops transistor'ing. Maybe the BC547 is not the idea transistor for me to play with.

I think that were I made the mistake was in setting the base current on 20mA -apart from not checking out what's the maximum that can go through the collector-. I mean, If I was expecting those 20mA to be multiplied by 650 that would have given me 13A, which is 6 times more than what my power supply can supply. I should have calculated the base current to be 0.15mA in case the experiment worked and I got the 100mA on the collector.

If I used a collector resistance, that would be limiting the current and wouldn't be able to check if the ratio was correct; Am I right?

The collector resistance does limit the current, but only to a safe value.
If gain ~ 100 and you put 0.1 ma into the base, you would expect ~ 10 ma C-E.

If you have a 100 ohm collector resistor, what would happen ?
Then try 50 ohms, 200 ohms.

 

The collector resistance does limit the current, but only to a safe value.
If gain ~ 100 and you put 0.1 ma into the base, you would expect ~ 10 ma C-E.

If you have a 100 ohm collector resistor, what would happen ?
Then try 50 ohms, 200 ohms.

I see what you mean now.

 

One question... anyone knows of a good video or series of videos explaining all these fundamental circuits that I need to study?

Most I found deal mainly with individual components and laws.

 

Hello,

Learnerstv has a lot of engeneering lecture series:
http://www.learnerstv.com/Free-Engineering-video-lecture-courses.htm

Bertus