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SMPS's with cascoded opto feedback

davenn

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So you're telling me that you have a series circuit where the current at one point differs from the current at another point. And to be clear, we are talking frequencies where the wavelength is HUGE compared with the size of the circuit (essentially DC).

that's pretty cool :rolleyes: and breaking a few laws along the way haha

Dave
 

(*steve*)

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I did a similar experiment with a BFX43, base left open. Maybe I had the setup wrong but I followed what Steve was doing apart from having two power supplies.
what do you think.

Try reversing the oscilloscope probe's connections. I found that my "floating" power supplies actually have some capacitance between the negative rail and ground. This, when coupled with the probe's connection to ground asymetrically loaded the two configurations resulting in a slower rise time when the probes were connected one way vs the other.
 

Arouse1973

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I have my good scope back now so I can invert the signal. Have to wait till next week. But yes Steve this could be the issue.
Adam
 

Arouse1973

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So you're telling me that you have a series circuit where the current at one point differs from the current at another point. And to be clear, we are talking frequencies where the wavelength is HUGE compared with the size of the circuit (essentially DC).

Hi Steve. I didn't say that, you know it's a photo transistor with a resistor connected to the collector. People might mock me on here but I can only state what I understand and back it up with experiments. But I am always prepared to be proven wrong, but need hard evidence I can understand to get my head around it.
Cheers
Adam
 

(*steve*)

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Hi Steve. I didn't say that

Forgive me. I thought you said you measured the emitter current and the collector current (with the base open) and found there was a difference.
 

(*steve*)

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I have my good scope back now so I can invert the signal. Have to wait till next week. But yes Steve this could be the issue.
Adam

In my case I solved it by making sure the scope's ground leas was attached to a supply rail. But while I think that's a universal solution, I also have a battery powered scope that I can pull out if required. It's only single channel though.
 

KrisBlueNZ

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Try reversing the oscilloscope probe's connections. I found that my "floating" power supplies actually have some capacitance between the negative rail and ground. This, when coupled with the probe's connection to ground asymetrically loaded the two configurations resulting in a slower rise time when the probes were connected one way vs the other.
I meant to suggest that as a possible problem with your test circuit.

An easy way around the whole matter is to use a 9V battery as the power source for the transistor circuit. Then the whole circuit is fully floating with no significant capacitance anywhere, and you can connect the scope across anything, either way round, without affecting it. That's what I suggested to Adam in post #57.
 

davenn

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Hi Steve. I didn't say that, you know it's a photo transistor with a resistor connected to the collector. People might mock me on here but I can only state what I understand

excuse me but to quote what you said .....

Also did another experiment if your interested with a OP593 which shows an increase in current out of the emitter compared to the collector

Understand that in a series DC circuit, the current is ALWAYS the same everywhere

D
 
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Arouse1973

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I am getting confused now. The whole point I have been making whether right or wrong is with a photo transistors base terminal left open as I understand you can have more current coming out of the emitter than the collector. I am not always very good at explaining myself but from the numerous post I have put up hopefully people will understand what I mean. Sorry if I am not clear.
Thanks
Adam
 

eem2am

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I reckon the light coming from the base converts to current, and this explains Arouse1973.s extra current.

As we all know, even DC current has a field associated......and even DC current is really consistent of an EM field, and is not a flow of charge...but it doesn't hurt to think of it as such for low frequency circuits.

In our year three BEng Electromag course, the lecturer got up and started by saying "everything we have taught you so far is a lie"

he was right, it was, but if you can lie and get the design done, then who cares?
 

KrisBlueNZ

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How can there be more electrons flowing into the emitter than flowing out of the collector? Where do the extra electrons go? They can't travel to the LED, or out of the package, because the package is an insulator.

And can you explain the difference between your claim that "with a photo transistors base terminal left open [...] you can have more current coming out of the emitter than the collector" and Steve's re-statement that you're claiming to have "a series circuit where the current at one point differs from the current at another point"?

As far as I can see, the claims are the same.
 

(*steve*)

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Also, if more electrons are coming out of one lead then either electrons are being injected somewhere (are you illuminating it with an electron beam?) OR the device will rapidly gain an electrostatic charge.

Apart from anything else, that electrostatic charge will act counter to this electron flow and pinch it off, or even reverse it.

We see none of this behaviour with optocouplers.
 

Arouse1973

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I reckon the light coming from the base converts to current, and this explains Arouse1973.s extra current.

As we all know, even DC current has a field associated......and even DC current is really consistent of an EM field, and is not a flow of charge...but it doesn't hurt to think of it as such for low frequency circuits.

In our year three BEng Electromag course, the lecturer got up and started by saying "everything we have taught you so far is a lie"

he was right, it was, but if you can lie and get the design done, then who cares?

Yes its the same for chemistry and physics also. Most electronics books are also wrong in many ways. But it still all works the way it teaches but that does not make it right. I mean even seasoned engineers still think a battery contains the free electrons that are used in the circuit. Also the term current flow used by many people even on here is incorrect. Thats like saying flow of charge flow. I myself use it but try hard not to.
Adam
 

davenn

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WARNING

this thread is getting very close to being closed due to the large amount of garbage you are spouting eem2am

Dave
 

Arouse1973

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Dave
Let's please wait until I have heard from my contact in Australia. He will put this to bed.
Cheers Adam
 

(*steve*)

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Dave
Let's please wait until I have heard from my contact in Australia. He will put this to bed.
Cheers Adam

Hmph! Australia. Who trusts anyone from there? All I can say is that if he's from a backwater like that he better also come equipped with some pretty powerful evidence.

Next worse are the English. But at least they can play cricket!
 

davenn

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Dave
Let's please wait until I have heard from my contact in Australia. He will put this to bed.
Cheers Adam

unless the citing's come from peer reviewed papers it wont mean diddly squat
 

KrisBlueNZ

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unless the citing's come from peer reviewed papers it wont mean diddly squat
Unless he agrees with us, in which case we'll accept his opinion as absolute, conclusive proof, right? :)
 
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