does this circuit use conventional current?

Hi,

This is a Schmitt Trigger NAND gate (4093). The top and bottom terminals are Vdd and Vss respectively. Left is the input and the output is connected to the +ve terminal of LED. I don't see that the current is flowing into the output as LED is a diode. Btw, I think the current is flowing from top to bottom through the LED.

What do you mean by "conventional current"?

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I thought the LED was forward biased when current flows from ground, to the cathode, and then into the output (in the case of electron flow). This is why I thought the circuit was represented using conventional flow, where electrons flow from positive to negative.

I think I botched this term a bit -- sorry. I think it's proper to say conventional flow.

Thanks for your help.

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Mike

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If you don\'t know what\'s meant by "conventional current", then
what\'s all this:

"KodKodKod Learning Consulting - Here you get the answers" bullshit
about?

Hi,

Sorry, I didn't read carefully! You used the right term as John Fields said.

For a diode, the bar is the cathode and the edge of the triangle is the anode. And current flows from anode to cathode.

LED is just a diode. It can have both hole or electron flows (depends on how it is made). LED is forward biased when the anode has higher potential then the cathode and current (conventional) flows from anode to cathode. For electron, it flows in the opposite direction (from -ve to +ve as it is attracted by the E-field) and for hoe, it flows from

+ve to -ve as repelled by the E-field. However, since electron has -ve charge and hole has +ve charge, they contribue to the conventional current in the same direction.

So when you deal with diode, to determine whether it is forward biased or reverse biased, it is better to inspect the terminal voltage instead of how it is connected. In this case, we are sure the anode always has higher voltage than the cathode (which is connected to the ground). So the LED is forward biased. (Of course, the anode voltage is changing during operation and it can be too low (but still > or = ground) to turn on the LED and it doesn't lid).

Regards,

KodKodKod Learning Consulting

Thanks for the explanation of hole/electron flow. So, the answer to my question is: "Yes, this circuit uses conventional flow"?

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Mike

Hi, Mike. I'm not sure whether you're confident you've gotten a satisfactory answer yet. Here's a picture that might help (view in fixed font or M$ Notepad):

| | ~ | ___ ~ LED1 | .---|___|-->|-----. | | R1 ~ | | | ___ ~ LED2 | A |. | K | o---|___|--|

I see. That makes sense.

That also makes sense. I wasn't aware of those two different terms, so I'll be sure to look more into that subject. I wasn't aware that current could flow in to the output of a gate.

The ground symbol? Isn't this circuit connecting negative to ground? It seems like those two sentences are contradictory :)

My background is in software development, but electronics always has been a part-time hobby that I just never got into deeply. I understand a lot of the basic principles, including ohm's law, Kirchoff's law, capacitance, inductance, etc, but one of the things books (at least the ones I have) don't emphasize well enough is giving examples of breaking down schematics. Do you have any recommendations for a book devoted to this subject? I'll check out that CMOS cookbook you mentioned also. Thanks for taking the time to explain.

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Mike

Hi, Mike. There's always a certain amount of confusion about the word "ground" with newbies. Many times, "ground" refers to earth ground, like the green wire on a line cord / "cold water pipe" potential, &c. This is exactly what you should *not* do here. The only reason why your circuit will work is that it has a floating 3V battery power supply. If you connect the "ground" in your circuit to earth ground, you'll short out the phone TIP/RING as well as probably smoking the bridge rectifier. Not where you want to go. Just connect the negative side of the battery to everything in the circuit that shows that "ground" / circuit common symbol.

The key to reading schematics is finding out the function of all the elements of the schematic. You can then examine the way they interact. But knowledge of what the elements do is alwways the first step.

Again, if you want to know about CMOS logic gates (as good a place to start as any if you know some basics), "CMOS Cookbook" by Lancaster is just about perfect for a non-technical introduction. As I said, I believe it covers most all of what you're getting in your circuit. How to handle funky non-digital inputs, use of schmitt triggers as oscillators, using gates as buffer/drivers. It could also give you hints on how to improve your circuit (I'd start by having the output LED driven by a small logic level MOSFET). And it's a good, lively read. Among his other talents, Mr. Lancaster was a great columnist for electronics hobbyist magazines before they all died.

Good luck Chris

Thanks again for your help!

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Mike

No - the answer to the question in the subject line is "any circuit uses either conventional or electron current, depending on which you wish to use."

In the Beginning, early scientists studying electricity didn't know about electrons or other sub-atomic particles, so they somewhat arbitrarily declared that current was a flow of positive charge from the positive terminal of the power source, through the external circuit, and back to the negative terminal of the power source - this is what we now call "conventional current". Scientists and engineers have always analysed circuits using conventional current.

In the days of vacuum tubes, electron current was used when teaching technicians how circuits worked, as you can't readily explain vacuum tube operation using conventional current.

Circuits are not "designed to use conventional current" or "designed to use electron current" - the same circuit should result whichever way you think - as long as you don't change concepts in mid-stream.

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Thanks for explaining.

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Mike