Inductive Kick and Snubber help

[giftiger_wunsch]

By convention, current flows from positive to negative. While it's true that when negative charge carriers are involved, such as electrons, they flow from negative to positive, that's not important.

By the conventions of physics/electronics, current is said to flow from positive to negative. Hence why the base of the 'arrows' of diodes is the anode, the positive terminal; and the point is the cathode, the negative terminal.

 

[Njguy]

By convention, current flows from positive to negative. While it's true that when negative charge carriers are involved, such as electrons, they flow from negative to positive, that's not important.

By the conventions of physics/electronics, current is said to flow from positive to negative. Hence why the base of the 'arrows' of diodes is the anode, the positive terminal; and the point is the cathode, the negative terminal.

Ok, so then they battery on the diagrams which represents a car battery, should be reversed?

 

[giftiger_wunsch]

Kinarfi's most recent diagram is identical to mine, just different arranged. It should work fine. He just confused the matter since he showed the current flowing from negative to positive, which is against the generally-accepted convention.

 

[Njguy]

Kinarfi's most recent diagram is identical to mine, just different arranged. It should work fine. He just confused the matter since he showed the current flowing from negative to positive, which is against the generally-accepted convention.

I don't know man, don't get me wrong, your a wealth of information, but I'm pretty sure when it comes to batteries it always flows from negative to positive. Read this, 3rd paragraph. HowStuffWorks "How Batteries Work"

 

[ericgibbs]

I was actually more confused when you said that. I figured power on a battery flows from negative terminal to positive. What were you saying

hi,
'Power' dosnt flow.

I would suggest if you are dealing with simple electronic circuits use the 'conventional' current flow,
ie: from the positive terminal, thru the circuit and back to the negative terminal.

If studying semiconductors, using the actual 'electron' current flow, negative to positive is sometimes more useful.

In your link how batteries work, he is explaining 'electron flow'

 

[Njguy]

hi,
'Power' dosnt flow.

I would suggest if you are dealing with simple electronic circuits use the 'conventional' current flow,
ie: from the positive terminal, thru the circuit and back to the negative terminal.

If studying semiconductors, using the actual 'electron' current flow, negative to positive is sometimes more useful.

Sorry, Electrons

I really don't see the point in going with convention when it seems rather counter intuitive.

 

[ericgibbs]

Sorry, Electrons

I really don't see the point in going with convention when it seems rather counter intuitive.

If you dont go with conventional flow, you are going to find studying heavy going and you will have to keep explaining to others that your circuit is based on electron flow.

Which IMHO is a waste of your time.

 

[giftiger_wunsch]

Keep in mind that electrons flow from negative to positive, but conventional current flows from positive to negative. It's simply the standard to prevent confusion.

Also bear in mind that we define current as flowing from positive to negative as it is not the same as the flow of charge carriers: while in wires etc. we're talking about electrons, passing a current through a sodium chloride solution will cause positive sodium ions to flow towards the anode and negative chloride ions to flow towards the cathode, i.e. in opposite directions to each other, but the direction of current flow is still positive to negative.

Current is the net effect of positive and negative charge carriers moving around; since electrons are negatively charged, electrons moving in one direction are carrying a negative charge, and therefore a negative current in that direction. If you think about it like that, it's actually very logical.

 

[Njguy]

How is this for a diode? SCHOTTKY RECTIFIER, 3A 40V | AllElectronics.com

 

[giftiger_wunsch]

Using a schottky rectifier is excessive and much more expensive than necessary. Just use a 1N4002 or similar as suggested earlier; they're worth a couple of cents each and will do the job just as well.

 

[Njguy]

Using a schottky rectifier is excessive and much more expensive than necessary. Just use a 1N4002 or similar as suggested earlier; they're worth a couple of cents each and will do the job just as well.

Ok, do I only need one per symbol?

 

[giftiger_wunsch]

The symbol is the symbol for a diode... it means 'a diode goes here'. Adding more diodes wouldn't contribute anything to the design. If you're planning on ordering diodes because you don't have any though, probably a good idea to buy some extras for any other projects you might need them for in future.

 

[kinarfi]

Convention flow of + to - was established before man could figure out how electricity worked, so they said, this is positive and this is negative and things move from more to less, that gives you conventional flow. Then we, man, got smarter and figured out that current, electrons, flow from more electrons on the - post to the fewer or lack of electrons on the + post of a battery, or any other power source. If you want to get complicated, let's discuss hole flow in transistors.

 

[giftiger_wunsch]

As I said before, it's much more logical to relate the net flow of negative charge to a negative current, and vice verca. Forget about actual direction; there is a positive current between a positive supply and a negative one, which makes it far easier to relate to the flow of charge, as the net flow of charge is therefore positive in the positive direction.

Therefore positive current relates to the net movement of positive charge, and negative current the opposite. It's not important whether this net effect is produced by positive or negative charge carriers.

 

[kinarfi]

I agree with you that we should use what we are used to using, I was taught the electron flow when I learned electronics in the 70s. I was wondering if the preference for one or the other might be related to locale or time, so, if you don't mind, where and when did you learn your electronics?

 

[crutschow]

Using electron flow is necessary when studying the operation of certain devices such as vacuum tubes where the boiling of electrons off the hot cathode and being attracted to the positive plate is basic to the tube operation.

Otherwise it generally is easier to just just use current flow. For example the arrows on the diode and bipolar transistor symbols indicate the direction of current flow, not electron flow.

 

[crutschow]

They're in parallel, not series. They don't cause a voltage drop.

I'm not entirely clear on how the parallel diodes work myself, nowhere I've read seems to explain it particularly, I just know that it's the accepted method for protecting components from the high-voltage spike due to inductive loads. I believe the diode short-circuits the inductor, allowing the magnetic field to drive a small current back through the inductor, which slows the rate at which the magnetic field collapses and prevents this spike reaching sensitive components elsewhere.

If someone could correct / expand on that it'd be helpful

It's really quite simple if you just follow the current flow. When a switch to an inductor is opened, interrupting the current flow, the inductance of the inductor will try to keep the current flowing. This generates a positive voltage in the direction the current is flowing (the bottom of the inductor if the current flow is top to bottom). If there is no place for the current to go, a very high voltage spike will be generated.

The diode across the inductor provides a place for the current to continue to flow. The inductor current flow generates a positive voltage at the anode of the diode which allows it to conduct the current. The current continues to flow until the inductive energy is dissipated in the diode forward voltage drop and the inductor's resistance. Note that the initial current flow in the diode is identical in value to the current flowing in the inductor just prior to the switch opening.

 

[giftiger_wunsch]

It's really quite simple if you just follow the current flow. When a switch to an inductor is opened, interrupting the current flow, the inductance of the inductor will try to keep the current flowing. This generates a positive voltage in the direction the current is flowing (the bottom of the inductor if the current flow is top to bottom). If there is no place for the current to go, a very high voltage spike will be generated.

The diode across the inductor provides a place for the current to continue to flow. The inductor current flow generates a positive voltage at the anode of the diode which allows it to conduct the current. The current continues to flow until the inductive energy is dissipated in the diode forward voltage drop and the inductor's resistance. Note that the initial current flow in the diode is identical in value to the current flowing in the inductor just prior to the switch opening.

Thanks for the clarification crutschow; hopefully that was as useful to the OP as it was to me.

 

[giftiger_wunsch]

I agree with you that we should use what we are used to using, I was taught the electron flow when I learned electronics in the 70s. I was wondering if the preference for one or the other might be related to locale or time, so, if you don't mind, where and when did you learn your electronics?

I learnt basic electronic theory in GCSE physics (2005/6), some additional information about capacitance, voltage, current flow, etc. while studying electrical activity in excitable cells as part of the first year of my biochemistry BSc (2008/9), and the rest I've taught myself by logical extension of what I already know, my knowledge of chemistry, and from posting on these forums

While it's possible that conventional current flow was originally devised due to lack of understanding of the physics, I think that it's now more appropriate as it provides a standard independent of the actual charge carriers which may vary, and makes it easier to relate mathematically. The net movement of positive charge in a direction is positive current; whether this movement was a result of negative charge moving against the current, positive charge moving with it, or both, is irrelevant to the net movement of charge, given as the current in amperes (coulombs / second).