Reg. Free Wheeling Diode

Please see, good explanation is given with sketch

http://en.wikipedia.org/wiki/File:Flyback_Diode.svg

Results 1 - 10 of about 43,700 for freewheeling diode. (0.21 seconds

Better still,

Results 1 - 10 of about 16,400 for "freewheeling diode". (0.17 seconds)

http://www.google.co.uk/search?source=ig&hl=en&rlz=1G1GGLQ_ENUK318&q=%22freewheeling+diode%22&meta=lr%3D

and the first result is

http://en.wikipedia.org/wiki/Flyback_diode

which is slightly more explicit than the first wikipedia reference.

Well done, that is what the OP could have also done and not got any Flak from me or anyone else AND he might have learned something (Like how to find references...)

You are not much of a learner if you need CR4 to hold your hand for such simple questions....

Go and get a PROPER education.....

Be fair Andy, the Q and A aren't that simple...
I'ts the looking it up that's soooooo easy.

(I had to check up the topic when building the speed controller for my golf trolley)
BTW I was guest at #2

Del

But did you bother to ask CR4? Of course not!!

I find answers to all my technical questions without bothering anyone on CR4 (lucky I guess).....I have never started a Blog here with a question, only answers......simply no need up to now.....but of course if I did have a question that could not be answered from the web, I would post it here like a shot!!

I have nothing against reasonably difficult questions being posted here, even if the answer lies on the web somewhere, but simple questions like this need to be researched first.......

The answer probably lies in with the fact that many people have not learnt enough to understand the answers they find or are given, they simply do not have the back ground knowledge.....they will probably not understand our answers either.....

Have a good one....

Andy,

I agree that often people annoyingly try to use this forum as a starting place to solve a problem or to educate themselves. I have no problem with this in principle, but the poster of the question should show some knowledge of the system and ideally why they cannot grasp why things are done this way.

For example, in this case if the questioner had asked:

"Why is there a reverse biased diode in a buck switching supply? A friend who tried to explain this to me called it a freewheeling diode. What does that mean?" We would know the questioner understands circuit symbol designation, the fundamental non-linear nature of a diode and some basic understanding of what the whole circuit is supposed to do. The more we know about the circuit and the difficulty the questioner is having, the more we can help. It also permits us to scale our answer to the level of understanding the poster has.

So don't be too hard, I know I have at times and regretted every time.

Your idea of how the question should have been was well thought out.....

There is a saying in Germany, which makes sense in German but not in English, which basically says "the manner in which you ask the question, dictates the tone of the reply!"

Write it in German too.

Wie Mann in den Wald hinein ruft, so schalt es heraus.

How one in the forest calls, so sounds it back out.......(sort of echo effect, but the word echo was not used.... Wald is forest and moor.....but here it means forest)

I have translated it as near as possible word for word, but it sounds crazy in English still......

I played with an online translator and got this more literal rendering.

Die Weise, in der Sie die Frage stellen, Vorschriften der Ton der Antwort.

Lovely, which translator did you use???? Give me the URL please...

We used to play a game at work, translate a saying as badly as possible into another language, and the others have to guess what the original saying and language was.

For example (it happens many times with many words) in German the part word "Schirm" is used in many words, for example:- Bildschirm is a Screen or TV, Fallschirm is a Parachute, Regenschirm is an Umbrella......so you can really play around with such a translation!!

I noticed that many questions are posed without much supportive info.

Also the persons could probably do well by GOOGLE if they know how to put in the key words. And many folks seem to struggle with vocabulary more than language. I know that engineering people struggle with their own native languages so it must be tougher for a foreign speaker here.

Translated from one language to the other and then turned it around with amazingly strange results.

http://www.dict.cc/ This one talks.

Wie man in den Wald hineinruft, so schallt es heraus.
proverb: What goes around, comes around.
proverb: As the question, so the answer.

The free online translators are pretty stupid but they help.

I don't remember what I used to get these.

The manner in which you ask the question, dictates the tone of the reply.
Die Weise, in der Sie die Frage stellen, Vorschriften der Ton der Antwort.

The way in which you put the question, rules the sound of the answer.
der Weg, auf den Sie die Frage stellten, herrscht(entscheidet) über den Ton der Antwort.

Jon

Some of the translations are quite good, one is totally wrong......

Thanks for the link, I will have a look later.

I figured that. See what I mean about those off the wall translators?

And Russian translations are next to impossible.

Jon

There is a good link on my golf trolley building blog...
Del

in short words , the free wheeling diode prevents having a spark (depending on the current of the circuit) when you switch off the circuit . of course that doesn't mean that it's optional .

...its called "Back EMF" and many transistors (and the like) will be damaged if the spark is not damped out with such a diode....

Its often/mostly inductive loads that cause the BEMF, even a small relay coil can do it......

Dear Sir,

Thanks for the reply.

The free wheeling diode in the charger application provides a path for the inductor current when the rectifier diode is no longer conducting and the magnetic field is collapsing. This provides a boost current to be applied to the output.

This works especially well in higher frequency applications such as aircraft 400 Hz systems.

It is used to provide a smoothing efffect to the output filters in more refined power supplies.

The would be "spark" refered to in other posts is captured and used to hold up / add to the output power during the input power "rest period".

Why waste a good inductive kick.

Jon

In the relay world we call it a suppression diode (does the same job for the relay coil as the output windings of a charger transformer). If you are going to use one in a design, may I suggest a series diode to protect the suppression diode? This would provide reverse polarity protection for the suppression diode in case someone hooked a battery up backwards by accident. The R.P.P. diode would need to be rated for the full load charging current. The suppression diode only has to be rated for the current necessary to discharge the Back EMF voltage spike of the transformer output windings, which can be 5-10 times the voltage across L + R.

Talk about [spark] supression circuits, can anyone explain the logic behind Bates' formulas? They were proposed in "Contact arc suppression of electromagnetic relays", by C. C. Bates in Electromechanical Design, Aug. 1966. Too early to be found on the web...

We used to learn that if you model a relay winding as a series RL circuit, transient suppression will occur if you connect a series RC ckt in parallel (provided the time constants are the same: RC = L / R; total ckt will behave as purely resistive). But then the relay's inductance will change as it opens...

I guess Bates' formulas are mixed theoretical / empirical. They yield much smaller C values and are widely used. Inductance values are probably derived from typical catalog ranges and correlated to current ratings.

C = I^2/10

Rc= Vo / [10*I^(1+50/Vo)]

where Vo = source voltage

I = load current at contact opening

Rc = resistance of RC network (ohms)

C = capacitance of RC network (microF)

Hi Snel,

I assume that the RC in parallel with RL snubs like a resistive tuned circuit.

The inductance of the relay coil is affected by the "effective core" by the change of the proximity of the relay armature. Would you ignore the change due to its significance or calculate it into the selection of the parallel RC components?

Due to high voltage would the RC parallel components be too obtrusive and the more desireable compact diode package desired?

Do you think the RC snubber and the diode clamp are selected based on the type of driving components and their ability to survive inductive kick?

Jon