Explain the process please

[Robocop]

I have been reading many posts on simple boost circuits and have learneed many new terms.Some of these are inductors,ferrite coils,resistors,...etc:
Can someone tell me where current goes or exactly to what parts once it enters the boost circuit.
Lets just use a simple AAA Dorcy board for example.Once battery contact is made with the spring contact on the bottom of the board what is the path of current through the board until it exits the other end powering the LED?
I see many small parts on this board and am curious as to each parts name and function and what order the current reaches it.
I know this is a technical question but I just thought that some of the electronic wizards here could surely identify these parts.
I am basically trying to learn the names of each part involved in a boost circuit in order to experiment with making one just for fun.I have had the actual process of how it works explained very well by several members here but am missing the steps the current takes from start to finish.Thanks for any help on this.Once I know the parts involved in a simple boost circuit I am going to start learning the ones involved in a regulated boost circuit...but that is a whole different thread.

 

[carbonsparky]

From what you say, I gather you are very new in the subject of electronic circuits. There is no simple, within the scope of this forum post to get you where you are asking to go, but I hope this might get you on the road.

I did a quick Google search and found this link.
http://science-ebooks.com/electronics/basic_electronics.htm

This will give you a place to start at and to understand the basic function of the circuit elements you mentioned. After you understand these basics you can ask more direct questions on this forum and be able to get more useful response.

If you wish to see some samples of boost circuit schematics, just do a search for "boost circuit" or "boost regulator" and you will find something. You should even be able to come up with a link that will even explain how the circuit works step by step.

 

[Doug Owen]

[ QUOTE ]
Robocop said:

Can someone tell me where current goes or exactly to what parts once it enters the boost circuit.



[/ QUOTE ]

Fair enough question, unfortunately not a simple answer.

The 'key to the castle' is the inductor. It's basically an electromagnet. Current in the wire winding causes magnetic fields to form. The 'trick' is the *change* in magnetic field (not it's absolute value) is linked to the current. In a typical boost converter a transistor is turned on and conducts more and more current through the inductor building up the magnetic field. When the transistor turns off, the collapsing magnetic field generates current ('trys to hold the current constant') in that same coil. A (hopefully low loss) diode switches so that this current is added in series with the existing battery, boosting the voltage total.

Gig is for a time the current doesn't exist. The energy is actually stored in a magnetic field......

It won't work electron for electron, it can't, there's more electrons the the Battery than the load.

Doug Owen

 

[Robocop]

Yes I agree a more specific question is in order but I really can not narrow one down.I was hoping for some names of each piece involved in the process.I did a search prior to this thread and learned much of the actual process involving these circuits however the actual parts that made it happen were not found.
Basically what I am curious about is the pathway the power takes such as when the current travels up the contact spring to when it exits the circuit.A good example would be to complete this statement.Voltage enters at 1.5 volts and goes directly to the ______ and then travels to a ______ where it circles around the ______ and finally exits the circuit through the ________ where it is now 4 volts.
I know it seems a little hard to explain but the searching did not really mention any specific component by name.
I am now trying to search the web and this site to see if I can actually identify each part on this Dorcy board by simply looking at pictures of parts.
I agree there is no simple circuit but most of the sites I found I do not understand simply because I do not know what part they are referring to.
So far I have identified the small resistor and coil on this board but have a few more parts to go.Once I identify each one then I want to learn what part each one has in the process as well as what point in line it receives current

 

[Robocop]

So the coil with the gold colored wire wrapped around it is called an Inductor?I think that that is a good start for me...hehe.I am thinking this due to your post above Mr.Owen where you stated the inductor is the key with current in the wire.By wire coil I assume that this little coil is the inductor...hope that is correct.

 

[MrAl]

Hello there,


What Doug is saying is that the inductor is the most important part of
the circuit and so understanding that will lead to an understanding
of an entire circuit with little extra effort.
With this goal in mind, we begin to look more closely at
the inductor to find out what this does for the circuit.

Im guessing you've already used rechargeable batteries, so
lets start there...

You already know when you charge a battery for some time
(charge time) you can get power out of it after the charge
time is complete. If you have a 6v battery pack you know
you'll get about 6v out of it after the charging is done.
You should also know that if you charge the battery for
about 2 ampere hours you can get approximately 2 ampere
hours out of the battery (minus losses). This means
maybe 1 amp current draw for about 2 hours.
Here, we put 2 ampere hours at 6v into the battery and
we got 2 ampere hours at 6v out of the battery. Note
that we could draw 1 amp at 2 hours or 2 amps for 1 hour,
or even 1/2 amp for 4 hours, while the voltage is
fixed at 6 volts.

Take note of these two things:
[1]
For a battery we charge with a (somewhat) fixed
current, but when we drain the battery we can draw
any level current we want from it but the voltage stays
constant.
[2]
When we CHARGE the battery we use one circuit (the charger),
when we DRAIN the battery we use another circuit (flashlight).

Now if you can understand these points you already understand
the inductor from an external circuit point of view (which is
good enough to start with) because the inductor acts like
a small battery.

Now for the details about the inductor:

[1]
We charge with a fixed voltage and allow the current to ramp up
to some value. When we drain the inductor, the voltage goes
to whatever value is required by the circuit (such as an LED)
and the current ramps down.
[2]
When we CHARGE the inductor we use one circuit (a battery + switch),
when we DRAIN the inductor we use another circuit (LED + switch).


The main difference between the inductor and battery is that
the battery has a constant voltage and allows the current drain
to be whatever the circuit requires, while the inductor trys to
hold the current constant and allows the voltage to go to whatever is
required by the circuit.

Since the inductors voltage can swing up to almost any level (10v, 20v, etc)
once it is disconnected from the power source (battery) this is what gives it the
ability to boost the voltage of a 1.5v cell to 4 volts or more.
Since in practice the inductors current ramps down we have to recharge the
inductor over and over again after every discharge cycle is complete.
We also have to do this very fast, typically 100,000 times per second,
whereas a battery charges over a period of 14 hours or so.


Lets recap a bit...

There are two modes of operation:
[1]
charge
[2]
discharge

There is a different circuit associated with each mode of operation:
[1]
Input circuit (charge)
[2]
Output circuit (discharge)

The inductor acts as a small battery:
A battery charges with a current, but the inductor charges with a voltage.
A battery discharges with whatever *current* we want use,
the inductor discharges with whatever *voltage* we want to use.
The relatively small inductors used with switching circuits must be
charged and discharged much much faster then when using rechargeable
batteries.

One last note:
If you could move your hand VERY fast, you could connect an
inductor across a battery, then disconnect it and connect it
across an LED and the LED would light up, for a very brief
period. Of course you couldnt move it fast enough with
your hand, so perhaps you could arrange two switches--
one to connect to the battery, and one to connect to
the LED after it's charged. You'd have to switch each
switch very very fast however :-) This is basically what a
boost circuit does using a transistor for one switch and
usually a diode for the other switch.


Take care,
Al

 

[Robocop]

MrAl you sure do know your stuff with electronics.Thanks for the brilliant explanation.I do have the basic grasp of this and understand that it is the high speed of the inductor being charged over and over to make this work.I did not realize it happens as fast as you say and that kind of speed(100,000 times a second)is almost hard to even imagine.
Is the inductor the first place the current goes after leaving the battery?Then it goes between the transistor and diode to create the switching on and off effect?
Thanks a lot for the info....This is incredibly interesting to me

 

[Harrkev]

Try this thread:
http://www.candlepowerforums.com/ubbthreads/showflat.php?Cat=&Board=UBB6&Number=425543

It explains the process quite nicely...

 

[MrAl]

Hi again Harrkey and robocop,

I was wondering where that thread went :-)
Thanks for bringing it back.

Here's a little more of an explaination of where
the current flows in a
boost circuit with no output capacitor...

[Using conventional current flow + to -]



------Circuit description------------------------------------------------
INPUT CIRCUIT:
Battery, inductor, transistor switch.

OUTPUT CIRCUIT:
Battery, inductor, diode, LED.
-------------------------------------------------------------------------


CHARGING INDUCTOR THROUGH INPUT CIRCUIT:
[mode1=transistor 'on', diode 'off']
The current flows from the battery+ through the inductor
then through the transistor switch (it's on) and back to
the battery- for a short time period. No current flows
through the LED. The inductor is charged up. The polarity
of the inductor is the same as the battery polarity
(plus to plus, minus to minus). The voltage of the
inductor is the same as the battery voltage (1.5v).

DISCHARGING INDUCTOR THROUGH OUTPUT CIRCUIT:
[mode2=transistor 'off', diode 'on']
The current flows from the battery+ through the inductor
then through the diode switch then through the LED then
back to the battery-. The inductor is being discharged.
The polarity of the inductors voltage is opposite to
when it was charging (ie it reversed when the transistor
switch opened up) so its voltage adds to the battery voltage
to make the total voltage higher. Its voltage is just enough
required to add to the battery voltage to overcome the diode
voltage drop and the LED voltage drop.
This means if the required LED
voltage is 3.5 volts and the required diode voltage
drop is 0.5 volts and the battery voltage is 1.5 volts
then the inductors voltage is 3.5 + 0.5 - 1.5 = 2.5 volts.


Note that the switching action of the transistor
makes the inductor look as if it was 'disconnected'
from the circuit so it's voltage reverses and changes
level in order to satisfy the output circuit voltage
requirements. Once the transistor is off, the inductors
voltage now adds to the original
battery voltage so we can get a higher voltage level
on the output which is required to drive an LED.
Once the diode conducts (switches on)
the voltage requirement is met and the LED conducts.


Take care,
Al

 

[Robocop]

MrAl once again you have done a perfect job in your explanation.That is exactly what I was looking for.I needed the name of each component and the order in where it received current.Thanks again for the help on this.

 

[MrAl]

Hello again,

Well glad i could help. I usually like to help people understand
things related to electricity and electronics so that they can
go on to do more related things and because i was once in the dark
about many things like this and know the feeling of how hard it is
to get information sometimes. I still dont have answers to
many of my questions in physics because they dont exist (yet).

To expand slightly on what we have been talking about, i have to
add (although a little reluctantly) that at the sub atomic level the
current is considered to be the same everywhere in the series circuit.
In other words, if we had say three resistors in series with a
battery and called them R1, R2, R3 and Batt, if the current was
say 1 amp then no matter where we measured the current we would
measure 1 amp. If between R1 and R2 we would measure 1 amp,
if between R2 and R3 we would measure 1 amp, etc., etc.
The explanation in some physics books is as follows:
Imagine a pipe wide enough to hold just about 1 billiard ball,
and long enough to hold quite a bunch of them. Now imagine
the pipe is bent in a circle, so that the inlet and outlet
come together and are joined. Now the pipe is filled with
balls that just touch each other and form a column that
circles around. To get a 'current' to flow move one ball
to say the right at the top, and since that touches the
next ball that next ball moves to the right also, which pushes
the third ball to the right and so on. The 'last' ball pushes
on the 'first' ball and the cycle continues around the loop.
The balls are somewhat analogous to the charges flowing in a
series electrical circuit.

Although the above is most true in real life, it still ends
up being more convenient to think of the current as flowing
through one device, then the next, then the next, etc.
In our little circuit with the three resistors it doesnt
really go through R1 then R2 then R3 in that order, it goes
through all three at once, but it's still a bit easier to
think of it as flowing through one at a time and then finally
back to the battery. It works out i guess because in a
circuit like that we have to take the time to think of
the voltage drop across each resistor in turn anyway,
because as humans we cant compute the voltage drop across
EVERY resistor in the circuit at the same time anyway.
Even a computer has to take some time to compute each
value in turn, so we shouldnt feel bad that we have to
also. Nature is a bit different, but that's not
our fault either :-) If we have a method that works
with every circuit we could ever encounter, we have
done well, even though we have not mimicked nature perfectly.


Take care,
Al

 

[Harrkev]

MrAI...

Look at it this way. If you have a device which had electrons flowing into it, and FEWER electrons flowing out, eventually the part would build up a negative charge. Once it reached a few hundred volts or so, ZAP!

If MORE electrons flow out, it will build up a positive charge...