how does a step up work?

[Robocop]

I am looking at my Dorcy AAA board and notice a small coil of wire attatched.It is gold color and wound tightly around a small spool.Is this the step up part of this board?If so how does this work basically?Volts go in one end and somehow increase when exiting the coil?I ask this as I like this board and use it as a doner in many mods however this coil is the most fragile part.It often breaks or gets in the way as it protrudes out more than the other components.I am just wondering if I could move it or somehow make it smaller.It is a mystery to me how this step up part works as it appears to be a simple coil of fine wire.Is it really this simple as running voltage through a coil of wire to increase the output?As you can tell I am a beginner and need some wisdom.Also if this is not the step up part of this circuit what is it?Will it hurt to put a blob of super glue on it to make it a little less prone to breakage when modding it to another body?Thanks for any help on this.

 

[paulr]

The coil is an inductor. When you run current through it, it generates a magnetic field. When you take away the load, the magnetic field collapses as the inductor tries to keep the current steady (similar to how a capacitor tries to keep voltage steady). The collapsing field causes a spike in the voltage across the inductor. The rest of the circuit captures that higher voltage in a capacitor and uses it to run the led. The coil in an automotive ignition system works pretty much the same way, except instead of boosting 1.5 volts to 3 or 4 volts to run a led, it boosts 12 volts to several hundred volts to fire the car's spark plugs.

 

[Doug Owen]

It's not just a coil, there's some serious electronics in there as well. Basically a power oscillator.

Trick with step ups is they run in cycles. First energy is stored in some element (usually stored magnetically in an inductor, although some use capacitors). Then, on a later part of the cycle this energy is recovered and is added to the existing battery, the total drives the LED. Then the cycle repeats, charge, discharge, charge, discharge. Tens of thousands to a million or so times a second.

Doug Owen

 

[Steelwolf]

[ QUOTE ]
It's not just a coil, there's some serious electronics in there as well. Basically a power oscillator.


[/ QUOTE ]

He means the electronics in the rest of the circuit. The coil is just basically a ferrite core and quite a number of turns of wire. /ubbthreads/images/graemlins/grin.gif

So to put it all together, the circuit controls the current from the battery to the coil, switching it on and off many thousands of times per second. As the current flows through the coil, a magnetic field is created. When the battery is switched off, the magnetic field collapses. A by-product of the collapsing field is that the energy needs to go somewhere and that becomes electrical power. Power being a product of voltage and current, the coil will be able to supply any reasonable combination of the two, hence the boost in voltage so that it is sufficient to meet the Vf of the LED. And since it happens so many thousand times per second, the pulses of the LED lighting up appear continuous.

Putting a blob of superglue or epoxy or hotglue to secure it and give it a protective encasement will not hurt it in any way. In fact, it should be done if your circuit is to be as physically robust as the LED it powers.

When CMG first introduced the Infinity, the circuit was not potted. I carried one in my pocket when I went ice-skating with some friends. Now, I'm a hopeless skater and spent as much time falling down as I did actually skating (note: that is time spent FALLING down, not time spent ON the ground /ubbthreads/images/graemlins/smile.gif ) The next day, I found that the light wouldn't come on. I opened up the circuit and found that the coil had broken loose.

 

[PhotonBoy]

Dorcy probably doesn't pot the coil or the circuit board for cost reasons. Due to the relatively low mass of the coil, it should stand up to most normal shocks, like dropping it, etc.

Ice skating rinks in western Australia!! Isn't it really hot in that part of the world?

 

[Harrkev]

If you REALLY want to understand how this stuff works, an analogy is in order...

You can replace a battery with a water pump, a resistor with a water restriction (a plate with a small hole in it). A capacitor becomes a large drum with a rubber diaphram in the middle, and an inductor becomes a passive turbine (a free-spinning heavy fan blade). Voltage then becomes water pressure, and current become gallons-per-minute.

A boost regulator works by connecting the turbine (inductor) directly to the pump (battery). As the water (current) starts to flow, the little propeller begins to spin real fast. Once it is going fast enough, you disconnect the pump and connect the load across the inductor. That little spinning propeller will force water through the load at more pressure than the pump alone could provide, but it slows down REAL fast. So you have to keep on switching the inductor between the battery and LED very fast.

This is GREATLY simplified, and omits a lot of details, but this is the general idea. There is also no such thing as a free lunch. The battery supplies a low voltage at high current, and the regulator outputs high voltage at low current.

 

[Robocop]

Harrkey thanks for the analogy as that is terms that I can understand.I see now that the coil is only one link in the chain needed for a step up.I was just curious as to this piece as it it always the most fragile part and usually breaks off if handled wrong.Steelwolf also thanks to you for the info on securing this coil.I will attempt to cover it with super glue and hope this remedies my problem.I have been succesful in placing this board in a few different hosts and it works well but is quite fragile.Thanks again to all with input as I am slowly beginning to understand the technical side of my fast growing addiction.

 

[CM]

Harrkev,

That sounds like the analogy they use in Mechanical Engineering to teach gearheads how RLC circuits work /ubbthreads/images/graemlins/grin.gif Anyway, I could not have come up with a better analogy.

 

[paulr]

See, I was always an electronics guy, so the analogy went the other way for me: "if you really want to understand this hydraulics stuff, think of the water pump as being like a battery, the turbine is like an inductor, ..." /ubbthreads/images/graemlins/grin.gif

 

[Mark_Larson]

:clap: Good job on explaining this one, guys.

 

[CM]

paulr,

I got the same analogy. The spring, the mass etc. etc. /ubbthreads/images/graemlins/grin.gif

CM

 

[MrAl]

Hello there,

Another simple analogy is this:

Lets say we have a 'large' 2.4 volt battery driving our circuit.
The inductor acts as a 'small' battery that is totally discharged.
Once the power is turned on, the 2.4v battery is connected in
parallel with the small discharged battery (inductor) which then
quickly charges it up to 2.4 volts. Two 2.4v batteries in
parallel still only gives us 2.4 volts output, so it's still
not enough to light the Led which requires 3.5 volts, so next
we disconnect the small battery (inductor) and now connect it
in SERIES with the large battery. Since 2.4 volts plus 2.4 volts
gives us 4.8 volts, we've stepped up the voltage to twice it's
original value simply by changing the connection of the
inductor in the circuit. We now have enough voltage to drive
an Led.

That's the simple analogy, but in reality the inductor has
a special property that the 'small battery' doesnt. That is,
it can take that 2.4 volts from the battery (while it was
connected in parallel) for the time it was connected and
store it as a magnetic field within its core. Now once
we disconnect the inductor a very interesting thing happens.
We find that the inductors voltage shoots up to WHATEVER
VOLTAGE IS REQUIRED BY THE CIRCUIT (!) in order to make sure
the same current flows as was flowing at the instant we
disconnected it !! As a matter of fact, if we designed the
inductor right we could get 1000 volts out of this circuit!
In other words, the inductor acts as a battery of any
voltage that the external circuit can put up with before
it draws lots of current and eats up some of the energy
stored in the inductor. The inductors voltage not only
shoots up, it reverses so it even makes it easier to
connect in series with the battery once it's charged.
Because of this special property, step up circuits almost
always contain an inductor.


Take care,
Al

 

[Robocop]

MrAl your wisdom is appreciated and as always very welcome.I have came a long way since my early days of lurking in the forum shadows however still know very little.If I read your reply correct it seems that it is very simple yet complicated process.Is it really as easy as switching from series to parallel at a very fast pace?There must be some very complicated workings in these circuits.If I learn the basics of these simple circuits I feel that I can improve greatly.Your analogy has helped me greatly and as always I thank you for your time.This is facinating stuff to me and I have learned quickly that lights have came a long way in a very short time.

 

[PhotonWrangler]

[ QUOTE ]
MrAl said:
Now once we disconnect the inductor a very interesting thing happens.
We find that the inductors voltage shoots up to WHATEVER
VOLTAGE IS REQUIRED BY THE CIRCUIT (!) in order to make sure
the same current flows as was flowing at the instant we
disconnected it !! As a matter of fact, if we designed the
inductor right we could get 1000 volts out of this circuit!


[/ QUOTE ]
Great analogy, Al.

I found this out the hard way many years ago as a youngster. I had an old magnetic headphone with bare ends, and I decided to touch the bare ends to a 9 volt battery to see how loud of a click it would make. Once I released the wires from the battery, the magnetic field collapsed, inducing that big voltage, and I received quite a jolt! I remember thinking "HUH? A shock from a 9-volt battery?!"
That's when I learned about inductors... /ubbthreads/images/graemlins/blush.gif

 

[tvodrd]

[ QUOTE ]
CM said:
Harrkev,

That sounds like the analogy they use in Mechanical Engineering to teach gearheads how RLC circuits work /ubbthreads/images/graemlins/grin.gif Anyway, I could not have come up with a better analogy.



[/ QUOTE ]

Chris, I'm one of those "gear heads" and proud of it. /ubbthreads/images/graemlins/grin.gif

Larry

 

[MrAl]

Hello there Robocop and PhotonWrangler,

If you look at the simplest form of a switcher it has a transistor
collector-emitter junction connected to one end of the inductor,
while the other end of the inductor is connected to the battery.
With the transistor switched 'on' the inductor is effectively in
parallel with the battery, and it gets its charge that way.
Once the transistor is turned off, the CE junction opens but
there is still one end of the inductor connected to the battery +
terminal, which means the voltage on the (now) open end of
the inductor is free to rise up as high as it needs too in order
to force conduction in the output circuit. This open end
voltage rises up high enough to force a diode in the output circuit
to conduct (in circuits with a diode) and charge the output
capacitor. In circuits without a diode, the voltage rises up
high enough to force the Led to finally conduct.

It's kinda simple because there are only two states to
worry about -- the transistor 'on', or the transistor 'off'.
Some of the details get a little tricky such as how the
inductors voltage reverses. Here the funny thing is that
the inductor gets its property to be able to reverse the
voltage across it because of the collapsing magnetic field.
When the inductor charges, its field goes higher and higher,
and the voltage has the same polarity as the battery (it is
in parallel with the battery). When the transistor opens,
the battery is not used to charge the inductor anymore
so the inductors field begins to fall. This change in
the field (from rising to falling) causes the entire
voltage across the inductor to switch from positive to
negative (pretty amazing if you ask me!). This means
that the positive side of the inductor changes to
the other terminal.

Let me see if i can draw a picture because this makes it
much easier to understand:

B is the battery and L is the inductor and + and -
show the polarity of the inductor and battery at the time
and 'gnd' is circuit ground...
<font class="small">Code:</font><hr /><pre>
CHARGING:
|------|
|+ |+
B L
|- |-
|------|
gnd
</pre><hr />
<font class="small">Code:</font><hr /><pre>
DISCHARGING:
- +
|---L---
|+
B
|-
|
gnd

</pre><hr />

Note that in both circuits above the same terminal of the
inductor is always connected to the battery (+) terminal.
The only thing changed is the 'bottom' of the inductor
in the top circuit has been disconnected from ground to
form the lower circuit. This simple change (usually done
with a transistor) causes the inductors voltage to
reverse and the voltage at the + end of the
inductor (lower circuit) to rise to a high value.

If in the lower circuit we had an Led connected between the
inductor and ground, it would conduct and therefore light
up.

Compare the lower circuit (above) with the equivalent
circuit (for a small time period) below:

<font class="small">Code:</font><hr /><pre>
- +
|---B---
|+
B
|-
|
gnd
</pre><hr />

Here we replaced the inductor with a battery that has
the same polarity as the inductor did. This shows how
we get the extra voltage to drive the Led, as the
inductor acts as a second battery in series with the
supply battery for a short time period.
Because this period only lasts for perhaps microseconds,
we have to recharge the inductor again on the next cycle
in order to be able to have it ready to drive the output
again. This makes it look like a tiny rechargable
battery that gets recharged every cycle. It doesnt
take long to discharge this tiny battery, so the cycle
has to repeat very fast (usually around 100,000 times
a second).
In effect, every 1/100,000 of a second, we charge a tiny
battery-like circuit element (using the main battery)
so that we can switch it in series with the main
battery to develop a higher voltage. The voltages
add when in series so we get a higher voltage
then we could using the main battery alone without
a switching circuit.

PhotonWrangler:
As you found out, that voltage can go VERY high and can be
considered life threatening with some inductors. Some
caution has to be used when dealing with these things,
usually when they are out of circuit.
Of course an auto ignition circuit works on this
very principle too and we wouldnt want to go touching
the terminals of the ignition coil when the car is running :-)

Robo,
I like to help people understand whenever i can. I think
people get a reward out of understanding and building their
own Led lights and circuits. That's a good point you made
about how far lights have come recently. Now that i think
about it, im starting to see things i had hoped for some
two years ago. I've seen more and more products turn up
with Leds in them in stores all over now, while two years ago
only a few stores and not many products.
Also, ten years ago you probably couldnt find many lights
with a switching power supply built in them i bet.
Just batteries and a stupid bulb :-)


Take care, and good luck with your LED circuits & flashlights,
Al

 

[PhotonWrangler]

[ QUOTE ]
MrAl said:
Hello there Robocop and PhotonWrangler,

As you found out, that voltage can go VERY high and can be
considered life threatening with some inductors. Some
caution has to be used when dealing with these things,
usually when they are out of circuit.
Of course an auto ignition circuit works on this
very principle too and we wouldnt want to go touching
the terminals of the ignition coil when the car is running :-)

Al


[/ QUOTE ]
I know that NOW! /ubbthreads/images/graemlins/grin.gif I learned that rude surprise back in my early teens when I was putting together my first crystal radio receiver. After I was done playing with the radio, I got bored and saw that 9v battery sitting around, so I thought "I wonder if that battery has enough life in it to make a pop in this headset?"

I've since had a lot of electronics training, and I now have a much healthier respect for anything that can produce high voltages, including TV horizontal output stages, E.L. inverter supplies, power mains, ringing phone lines, etc. But I still manage to get the occasional shock, as I often have my fingers buried in some kind of circuitry.

Back when I started learning electronics, most of the stuff was still based on vacuum tubes (fire bottles!) and that's when I developed a healthy respect for the B+ plate voltage. /ubbthreads/images/graemlins/ooo.gif

 

[GrayFox]

I found this: Voltage Boost Circuit . It seems to show a boost circuit constructed with capacitors. See page nine for the block diagrams of the current flow.

--Jerry

 

[MrAl]

Hello again,

GrayFox:
Sorry that link didnt work for me.
Boost circuits that use one or more caps usually do
the same thing as with the inductor. Basically the
cap is charged with the battery and then switched
in series with the battery. The sum of the battery
voltage and the charged capacitor voltage provides
a higher voltage then with the battery alone.

Take care,
Al

 

[BB]

The cool thing about the DC to DC converters (switching power supplies) is that are very power efficient.

For example, you can purchase a simple 3 terminal regulator that does a very good job of voltage (or current) regulation--but they very inefficient. Basically, they are the equivalent of you regulating water flow (or pressure) by turning the water valve a little more on or a little more off while watching the output. Most of the energy is wasted (depends on input and output, but easily 50% to 99%+ loss) as the water goes through the valve (restriction/resistor).

A DC to DC converter uses the inductor's energy storage ability to transform it to a higher or lower voltage. Now the losses are much lower (typically 10-20% loss). In these type of circuits, they mimic a transformer where the power in is equal to the power out (minus losses). In other words, the Voltage*Current (input) = Voltage*Current (output).

I have heard all of the analogies listed above as I went through school--but my personal one that always worked well for me was to imagine:

Resistor = water valve
Capacitor = tank of water with hose at base
Inductor = Momentum of water in hose/pipe (think water hammer)
Diode = Check valve

Here is a basic step down DC to DC converter:
<font class="small">Code:</font><hr /><pre>
+--switch--+---Inductor---+-------Load
| | | |
Battery - LOAD CAP GND
| Diode |
| + GND
GND GND
</pre><hr />
A. Switch Closed, Power (current) flows through Inductor, slowly increasing in current to Load CAP (small local battery to even out the ripple voltage) and to Load. Diode (check valve) is reversed biased (closed) so no current flows.

B. Voltage (or current if current regulated) at Load gets to high set point.

C. Switch is opened (turned off). Inductor wants to keep current flowing in the same direction (think momentum in water pipe), and it is now acting like a battery (or turbine/flywheel) and continues to supply energy (current) to load. Note that current must come from somewhere, and that is the Diode.(check valve). This will continue until the energy in the inductor is depleted to the point that it cannot force more energy to the load.

D. Voltage (or current) drops to low set point and switch is now closed. Current flows in inductor, Diode is reversed biased (off).

Now do this hundreds to thousands of times per second (and get fancy and vary the "on time" of the switch in the cycle) and you have a switching power supply.

I have to go now (family Christmas time--wife is requesting me to get going, NOW!). Hopes this helps.

Sincerely,
-Bill

PS: I am not a power suppy engineer, I only play one on TV (systems engineer)

PPS: Post Fixed (using CODE function)

PPPS: A spark coil on an older (pre-electronic's car) is in the 10,000-20,000+ volt range).