All these PCBs here are from Compact Fluorescent Lamps or better known as CFLs. In this video
we will understand the working principle of this light bulbs, the parts it has, the physics inside
of the tube and how the electronic ballast works. In this way we could understand why these light
bulbs are so popular now days, why are they a lot more efficient and very easy to control.
We will also see some disadvantages. I’ll show you step by step each component on the PCB,
tell you what each will do, and using animations, I’ll try my best to make you understand the
working principle of the circuit. Make sure you subscribe and hit the notification bell.
If you consider supporting my work, check y PATREON page. So, let’s get started.
What’s up my friends, welcome back. Here I have CFL light bulb. CFLs are just a compact
version of the common fluorescent neon tube with a compact electronic ballast in the base of the lamp
that is smaller and easier to install. This bulb is made out if two parts. The fluorescent
tube which could be curved, spiral or straight, and the electronic ballast.
The first fluorescent lights weren’t using an electronic ballast, but a combination of a choke
coil and a so-called starter. We will see these components and how they work later in the video.
If we look at the base of the tube, we can see that it has 4 wires coming out.
Inside, these are connected to some electrodes, one on each end. These electrodes are usually
treated with Barium. Interesting fact, that’s why you will always see the electrodes wires
winded around a metal connector instead of being soldered to the PCB. Since the electrode wire is
treated with Barium and the output wire is made out of other materials, it can’t be soldered
using normal solder so is easier to just wind it around a metal pin. The tungsten filaments
are inside of the tube which has vacuum so it is protected. Let's see what happens if you power on
the filaments without the vacuum protection. As you can see, they burn out in a second.
The CFL Bulbs consist of a switched-mode converter,
or Electronic Ballast, that functions on a very high frequency
and acts as a replacement of the Electrical Choke, and Starter assembly that we had a few years back.
First a little bit of physics. The tubes are filled with Mercury and Argon.
When current flows, the electrons will strike the Mercury and Argon atoms inside the tube, and
the energy is transfer to the Mercury atom, and that will push its electrons to a higher orbit.
When these electrons fall back to their orbit, they must release that extra energy
they have just received. They release the energy in form of Ultra Violate radiation.
Now this type of radiation is not useful for us, and is also dangerous, because it could give
us skin cancer. That’s why the tube is coated with Phosphor which is a fluorescent material.
This material receives the UV radiation and it will convert it into white visible light.
That’s how the fluorescent tube works. But there are a lot of unanswered questions. how can we
create the electron flow from one side to the other, why we have two electrodes, why we need an
electronic ballast, how to connect it and how does it work. First let me explain you the old circuit
with the choke ballast and the starter component and then I will explain you the new electronic
ballast step by step. Remember, we have our tube filled with Mercury, and an electrode on each end.
We connect our high frequency electricity on one input of each electrode. And the other two inputs
are connected together with a so-called starter. The starter inside has two thin metal contacts
that are normally open so they don’t touch each other. It also has a capacitor inside like this.
On one input, we place the electrical choke which usually is just a coil winded on a ferrite core.
When we first supply the circuit at let’s say 220V, the circuit is still open,
because the connectors inside the starter are not touching each other. So, as you can see,
electrons can’t flow from here to here in order to make the Mercury radiate UV.
But inside the starter we also have vacuum and the metal contacts are close enough
for the 220V to create an electrical plasma arc. This plasma arc will heat the connectors just
enough to change their shape and connect them one to each other. That will close the circuit
and now, a lot of current flows from one side to the other. That's how the tube will turn on.
Actually, here I have a close up and slow motion of the starter metal connectors, creating the
plasma arc. Is pretty cool to see, right? The arc is vibrating because we supply this with AC at 50
Hz. After some sparks, the metals connect to each other and close the circuit for a moment.
At this point, two things will happen. This current flow will heat up the tungsten filaments
and that will, start releasing electrons. But these electrons are still not creating
a current path from one side to the other, they have no force pushing them. But this current flow,
will also energize the choke coil, by creating a powerful magnetic field around it.
But you see, in just a few moments, the metal connectors inside of the starter are getting cold
and they will once again separate. So, the powerful magnetic field inside the
ballast will now collapse and as you know that will create a huge voltage spike.
Now, the voltage differential between the ends, is high enough for the current to arc inside the tube
between the electrodes. So now all those electrons are pushed from one side to the other.
Once the current path is made, the 220V is enough to keep this current flow going on and on.
We only need high voltage spikes at the beginning. Also, once current is flowing,
the ballast acts as an impedance in series, so it will lower the volage on the starter,
so it won’t flicker any more. So, that’s why we need the starter and the ballast coil and that’s
why at the beginning, the old fluorescent tubes were blinking a few times till the current path
was created. So, now electrons could flow, hit the Mercury vapor, create UV radiation which will then
hit the Phosphor coat on the tube and radiate visible light. Here I have a quick Example.
The phase of the 220V AC is connected to the ballast in series and then to left side of the
tube. The neutral is connected to the right other side of the tube and that same side is
connected to the starter which is connected in series with the left side. I power the circuit,
the starter flashes a few times and then the tube glows and it will stay that way.
Ok, not let’s study the compact electronic ballast.
The PCB of a CFL ballast circuit is a combination of four different circuits.
The EMI Filter Circuit, the Full-Wave Rectifier, the DC Filter Circuit and the Inverter circuit.
So, instead of the ballast and the starter, how else we could get that high voltage?
Well, using an electrical circuit made with transistors. As you can see on this PCB,
we have the main input connected to 4 diodes which is the full bridge rectifier.
Then we have this big capacitor acting as a filter and creating steady high voltage DC.
From here we have the inverter made with two transistors.
The output of the transistors is connected to a coil and another capacitor which is called
a resonant tank. You see, this PCB has not driver IC, so who will enable and disable the transistors
gate? The coil and capacitor create an LC tank which will resonate and by that we create both
positive and negative polarity waves. This coupled inductor here, each time the oscillation polarity
changes, since it is connected to a resistor and then to the gate of the transistor, it will turn
on and Off one and the other transistor. Our transistors will work with DC voltage.
So, first from those 220V AC, we place a full bridge rectifier.
But first, we usually have a fuse for protection and sometimes a resistor to limit the current.
The rectifier will rectify the signal as we have seen in the SMPS video and we get only positive
waves. We then add a capacitor which will filter the volage and give us a steady high voltage DC.
Now we add two transistors bridge. At the output of the bridge, we have our coils.
In order to create the high voltage AC, we first enable the bottom transistor.
So, the current will flow though the electrodes circuit from positive,
though the electrodes and then though the transistors back to ground. That will also store
energy in the coil as a magnetic field. But the coil has a capacitor on the side, so this would
create an LC tank. The magnetic field from the coil will collapse and charge the capacitor but
with inverted polarity and also higher voltage, since the coil will create high volage spikes.
Since the coils are coupled together, this process would change the polarity at
the gate of the transistors. So now the top transistor is ON and the bottom one is OFF.
That will create a current flow in the reversed direction. The magnetic field will now collapse,
charge the capacitor and invert the polarity at the transistors gate once again
and the process repeats on and on. That will create a high voltage high frequency signal.
This signal is used to power the fluorescent bulb and keep the current of electrons flowing.
That’s basically how the electronic ballast creates high voltage of around 1000V and also
high frequency. The frequency created in the CFL ballast is usually from 20 KHz to 80 KHz
because is proven that at higher frequency the light emission is better.
Once the CFL bulb glows, the voltage across will decreases to 230V and the ballast circuit
allows the current to flow through the tube. The good thing is that the filaments are in series,
so if they get damaged, the oscillation inside the circuit will automatically stop
so everything will be protected. So, guys, that’s how fluorescent light tubes work, that’s how they
glow using electrons and chemicals inside the tube and that’s how the compact version works.
If compared with incandescent light where a lot of power is lost in form of heat, one of the
biggest advantages of a CFL Bulb is the low energy consumption, which also produces less heat, has a
much higher lifetime compared to incandescent or halogen lamps, and produces pleasant light.
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