DC for LED bulbs

Hi, did you see this? This was the electric power of the very simpleelectronic projects channel.

Yes, almost every light is flickering, notall the time just a couple of hours per day.

Better this than a blackout, ones can say.

Still, this is annoying.

As I said almost every light but there isa LED light that doesn’t flicker much.

The difference is in the driver circuit ofcourse, but the main reason is, inside of the circuit, the bigger built-in capacitor.

The LEDs likes DC power and we have AC powerso there is an AC to DC converter in every LED lamp plus the driver circuit.

In my previous video, link below, I made thisAC to DC converter.

As you can see, this is big and relative expensivea LED light bulb is small and cheap and have everything inside of it.

Probably you noticed that some lights whenswitched off, fades slowly and others go out very quickly.

As I said the difference is in the capacitor, a capacitor is an energy storage device so if there is an extra capacity, the storedpower can help to fill smaller gaps in the main power supply.

Here are a couple dead lamps; you can seethere are small boards with very small parts on it.

There is utterly not much room for improvements.

Even the disassembling is often difficult.

I am sure there is high quality LED lightsolutions out there for a decent amount of money of course.

But my solution is cost-effective becauseI used an old PC supply here it is.

And here is one of my testing gadgets; thiswill help me in the demonstration.

Let’s start with this gadget, here I canswitch on the outlet, the neon light indicates the power.

This switch also reverses polarity, in thiscase, live and neutral; in some situations this is helpful.

This black switch is the main player in thisproject when I press it nothing happen just the neon light blinks.

Both sides are on but there is little timein milliseconds range when power is cut off.

So in the star wars manner of speaking thisdark switch bring disturbance in the force.

Let’s plug in a LED bulb and as you cansee the light is flickering.

The next step in this little demonstrationis the placing this box before the LED light.

Let’s do the test again and now there isno flicker and when I switch off, the light after few second fading out.

Inside is, of course, is an AC to DC converterso the LED bulb is now fed with DC.

At the beginning of the mass usage of theelectricity, there was a big disagreement between Edison and Tesla on what to choosefor main power grid AC or DC.

This is doesn't a point for Edison becauseDC power also can have disturbances.

The point is if the AC to DC converter isoutside of the light bulb then there are not many restrictions in the size; we can havea very robust solution.

Let’s check out what is inside this box.

Not much is there, as you can see I just stripthis board and leave on the needed parts.

This is schematic for a PC power supply butI just used this small part of it.

Here is in a bigger form, these supplies comein many variants but basically, most of them are very similar.

On input is an AC to DC converter with variousadditional filtering and protection circuitry.

This was lower class supply so here is theswitch is just on one side.

Speaking about switching and switches, thereare couple good reasons to switch on and off this setup here.

By here I mean on the AC side because if weswitch at the output, there is a high voltage DC.

DC power is way more difficult to switch, you can check out this by the data written on some switches.

This is the less problem because here is thepower low although we can plug in here ten or more bulbs and this should work in a similarway.

The bigger problem is the inrush current becauseevery time at the switching on we will have high current I will talk about this littlelater.

There is a fuse, another thing that we shouldhave but we, not professionals tend to forget.

And the PFC choke that is here actually beforethe fuse, also not very professional.

This thing is important not just because ofpower factor correction but because of inrush current.

Inrush current is a stressful event at poweringelectric devices basically very high current for a short period of time.

If you want a device that won’t die at ayoung age, you must limit the inrush current.

Often this is done by a special NTC resistorlike this but I noticed that if there is PFC choke then no such resistor is built in becausethe choke coil prevents the fast-rising of current.

Here is another choke a common mode choke, this is for suppressing electric noise usually in combination with capacitors, good to have.

There is the diode bridge.

Here is no selector switch but the rest issimilar, two capacitors in series because of higher voltage here.

Each capacitor has a bleeder resistor thewhole thing is a voltage divider and in order to have half of the voltage on capacitors, they have to have more or less the same capacity.

At the output, another special resistor avaristor or voltage-dependent resistor protect the circuitry from high voltage spikes, betterknown as MOV metal oxide varistor.

A fan is not needed here but a power outletdoes so here is on this adapter board.

And now let’s do more tests.

This one is very depending on input voltagedon’t have much self-regulation unlike the first one.

As you can see there is little flicker remain.

If we add a voltage regulation in this supply, from 200 volts and up, could be used as a dimmable bulb.

Maybe another time, more important I checkedmy setup with a power meter and there is a difference, around ten percent more poweris consumed, but that much shouldn’t cause a problem.

The last one, for now, this filament typeone.

And this is only good for a demonstrationof the inrush current.

And this flash, what we saw was the inrushcurrent.

Inside is a capacitor with a bleeder resistorin parallel, like this.

The flash was because the charging of theempty capacitor and this glowing is because the high-value resistor let through smallcurrent.

These bulbs are popular and more expensivebut I think they are worse.

Basically, this is a flickering all the timeat one hundred Hertz.

There are opinions that this is not good forhealth.

This is for now; if this doesn’t look veryprofessional to you this is because I am as far from an engineer as Austria from Australia.

Thanks for watching.


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