Bulb takes AC supply and then...?

[purifier]

filament bulb in ac

Suppose there is a 100W bulb... I connect it to a bulb socket... What happens? DC Voltage is required for it to glow right? Or can AC make it glow? If DC is required, then how is the AC converted to DC? I am sure that the bulb cannot contain a transformer... How does it achieve this AC->DC conversion?

If i am on the wrong side of thinking, please correct me... And kindly tell me how these small devices are made to work on the 22V supply... Do they step down the voltage and how do they achieve that?

 

[usernam]

Bulb glows primarily due to the heating of the tungsten filament.
Heat dissipated is given by V²/R.
So even if voltage is AC, V² is always positive and heat dissipated is always positive.

 

[purifier]

Then what about other electronics devices... I'm not able to name them at this instant but suppose they require DC...then how does it get it without a transformer or a rectifier?

 

[salem_sajid]

Well as for as my knowledge is concerned if the appliance uses DC source to operate then it can be either operated on Battried or some rectification process has to be done to convert AC to DC.

Yet i have to see an Appliance designed for DC which is operating on AC or vice versa. Appliances are designed for a particular kind of Power Source and yes it is possible to have appliance which use Dual sources.

Hope that Helps

Regards
Ess ESS

 

[cedance]

Well as for as my knowledge is concerned if the appliance uses DC source to operate then it can be either operated on Battried or some rectification process has to be done to convert AC to DC.

Yet i have to see an Appliance designed for DC which is operating on AC or vice versa. Appliances are designed for a particular kind of Power Source and yes it is possible to have appliance which use Dual sources.

Hope that Helps

Regards
Ess ESS

i have seen these power backups using some sort of "SCR(silicon controlled rectifier)"... think that can also be used for giving an quivalent DC from that of AC. i remember a mcgrawhill book of 1000 electronic ckts contained that circuitry! hope this helps...

/Am

 

[purifier]

Wow... 1000 ckts... Do you remember the name of the book...? And so, these use SCR... Wonder how they use them...

 

[zootjeff]

At any point in time the bulb has some voltage across it. Because it is AC it has a varying DC voltage across it. At first there is nothing across it. Then after 25 percent of the cycle is complete it has a + peak voltage across it, say 140 volts, then at 50 percent of the cycle it has nothing across it, then at 75 percent of the cycle it has -140 volts across it.

The result is that it would pulsate at 120 hz, but this happens so fast that you don't see it.

AC just means that it has a DC voltage that changes very fast.

 

[salem_sajid]

Well SCR is also a rectifier . The member is asking if the appliances can be operated from AC without converting to DC (NO rectifiers ). WHich in my view is not possible as if something is designed to operate on DC then it cant be operated (at least not fully opertaional) on AC.

The concept of equivalnevce between the AC & DC i.e Effective Heating produced by them is used to equate AC & DC

Hope that helps

Regards
Ess ESS

 

[usernam]

Here's a link on SCR's if you are interested.
https://www.allaboutcircuits.com/vol_3/chpt_7/5.html

 

[smartsarath2003]

A bulb / similar devices glows continuously with DC supply. But with AC,they acrually flicker i.e On & Off, at 50Hz which can't be perceived by human eye. AC is just a time varying DC power. If you use a capacitor in line with AC, that can convert AC to DC,but is not a perfect DC

So most of the devices that operate with AC will operate with DC as well (except cepacitive loads). But not all the devices, with DC can operate with AC. Because they maynot responds well to 50Hz frequency and may blow even because of continuous ON/Off. Also in DC operated devices capacitors were used between +ve and -ve to,which becomes short when AC is applied

If you decrese the input voltage, the bulbs will come on dimly, that what happens during low voltage mains. But you can get a bulb/device of rated voltage equal to your supply voltage.

 

[Borber]

A bulb / similar devices glows continuously with DC supply. But with AC,they acrually flicker i.e On & Off, at 50Hz which can't be perceived by human eye. AC is just a time varying DC power. If you use a capacitor in line with AC, that can convert AC to DC,but is not a perfect DC

What do you mean by last sentence? How capacitor can convert AC to DC? Explain.

 

[smartsarath2003]

I am sorry I meant by smoothing capacitors.
It can convert a pulsing DC to perfect DC. So I thought the same for AC,but I think we need a diode as well

 

[ambidextrous]

Well according to me,bulbs (tungsten filament bulbs) can glow by ac or dc both type of supplies. All we need is to heat the tungsten filament to glow.
The bulbs in our houses or labs glow by an ac supply. that is they are not in "contious on" state infact they are going "on & off " with such a high speed (50 hz the ac frequency of our supply)that they seems continuously on.

 

[Borber]

Wolfram bulbs don't go on and off. Current through them actually goes through zero but they are during this period of time still heated and emitting light. Truth is, emitted light is amplitude modulated with frequency 100 or 120 Hz. Different is with neon fluorescent bulb.

 

[echo47]

Incadescent and fluorescent lamps both flicker slightly at two times the AC mains frequency, but they don't go completely dark between cycles. Fluorescent flicker is somewhat greater because its phosphor has a shorter time constant than the incadescent's filament. Here is a nice plot of typical flicker waveforms:
**broken link removed**

 

[maharshi_qis]

It will glow due to heating of filment..