Electronic Transformer & Electronic Ballast
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LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The former drives fluorescent lights and the latter drives low-voltage lights.
Okay for electronic transformer I have no problem but What I am asking is what is the output of an electronic ballast? İf the mains is 220 volt at 50 hz so the output of this guy is also 220 volt and 50 hz ? They talk about high frequency,I ask the relation of switching frequency and the output frequency.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Anywhere between 500v and 800v OC from what I remember seeing.
Not sure, but I imagine it's above 20KHz for inaudibility and parts size.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
1210201-225 EST
electrics:
Some broad concepts:
1. If you convert an AC source into a DC source, then with electronics you can from the DC source generate about any waveform and frequency you desire with electronic components, including different voltages, and AC or DC.
2. One way to make DC from AC is to use a rectifier and filter capacitor.
3. The higher the frequency of an AC supply the smaller you can make a transformer for a given power level.
So converting 60 Hz AC to DC and then converting this DC back to 20 kHz AC requires a smaller transformer than if a straight 60 Hz transformer was used. Less copper and less iron.
4. Many useful electrical devices can work just as well at high frequencies as at 60 Hz. Incandescent bulbs, fluorescent bulbs, other gas discharge devices, and power for electronic equipment. Not so for AC motors directly.
5. Fluorescent bulbs require a substantial voltage to initiate conduction, but also the source must, to some extent, have constant current characteristic. Gaseous discharge devices, fluorescents included, are some what of a constant voltage device in the region of interest for lighting, and to limit power dissipation the current must be limited. A constant voltage source can not drive a constant voltage load without some sort of problem.
6. The electronics can generate high voltage AC from low voltage DC and also control current.
7. Or the electronics can generate an output voltage of moderately constant magnitude with some upper current limit.
8. After the high frequency AC is generated it can be converted back to DC as is done in computer switching power supplies, or cellphone chargers.
.
electrics:
Some broad concepts:
1. If you convert an AC source into a DC source, then with electronics you can from the DC source generate about any waveform and frequency you desire with electronic components, including different voltages, and AC or DC.
2. One way to make DC from AC is to use a rectifier and filter capacitor.
3. The higher the frequency of an AC supply the smaller you can make a transformer for a given power level.
So converting 60 Hz AC to DC and then converting this DC back to 20 kHz AC requires a smaller transformer than if a straight 60 Hz transformer was used. Less copper and less iron.
4. Many useful electrical devices can work just as well at high frequencies as at 60 Hz. Incandescent bulbs, fluorescent bulbs, other gas discharge devices, and power for electronic equipment. Not so for AC motors directly.
5. Fluorescent bulbs require a substantial voltage to initiate conduction, but also the source must, to some extent, have constant current characteristic. Gaseous discharge devices, fluorescents included, are some what of a constant voltage device in the region of interest for lighting, and to limit power dissipation the current must be limited. A constant voltage source can not drive a constant voltage load without some sort of problem.
6. The electronics can generate high voltage AC from low voltage DC and also control current.
7. Or the electronics can generate an output voltage of moderately constant magnitude with some upper current limit.
8. After the high frequency AC is generated it can be converted back to DC as is done in computer switching power supplies, or cellphone chargers.
.
you explained so nice, thank you, I want to learn in fact the frequency concept used for electronic ballasti I mean if it produces a 50 -60 Hz mains with switching frequency of order of 15-20 khz . Or does it use 15-20 khz alternative voltage. I kindly ask you to send me an oscilloscope photo or scheme of one of these guys.
gar
Senior Member
- Location
- Ann Arbor, Michigan
- Occupation
- EE
110202-1128 EST
electrics:
I do not have time to create any scope photos for you at the present time. Someone else may be able to create some for you.
But I will try to verbally explain a little further.
1. From the 50-60 Hz mains you connect to a bridge rectifier, 4 diodes configured in a bridge type arrangement.
A bridge rectifier has two anodes connected together and two cathodes connected together. The paired cathodes are the positive polarity output, and the paired anodes are the negative polarity output. The remaining cathodes and anodes are connected so that a cathode connects to an anode. Then these cathode-anode pairs are connected to the AC mains.
See http://en.wikipedia.org/wiki/Diode_bridge
2. Across the bridge rectifier DC output is a large capacitor to reduce the ripple content of the rectified DC.
Now you have a DC source somewhat the equivalent of a battery.
3. If I chop a DC source on and off I have generated an AC source. But it has a DC component.
I could do this with a mechanical switch. This mechanical switch could be a round shaft with a copper conductor on one side and an insulator on the other side. This shaft mounted on a motor and two brushes contacting said shaft will produce a fast switch. It could be 60 Hz.
If I build a more complex switch, then I can remove the DC component. This would be desirable.
With an AC signal I can use a transformer to isolate and produce any desired output voltage.
3. If instead of a mechanical switch I use electronic components to create the switch, then I can switch at much higher frequencies.
See if this helps to this point.
In what country are you located?
.
electrics:
I do not have time to create any scope photos for you at the present time. Someone else may be able to create some for you.
But I will try to verbally explain a little further.
1. From the 50-60 Hz mains you connect to a bridge rectifier, 4 diodes configured in a bridge type arrangement.
A bridge rectifier has two anodes connected together and two cathodes connected together. The paired cathodes are the positive polarity output, and the paired anodes are the negative polarity output. The remaining cathodes and anodes are connected so that a cathode connects to an anode. Then these cathode-anode pairs are connected to the AC mains.
See http://en.wikipedia.org/wiki/Diode_bridge
2. Across the bridge rectifier DC output is a large capacitor to reduce the ripple content of the rectified DC.
Now you have a DC source somewhat the equivalent of a battery.
3. If I chop a DC source on and off I have generated an AC source. But it has a DC component.
I could do this with a mechanical switch. This mechanical switch could be a round shaft with a copper conductor on one side and an insulator on the other side. This shaft mounted on a motor and two brushes contacting said shaft will produce a fast switch. It could be 60 Hz.
If I build a more complex switch, then I can remove the DC component. This would be desirable.
With an AC signal I can use a transformer to isolate and produce any desired output voltage.
3. If instead of a mechanical switch I use electronic components to create the switch, then I can switch at much higher frequencies.
See if this helps to this point.
In what country are you located?
.
broadgage
Senior Member
- Location
- London, England
An electronic transformer produces low voltage at a very high frequency.
Commonly used to power 12 volt halogen lamps from a line voltage supply.
This is done by rectifying and smoothing the AC grid supply, then useing an electronic circuit to produce high frequency AC which is stepped down to 12 volts to work the lamp.
Within limits, the output voltage is constant despite variations in lamp wattage.
The wires between an electronic transformer and the 12 volt lamp must be very short due not only to resistance losses but also capacitive losses and inductive losses.
An electronic ballast is used to power flourescent or other discharge lamps from a line voltage supply.
The input is rectified and smoothed, then chopped electronicly into a high frequency, then transformed into the correct voltage and current to work the lamp.
The output voltage will vary according to the type and number of lamps driven, from as little as 30 volts, up to several hundred volts.
An electronic ballast is designed to give a roughly constant current despite variations in lamp voltage.
In the case of some types of flourescent lamp, a low pre-heating voltage is also applied to the heaters.
Commonly used to power 12 volt halogen lamps from a line voltage supply.
This is done by rectifying and smoothing the AC grid supply, then useing an electronic circuit to produce high frequency AC which is stepped down to 12 volts to work the lamp.
Within limits, the output voltage is constant despite variations in lamp wattage.
The wires between an electronic transformer and the 12 volt lamp must be very short due not only to resistance losses but also capacitive losses and inductive losses.
An electronic ballast is used to power flourescent or other discharge lamps from a line voltage supply.
The input is rectified and smoothed, then chopped electronicly into a high frequency, then transformed into the correct voltage and current to work the lamp.
The output voltage will vary according to the type and number of lamps driven, from as little as 30 volts, up to several hundred volts.
An electronic ballast is designed to give a roughly constant current despite variations in lamp voltage.
In the case of some types of flourescent lamp, a low pre-heating voltage is also applied to the heaters.
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